Virtualization - Jul 2021 - [PATCH v2 3/9] drivers/base/memory: introduce "memory groups" to logically group memory blocks

Hi,

this series is based on v5.14-rc2, with [2] on top. It applies cleanly
on top of linux-next of yesterday.


I. Goal

The goal of this series is improving in-kernel auto-online support. It
tackles the fundamental problems that:

 1) We can create zone imbalances when onlining all memory blindly to
    ZONE_MOVABLE, in the worst case crashing the system. We have to know
    upfront how much memory we are going to hotplug such that we can
    safely enable auto-onlining of all hotplugged memory to ZONE_MOVABLE
    via "online_movable". This is far from practical and only
applicable in
    limited setups -- like inside VMs under the RHV/oVirt hypervisor which
    will never hotplug more than 3 times the boot memory (and the
    limitation is only in place due to the Linux limitation).

 2) We see more setups that implement dynamic VM resizing, hot(un)plugging
    memory to resize VM memory. In these setups, we might hotplug a lot of
    memory, but it might happen in various small steps in both directions
    (e.g., 2 GiB -> 8 GiB -> 4 GiB -> 16 GiB ...). virtio-mem is the
    primary driver of this upstream right now, performing such dynamic
    resizing NUMA-aware via multiple virtio-mem devices.

    Onlining all hotplugged memory to ZONE_NORMAL means we basically have
    no hotunplug guarantees. Onlining all to ZONE_MOVABLE means we can
    easily run into zone imbalances when growing a VM. We want a mixture,
    and we want as much memory as reasonable/configured in ZONE_MOVABLE.
    Details regarding zone imbalances can be found at [1].

 3) Memory devices consist of 1..X memory block devices, however, the
    kernel doesn't really track the relationship. Consequently, also user
    space has no idea. We want to make per-device decisions.

    As one example, for memory hotunplug it doesn't make sense to use a
    mixture of zones within a single DIMM: we want all MOVABLE if
    possible, otherwise all !MOVABLE, because any !MOVABLE part will easily
    block the whole DIMM from getting hotunplugged.

    As another example, virtio-mem operates on individual units that span
    1..X memory blocks. Similar to a DIMM, we want a unit to either be all
    MOVABLE or !MOVABLE. A "unit" can be thought of like a DIMM,
however,
    all units of a virtio-mem device logically belong together and are
    managed (added/removed) by a single driver. We want as much memory of
    a virtio-mem device to be MOVABLE as possible.

 4) We want memory onlining to be done right from the kernel while adding
    memory, not triggered by user space via udev rules; for example, this
    is reqired for fast memory hotplug for drivers that add individual
    memory blocks, like virito-mem. We want a way to configure a policy in
    the kernel and avoid implementing advanced policies in user space.

The auto-onlining support we have in the kernel is not sufficient. All we
have is a) online everything MOVABLE (online_movable) b) online everything
!MOVABLE (online_kernel) c) keep zones contiguous (online). This series
allows configuring c) to mean instead "online movable if possible according
to the coniguration, driven by a maximum MOVABLE:KERNEL ratio" -- a new
onlining policy.


II. Approach

This series does 3 things:

 1) Introduces the "auto-movable" online policy that initially
operates on
    individual memory blocks only. It uses a maximum MOVABLE:KERNEL ratio
    to make a decision whether a memory block will be onlined to
    ZONE_MOVABLE or not. However, in the basic form, hotplugged KERNEL
    memory does not allow for more MOVABLE memory (details in the
    patches). CMA memory is treated like MOVABLE memory.

 2) Introduces static (e.g., DIMM) and dynamic (e.g., virtio-mem) memory
    groups and uses group information to make decisions in the
    "auto-movable" online policy accross memory blocks of a single
memory
    device (modeled as memory group). More details can be found in patch
    #3 or in the DIMM example below.

 3) Maximizes ZONE_MOVABLE memory within dynamic memory groups, by
    allowing ZONE_NORMAL memory within a dynamic memory group to allow for
    more ZONE_MOVABLE memory within the same memory group. The target use
    case is dynamic VM resizing using virtio-mem. See the virtio-mem
    example below.

I remember that the basic idea of using a ratio to implement a policy in
the kernel was once mentioned by Vitaly Kuznetsov, but I might be wrong
(I lost the pointer to that discussion).

For me, the main use case is using it along with virtio-mem (and
DIMMs / ppc64 dlpar where necessary) for dynamic resizing of VMs,
increasing the amount of memory we can hotunplug reliably again if we
might eventually hotplug a lot of memory to a VM.


III. Target Usage

The target usage will be:

 1) Linux boots with "mhp_default_online_type=offline"

 2) User space (e.g., systemd unit) configures memory onlining (according
    to a config file and system properties), for example:
    * Setting memory_hotplug.online_policy=auto-movable
    * Setting memory_hotplug.auto_movable_ratio=301
    * Setting memory_hotplug.auto_movable_numa_aware=true

 3) User space enabled auto onlining via "echo online >
    /sys/devices/system/memory/auto_online_blocks"

 4) User space triggers manual onlining of all already-offline memory
    blocks (go over offline memory blocks and set them to "online")


IV. Example

For DIMMs, hotplugging 4 GiB DIMMs to a 4 GiB VM with a configured ratio of
301% results in the following layout:
	Memory block 0-15:    DMA32   (early)
	Memory block 32-47:   Normal  (early)
	Memory block 48-79:   Movable (DIMM 0)
	Memory block 80-111:  Movable (DIMM 1)
	Memory block 112-143: Movable (DIMM 2)
	Memory block 144-275: Normal  (DIMM 3)
	Memory block 176-207: Normal  (DIMM 4)
	... all Normal
	(-> hotplugged Normal memory does not allow for more Movable memory)

For virtio-mem, using a simple, single virtio-mem device with a 4 GiB VM
will result in the following layout:
	Memory block 0-15:    DMA32   (early)
	Memory block 32-47:   Normal  (early)
	Memory block 48-143:  Movable (virtio-mem, first 12 GiB)
	Memory block 144:     Normal  (virtio-mem, next 128 MiB)
	Memory block 145-147: Movable (virtio-mem, next 384 MiB)
	Memory block 148:     Normal  (virtio-mem, next 128 MiB)
	Memory block 149-151: Movable (virtio-mem, next 384 MiB)
	... Normal/Movable mixture as above
	(-> hotplugged Normal memory allows for more Movable memory within
	    the same device)

Which gives us maximum flexibility when dynamically growing/shrinking a
VM in smaller steps.


V. Doc Update

I'll update the memory-hotplug.rst documentation, once the overhaul [1] is
usptream. Until then, details can be found in patch #2.


VI. Future Work

 1) Use memory groups for ppc64 dlpar
 2) Being able to specify a portion of (early) kernel memory that will be
    excluded from the ratio. Like "128 MiB globally/per node" are
excluded.

    This might be helpful when starting VMs with extremely small memory
    footprint (e.g., 128 MiB) and hotplugging memory later -- not wanting
    the first hotplugged units getting onlined to ZONE_MOVABLE. One
    alternative would be a trigger to not consider ZONE_DMA memory
    in the ratio. We'll have to see if this is really rrequired.
 3) Indicate to user space that MOVABLE might be a bad idea -- especially
    relevant when memory ballooning without support for balloon compaction
    is active.


v1 -> v2:
- Split out all cleanup patches into [2]
- Minor patch description updates
- "dax/kmem: use a single static memory group for a single probed
unit"
-- Added

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vitaly Kuznetsov <vkuznets at redhat.com>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Jason Wang <jasowang at redhat.com>
Cc: Marek Kedzierski <mkedzier at redhat.com>
Cc: Hui Zhu <teawater at gmail.com>
Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
Cc: Wei Yang <richard.weiyang at linux.alibaba.com>
Cc: Oscar Salvador <osalvador at suse.de>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Mike Rapoport <rppt at kernel.org>
Cc: "Rafael J. Wysocki" <rjw at rjwysocki.net>
Cc: Len Brown <lenb at kernel.org>
Cc: Pavel Tatashin <pasha.tatashin at soleen.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: virtualization at lists.linux-foundation.org
Cc: linux-mm at kvack.org
Cc: linux-acpi at vger.kernel.org

[1] https://lkml.kernel.org/r/20210707073205.3835-1-david at redhat.com
[2] https://lkml.kernel.org/r/20210712124052.26491-1-david at redhat.com

David Hildenbrand (9):
  mm: track present early pages per zone
  mm/memory_hotplug: introduce "auto-movable" online policy
  drivers/base/memory: introduce "memory groups" to logically group
    memory blocks
  mm/memory_hotplug: track present pages in memory groups
  ACPI: memhotplug: use a single static memory group for a single memory
    device
  dax/kmem: use a single static memory group for a single probed unit
  virtio-mem: use a single dynamic memory group for a single virtio-mem
    device
  mm/memory_hotplug: memory group aware "auto-movable" online policy
  mm/memory_hotplug: improved dynamic memory group aware
"auto-movable"
    online policy

 drivers/acpi/acpi_memhotplug.c |  35 +++-
 drivers/base/memory.c          | 163 ++++++++++++++---
 drivers/dax/kmem.c             |  40 +++-
 drivers/virtio/virtio_mem.c    |  22 ++-
 include/linux/memory.h         |  53 +++++-
 include/linux/memory_hotplug.h |  22 ++-
 include/linux/mmzone.h         |   7 +
 mm/memory_hotplug.c            | 323 ++++++++++++++++++++++++++++++++-
 mm/page_alloc.c                |   3 +
 9 files changed, 617 insertions(+), 51 deletions(-)

-- 
2.31.1

For implementing a new memory onlining policy, which determines when to
online memory blocks to ZONE_MOVABLE semi-automatically, we need the number
of present early (boot) pages -- present pages excluding hotplugged pages.
Let's track these pages per zone.

Pass a page instead of the zone to adjust_present_page_count(), similar
as adjust_managed_page_count() and derive the zone from the page.

It's worth noting that a memory block to be offlined/onlined is either
completely "early" or "not early". add_memory() and friends
can only add
complete memory blocks and we only online/offline complete (individual)
memory blocks.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/base/memory.c          | 14 +++++++-------
 include/linux/memory_hotplug.h |  2 +-
 include/linux/mmzone.h         |  7 +++++++
 mm/memory_hotplug.c            | 14 +++++++++++---
 mm/page_alloc.c                |  3 +++
 5 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index aa31a21f33d7..86ec2dc82fc2 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -205,7 +205,8 @@ static int memory_block_online(struct memory_block *mem)
 	 * now already properly populated.
 	 */
 	if (nr_vmemmap_pages)
-		adjust_present_page_count(zone, nr_vmemmap_pages);
+		adjust_present_page_count(pfn_to_page(start_pfn),
+					  nr_vmemmap_pages);
 
 	return ret;
 }
@@ -215,24 +216,23 @@ static int memory_block_offline(struct memory_block *mem)
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	unsigned long nr_vmemmap_pages = mem->nr_vmemmap_pages;
-	struct zone *zone;
 	int ret;
 
 	/*
 	 * Unaccount before offlining, such that unpopulated zone and kthreads
 	 * can properly be torn down in offline_pages().
 	 */
-	if (nr_vmemmap_pages) {
-		zone = page_zone(pfn_to_page(start_pfn));
-		adjust_present_page_count(zone, -nr_vmemmap_pages);
-	}
+	if (nr_vmemmap_pages)
+		adjust_present_page_count(pfn_to_page(start_pfn),
+					  -nr_vmemmap_pages);
 
 	ret = offline_pages(start_pfn + nr_vmemmap_pages,
 			    nr_pages - nr_vmemmap_pages);
 	if (ret) {
 		/* offline_pages() failed. Account back. */
 		if (nr_vmemmap_pages)
-			adjust_present_page_count(zone, nr_vmemmap_pages);
+			adjust_present_page_count(pfn_to_page(start_pfn),
+						  nr_vmemmap_pages);
 		return ret;
 	}
 
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 068e3dcf4690..39b04e99a30e 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -95,7 +95,7 @@ static inline void zone_seqlock_init(struct zone *zone)
 extern int zone_grow_free_lists(struct zone *zone, unsigned long new_nr_pages);
 extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
 extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
-extern void adjust_present_page_count(struct zone *zone, long nr_pages);
+extern void adjust_present_page_count(struct page *page, long nr_pages);
 /* VM interface that may be used by firmware interface */
 extern int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 				     struct zone *zone);
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fcb535560028..6fbe59702bf2 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -540,6 +540,10 @@ struct zone {
 	 * is calculated as:
 	 *	present_pages = spanned_pages - absent_pages(pages in holes);
 	 *
+	 * present_early_pages is present pages existing within the zone
+	 * located on memory available since early boot, excluding hotplugged
+	 * memory.
+	 *
 	 * managed_pages is present pages managed by the buddy system, which
 	 * is calculated as (reserved_pages includes pages allocated by the
 	 * bootmem allocator):
@@ -572,6 +576,9 @@ struct zone {
 	atomic_long_t		managed_pages;
 	unsigned long		spanned_pages;
 	unsigned long		present_pages;
+#if defined(CONFIG_MEMORY_HOTPLUG)
+	unsigned long		present_early_pages;
+#endif
 #ifdef CONFIG_CMA
 	unsigned long		cma_pages;
 #endif
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 388c8627f17f..65dbb30f81c2 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -724,8 +724,16 @@ struct zone *zone_for_pfn_range(int online_type, int nid,
  * This function should only be called by memory_block_{online,offline},
  * and {online,offline}_pages.
  */
-void adjust_present_page_count(struct zone *zone, long nr_pages)
+void adjust_present_page_count(struct page *page, long nr_pages)
 {
+	struct zone *zone = page_zone(page);
+
+	/*
+	 * We only support onlining/offlining/adding/removing of complete
+	 * memory blocks; therefore, either all is either early or hotplugged.
+	 */
+	if (early_section(__pfn_to_section(page_to_pfn(page))))
+		zone->present_early_pages += nr_pages;
 	zone->present_pages += nr_pages;
 	zone->zone_pgdat->node_present_pages += nr_pages;
 }
@@ -826,7 +834,7 @@ int __ref online_pages(unsigned long pfn, unsigned long
nr_pages, struct zone *z
 	}
 
 	online_pages_range(pfn, nr_pages);
-	adjust_present_page_count(zone, nr_pages);
+	adjust_present_page_count(pfn_to_page(pfn), nr_pages);
 
 	node_states_set_node(nid, &arg);
 	if (need_zonelists_rebuild)
@@ -1704,7 +1712,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned
long nr_pages)
 
 	/* removal success */
 	adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
-	adjust_present_page_count(zone, -nr_pages);
+	adjust_present_page_count(pfn_to_page(start_pfn), -nr_pages);
 
 	/* reinitialise watermarks and update pcp limits */
 	init_per_zone_wmark_min();
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3e97e68aef7a..213728db3c01 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7255,6 +7255,9 @@ static void __init calculate_node_totalpages(struct
pglist_data *pgdat,
 			zone->zone_start_pfn = 0;
 		zone->spanned_pages = size;
 		zone->present_pages = real_size;
+#if defined(CONFIG_MEMORY_HOTPLUG)
+		zone->present_early_pages = real_size;
+#endif
 
 		totalpages += size;
 		realtotalpages += real_size;
-- 
2.31.1

When onlining without specifying a zone (using "online" instead of
"online_kernel" or "online_movable"), we currently select a
zone such that
existing zones are kept contiguous. This online policy made sense in the
past, where contiguous zones where required.

We'd like to implement smarter policies, however:

* User space has little insight. As one example, it has no idea which
  memory blocks logically belong together (e.g., to a DIMM or to a
  virtio-mem device).
* Drivers that add memory in separate memory blocks, especially
  virtio-mem, want memory to get onlined right from the kernel when
  adding.

So we really want to have onlining to differing zones managed in the
kernel, configured by user space.

We see more and more cases where we might eventually hotplug a lot of
memory in the future (e.g., eventually grow a 2 GiB VM to 64 GiB), however:

* Resizing happens dynamically, in smaller steps in both directions
  (e.g., 2 GiB -> 8 GiB -> 4 GiB -> 16 GiB ...)
* We still want as much flexibility as possible, especially,
  hotunplugging as much memory as possible later.

We can really only use "online_movable" if we know that the amount of
memory we are going to hotplug upfront, and we know that it won't result
in a zone imbalance. So in our example, a 2 GiB VM that could grow to 64
GiB could currently not use "online_movable", and instead,
"online_kernel" would have to be used, resulting in worse (no) memory
hotunplug reliability.

Let's add a new "auto-movable" online policy that considers the
current
zone ratios (global, per-node) to determine, whether we a memory block
can be onlined to ZONE_MOVABLE:

	MOVABLE : KERNEL

However, internally we'll only consider the following ratio for now:

	MOVABLE : KERNEL_EARLY

For now, we don't allow for hotplugged KERNEL memory to allow for more
MOVABLE memory, because there is no coordination across memory devices.
In follow-up patches, we will allow for more KERNEL memory within a memory
device to allow for more MOVABLE memory within the same memory device --
which only makes sense for special memory device types.

We base our calculation on "present pages", see the code comments for
details. Hotplugged memory will get online to ZONE_MOVABLE if the
configured ratio allows for it. Depending on the setup, this can result
in fragmented zones, which can make compaction slower and dynamic
allocation of gigantic pages when not using CMA less reliable
(... which is already pretty unreliable).

The old policy will be the default and called "contig-zones". In
follow-up
patches, our new policy will use additional information, such as memory
groups, to make even smarter decisions across memory blocks.

Configuration:

* memory_hotplug.online_policy is used to switch between both polices and
  defaults to "contig-zones".
* memory_hotplug.auto_movable_ratio defines the maximum ratio is in percent
  and defaults to "301" -- allowing e.g., most 8 GiB machines to grow
to 32
  GiB and have all hotplugged memory in ZONE_MOVABLE. The additional
  percent accounts for a handful of lost present pages (e.g., firmware
  allocations). User space is expected to adjust this ratio when enabling
  the new "auto-movable" policy, though.
* memory_hotplug.auto_movable_numa_aware considers numa node stats in
  addition to global stats, and defaults to "true".

Note: just like the old policy, the new policy won't take things like
unmovable huge pages or memory ballooning that doesn't support balloon
compaction into account. User space has to configure onlining
accordingly.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 mm/memory_hotplug.c | 189 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 189 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 65dbb30f81c2..f50bb720f7fc 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -52,6 +52,73 @@ module_param(memmap_on_memory, bool, 0444);
 MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory
hotplug");
 #endif
 
+enum {
+	ONLINE_POLICY_CONTIG_ZONES = 0,
+	ONLINE_POLICY_AUTO_MOVABLE,
+};
+
+const char *online_policy_to_str[] = {
+	[ONLINE_POLICY_CONTIG_ZONES] = "contig-zones",
+	[ONLINE_POLICY_AUTO_MOVABLE] = "auto-movable",
+};
+
+static int set_online_policy(const char *val, const struct kernel_param *kp)
+{
+	int ret = sysfs_match_string(online_policy_to_str, val);
+
+	if (ret < 0)
+		return ret;
+	*((int *)kp->arg) = ret;
+	return 0;
+}
+
+static int get_online_policy(char *buffer, const struct kernel_param *kp)
+{
+	return sprintf(buffer, "%s\n", online_policy_to_str[*((int
*)kp->arg)]);
+}
+
+/*
+ * memory_hotplug.online_policy: configure online behavior when onlining
without
+ * specifying a zone (MMOP_ONLINE)
+ *
+ * "contig-zones": keep zone contiguous
+ * "auto-movable": online memory to ZONE_MOVABLE if the configuration
+ *                 (auto_movable_ratio, auto_movable_numa_aware) allows for it
+ */
+static int online_policy __read_mostly = ONLINE_POLICY_CONTIG_ZONES;
+static const struct kernel_param_ops online_policy_ops = {
+	.set = set_online_policy,
+	.get = get_online_policy,
+};
+module_param_cb(online_policy, &online_policy_ops, &online_policy,
0644);
+MODULE_PARM_DESC(online_policy,
+		"Set the online policy (\"contig-zones\",
\"auto-movable\") "
+		"Default: \"contig-zones\"");
+
+/*
+ * memory_hotplug.auto_movable_ratio: specify maximum MOVABLE:KERNEL ratio
+ *
+ * The ratio represent an upper limit and the kernel might decide to not
+ * online some memory to ZONE_MOVABLE -- e.g., because hotplugged KERNEL memory
+ * doesn't allow for more MOVABLE memory.
+ */
+static unsigned int auto_movable_ratio __read_mostly = 301;
+module_param(auto_movable_ratio, uint, 0644);
+MODULE_PARM_DESC(auto_movable_ratio,
+		"Set the maximum ratio of MOVABLE:KERNEL memory in the system "
+		"in percent for \"auto-movable\" online policy. Default:
301");
+
+/*
+ * memory_hotplug.auto_movable_numa_aware: consider numa node stats
+ */
+#ifdef CONFIG_NUMA
+static bool auto_movable_numa_aware __read_mostly = true;
+module_param(auto_movable_numa_aware, bool, 0644);
+MODULE_PARM_DESC(auto_movable_numa_aware,
+		"Consider numa node stats in addition to global stats in "
+		"\"auto-movable\" online policy. Default: true");
+#endif /* CONFIG_NUMA */
+
 /*
  * online_page_callback contains pointer to current page onlining function.
  * Initially it is generic_online_page(). If it is required it could be
@@ -663,6 +730,59 @@ void __ref move_pfn_range_to_zone(struct zone *zone,
unsigned long start_pfn,
 	set_zone_contiguous(zone);
 }
 
+struct auto_movable_stats {
+	unsigned long kernel_early_pages;
+	unsigned long movable_pages;
+};
+
+static void auto_movable_stats_account_zone(struct auto_movable_stats *stats,
+					    struct zone *zone)
+{
+	if (zone_idx(zone) == ZONE_MOVABLE) {
+		stats->movable_pages += zone->present_pages;
+	} else {
+		/*
+		 * CMA pages (never on hotplugged memory) behave like
+		 * ZONE_MOVABLE.
+		 */
+		stats->movable_pages += zone->cma_pages;
+		stats->kernel_early_pages += zone->present_early_pages;
+		stats->kernel_early_pages -= zone->cma_pages;
+	}
+}
+
+static bool auto_movable_can_online_movable(int nid, unsigned long nr_pages)
+{
+	struct auto_movable_stats stats = {};
+	unsigned long kernel_early_pages, movable_pages;
+	pg_data_t *pgdat = NODE_DATA(nid);
+	struct zone *zone;
+	int i;
+
+	/* Walk all relevant zones and collect MOVABLE vs. KERNEL stats. */
+	if (nid == NUMA_NO_NODE) {
+		/* TODO: cache values */
+		for_each_populated_zone(zone)
+			auto_movable_stats_account_zone(&stats, zone);
+	} else {
+		for (i = 0; i < MAX_NR_ZONES; i++) {
+			zone = pgdat->node_zones + i;
+			if (populated_zone(zone))
+				auto_movable_stats_account_zone(&stats, zone);
+		}
+	}
+
+	kernel_early_pages = stats.kernel_early_pages;
+	movable_pages = stats.movable_pages;
+
+	/*
+	 * Test if we could online the given number of pages to ZONE_MOVABLE
+	 * and still stay in the configured ratio.
+	 */
+	movable_pages += nr_pages;
+	return movable_pages <= (auto_movable_ratio * kernel_early_pages) / 100;
+}
+
 /*
  * Returns a default kernel memory zone for the given pfn range.
  * If no kernel zone covers this pfn range it will automatically go
@@ -684,6 +804,72 @@ static struct zone *default_kernel_zone_for_pfn(int nid,
unsigned long start_pfn
 	return &pgdat->node_zones[ZONE_NORMAL];
 }
 
+/*
+ * Determine to which zone to online memory dynamically based on user
+ * configuration and system stats. We care about the following ratio:
+ *
+ *   MOVABLE : KERNEL
+ *
+ * Whereby MOVABLE is memory in ZONE_MOVABLE and KERNEL is memory in
+ * one of the kernel zones. CMA pages inside one of the kernel zones really
+ * behaves like ZONE_MOVABLE, so we treat them accordingly.
+ *
+ * We don't allow for hotplugged memory in a KERNEL zone to increase the
+ * amount of MOVABLE memory we can have, so we end up with:
+ *
+ *   MOVABLE : KERNEL_EARLY
+ *
+ * Whereby KERNEL_EARLY is memory in one of the kernel zones, available sinze
+ * boot. We base our calculation on KERNEL_EARLY internally, because:
+ *
+ * a) Hotplugged memory in one of the kernel zones can sometimes still get
+ *    hotunplugged, especially when hot(un)plugging individual memory blocks.
+ *    There is no coordination across memory devices, therefore
"automatic"
+ *    hotunplugging, as implemented in hypervisors, could result in zone
+ *    imbalances.
+ * b) Early/boot memory in one of the kernel zones can usually not get
+ *    hotunplugged again (e.g., no firmware interface to unplug, fragmented
+ *    with unmovable allocations). While there are corner cases where it might
+ *    still work, it is barely relevant in practice.
+ *
+ * We rely on "present pages" instead of "managed pages",
as the latter is
+ * highly unreliable and dynamic in virtualized environments, and does not
+ * consider boot time allocations. For example, memory ballooning adjusts the
+ * managed pages when inflating/deflating the balloon, and balloon compaction
+ * can even migrate inflated pages between zones.
+ *
+ * Using "present pages" is better but some things to keep in mind
are:
+ *
+ * a) Some memblock allocations, such as for the crashkernel area, are
+ *    effectively unused by the kernel, yet they account to "present
pages".
+ *    Fortunately, these allocations are comparatively small in relevant setups
+ *    (e.g., fraction of system memory).
+ * b) Some hotplugged memory blocks in virtualized environments, esecially
+ *    hotplugged by virtio-mem, look like they are completely present, however,
+ *    only parts of the memory block are actually currently usable.
+ *    "present pages" is an upper limit that can get reached at
runtime. As
+ *    we base our calculations on KERNEL_EARLY, this is not an issue.
+ */
+static struct zone *auto_movable_zone_for_pfn(int nid, unsigned long pfn,
+					      unsigned long nr_pages)
+{
+	if (!auto_movable_ratio)
+		goto kernel_zone;
+
+	if (!auto_movable_can_online_movable(NUMA_NO_NODE, nr_pages))
+		goto kernel_zone;
+
+#ifdef CONFIG_NUMA
+	if (auto_movable_numa_aware &&
+	    !auto_movable_can_online_movable(nid, nr_pages))
+		goto kernel_zone;
+#endif /* CONFIG_NUMA */
+
+	return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
+kernel_zone:
+	return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
+}
+
 static inline struct zone *default_zone_for_pfn(int nid, unsigned long
start_pfn,
 		unsigned long nr_pages)
 {
@@ -717,6 +903,9 @@ struct zone *zone_for_pfn_range(int online_type, int nid,
 	if (online_type == MMOP_ONLINE_MOVABLE)
 		return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
 
+	if (online_policy == ONLINE_POLICY_AUTO_MOVABLE)
+		return auto_movable_zone_for_pfn(nid, start_pfn, nr_pages);
+
 	return default_zone_for_pfn(nid, start_pfn, nr_pages);
 }
 
-- 
2.31.1

In our "auto-movable" memory onlining policy, we want to make
decisions
across memory blocks of a single memory device. Examples of memory devices
include ACPI memory devices (in the simplest case a single DIMM) and
virtio-mem. For now, we don't have a connection between a single memory
block device and the real memory device. Each memory device consists of
1..X memory block devices.

Let's logically group memory blocks belonging to the same memory device
in "memory groups". Memory groups can span multiple physical ranges
and a
memory group itself does not contain any information regarding physical
ranges, only properties (e.g., "max_pages") necessary for improved
memory
onlining.

Introduce two memory group types:

1) Static memory group: E.g., a single ACPI memory device, consisting of
   1..X memory resources. A memory group consists of 1..Y memory blocks.
   The whole group is added/removed in one go. If any part cannot get
   offlined, the whole group cannot be removed.

2) Dynamic memory group: E.g., a single virtio-mem device. Memory is
   dynamically added/removed in a fixed granularity, called a "unit",
   consisting of 1..X memory blocks. A unit is added/removed in one go.
   If any part of a unit cannot get offlined, the whole unit cannot be
   removed.

In case of 1) we usually want either all memory managed by ZONE_MOVABLE
or none. In case of 2) we usually want to have as many units as possible
managed by ZONE_MOVABLE. We want a single unit to be of the same type.

For now, memory groups are an internal concept that is not exposed to
user space; we might want to change that in the future, though.

add_memory() users can specify a mgid instead of a nid when passing
the MHP_NID_IS_MGID flag.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/base/memory.c          | 102 +++++++++++++++++++++++++++++++--
 include/linux/memory.h         |  46 ++++++++++++++-
 include/linux/memory_hotplug.h |   6 +-
 mm/memory_hotplug.c            |  11 +++-
 4 files changed, 158 insertions(+), 7 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 86ec2dc82fc2..42109e7fb0b5 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -82,6 +82,11 @@ static struct bus_type memory_subsys = {
  */
 static DEFINE_XARRAY(memory_blocks);
 
+/*
+ * Memory groups, indexed by memory group identification (mgid).
+ */
+static DEFINE_XARRAY_FLAGS(memory_groups, XA_FLAGS_ALLOC);
+
 static BLOCKING_NOTIFIER_HEAD(memory_chain);
 
 int register_memory_notifier(struct notifier_block *nb)
@@ -634,7 +639,8 @@ int register_memory(struct memory_block *memory)
 }
 
 static int init_memory_block(unsigned long block_id, unsigned long state,
-			     unsigned long nr_vmemmap_pages)
+			     unsigned long nr_vmemmap_pages,
+			     struct memory_group *group)
 {
 	struct memory_block *mem;
 	int ret = 0;
@@ -653,6 +659,11 @@ static int init_memory_block(unsigned long block_id,
unsigned long state,
 	mem->nid = NUMA_NO_NODE;
 	mem->nr_vmemmap_pages = nr_vmemmap_pages;
 
+	if (group) {
+		mem->group = group;
+		refcount_inc(&group->refcount);
+	}
+
 	ret = register_memory(mem);
 
 	return ret;
@@ -671,7 +682,7 @@ static int add_memory_block(unsigned long base_section_nr)
 	if (section_count == 0)
 		return 0;
 	return init_memory_block(memory_block_id(base_section_nr),
-				 MEM_ONLINE, 0);
+				 MEM_ONLINE, 0,  NULL);
 }
 
 static void unregister_memory(struct memory_block *memory)
@@ -681,6 +692,11 @@ static void unregister_memory(struct memory_block *memory)
 
 	WARN_ON(xa_erase(&memory_blocks, memory->dev.id) == NULL);
 
+	if (memory->group) {
+		refcount_dec(&memory->group->refcount);
+		memory->group = NULL;
+	}
+
 	/* drop the ref. we got via find_memory_block() */
 	put_device(&memory->dev);
 	device_unregister(&memory->dev);
@@ -694,7 +710,8 @@ static void unregister_memory(struct memory_block *memory)
  * Called under device_hotplug_lock.
  */
 int create_memory_block_devices(unsigned long start, unsigned long size,
-				unsigned long vmemmap_pages)
+				unsigned long vmemmap_pages,
+				struct memory_group *group)
 {
 	const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
 	unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
@@ -707,7 +724,8 @@ int create_memory_block_devices(unsigned long start,
unsigned long size,
 		return -EINVAL;
 
 	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
-		ret = init_memory_block(block_id, MEM_OFFLINE, vmemmap_pages);
+		ret = init_memory_block(block_id, MEM_OFFLINE, vmemmap_pages,
+					group);
 		if (ret)
 			break;
 	}
@@ -891,3 +909,79 @@ int for_each_memory_block(void *arg,
walk_memory_blocks_func_t func)
 	return bus_for_each_dev(&memory_subsys, NULL, &cb_data,
 				for_each_memory_block_cb);
 }
+
+static int register_memory_group(struct memory_group group)
+{
+	struct memory_group *new_group;
+	uint32_t mgid;
+	int ret;
+
+	if (!node_possible(group.nid))
+		return -EINVAL;
+
+	new_group = kzalloc(sizeof(group), GFP_KERNEL);
+	if (!new_group)
+		return -ENOMEM;
+	*new_group = group;
+	refcount_set(&new_group->refcount, 1);
+
+	ret = xa_alloc(&memory_groups, &mgid, new_group, xa_limit_31b,
+		       GFP_KERNEL);
+	if (ret)
+		kfree(new_group);
+	return ret ? ret : mgid;
+}
+
+int register_static_memory_group(int nid, unsigned long max_pages)
+{
+	struct memory_group group = {
+		.nid = nid,
+		.s = {
+			.max_pages = max_pages,
+		},
+	};
+
+	if (!max_pages)
+		return -EINVAL;
+	return register_memory_group(group);
+}
+EXPORT_SYMBOL_GPL(register_static_memory_group);
+
+int register_dynamic_memory_group(int nid, unsigned long unit_pages)
+{
+	struct memory_group group = {
+		.nid = nid,
+		.is_dynamic = true,
+		.d = {
+			.unit_pages = unit_pages,
+		},
+	};
+
+	if (!unit_pages || !is_power_of_2(unit_pages) ||
+	    unit_pages < PHYS_PFN(memory_block_size_bytes()))
+		return -EINVAL;
+	return register_memory_group(group);
+}
+EXPORT_SYMBOL_GPL(register_dynamic_memory_group);
+
+int unregister_memory_group(int mgid)
+{
+	struct memory_group *group;
+
+	if (mgid < 0)
+		return -EINVAL;
+
+	group = xa_load(&memory_groups, mgid);
+	if (!group || refcount_read(&group->refcount) > 1)
+		return -EINVAL;
+
+	xa_erase(&memory_groups, mgid);
+	kfree(group);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unregister_memory_group);
+
+struct memory_group *get_memory_group(int mgid)
+{
+	return xa_load(&memory_groups, mgid);
+}
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 97e92e8b556a..6e20a6174fe5 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -23,6 +23,42 @@
 
 #define MIN_MEMORY_BLOCK_SIZE     (1UL << SECTION_SIZE_BITS)
 
+struct memory_group {
+	/* Nid the whole group belongs to. */
+	int nid;
+	/* References from memory blocks + 1. */
+	refcount_t refcount;
+	/*
+	 * Memory group type: static vs. dynamic.
+	 *
+	 * Static: All memory in the group belongs to a single unit, such as,
+	 * a DIMM. All memory belonging to the group will be added in
+	 * one go and removed in one go -- it's static.
+	 *
+	 * Dynamic: Memory within the group is added/removed dynamically in
+	 * units of the specified granularity of at least one memory block.
+	 */
+	bool is_dynamic;
+
+	union {
+		struct {
+			/*
+			 * Maximum number of pages we'll have in this static
+			 * memory group.
+			 */
+			unsigned long max_pages;
+		} s;
+		struct {
+			/*
+			 * Unit in pages in which memory is added/removed in
+			 * this dynamic memory group. This granularity defines
+			 * the alignment of a unit in physical address space.
+			 */
+			unsigned long unit_pages;
+		} d;
+	};
+};
+
 struct memory_block {
 	unsigned long start_section_nr;
 	unsigned long state;		/* serialized by the dev->lock */
@@ -34,6 +70,7 @@ struct memory_block {
 	 * lay at the beginning of the memory block.
 	 */
 	unsigned long nr_vmemmap_pages;
+	struct memory_group *group;	/* group (if any) for this block */
 };
 
 int arch_get_memory_phys_device(unsigned long start_pfn);
@@ -86,7 +123,8 @@ static inline int memory_notify(unsigned long val, void *v)
 extern int register_memory_notifier(struct notifier_block *nb);
 extern void unregister_memory_notifier(struct notifier_block *nb);
 int create_memory_block_devices(unsigned long start, unsigned long size,
-				unsigned long vmemmap_pages);
+				unsigned long vmemmap_pages,
+				struct memory_group *group);
 void remove_memory_block_devices(unsigned long start, unsigned long size);
 extern void memory_dev_init(void);
 extern int memory_notify(unsigned long val, void *v);
@@ -95,6 +133,12 @@ typedef int (*walk_memory_blocks_func_t)(struct memory_block
*, void *);
 extern int walk_memory_blocks(unsigned long start, unsigned long size,
 			      void *arg, walk_memory_blocks_func_t func);
 extern int for_each_memory_block(void *arg, walk_memory_blocks_func_t func);
+
+extern int register_static_memory_group(int nid, unsigned long max_pages);
+extern int register_dynamic_memory_group(int nid, unsigned long unit_pages);
+extern int unregister_memory_group(int mgid);
+struct memory_group *get_memory_group(int mgid);
+
 #define CONFIG_MEM_BLOCK_SIZE	(PAGES_PER_SECTION<<PAGE_SHIFT)
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
 
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 39b04e99a30e..5beb65497ae3 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -42,7 +42,6 @@ typedef int __bitwise mhp_t;
  * might be stale, or the resource might have changed.
  */
 #define MHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
-
 /*
  * We want memmap (struct page array) to be self contained.
  * To do so, we will use the beginning of the hot-added range to build
@@ -50,6 +49,11 @@ typedef int __bitwise mhp_t;
  * Only selected architectures support it with SPARSE_VMEMMAP.
  */
 #define MHP_MEMMAP_ON_MEMORY   ((__force mhp_t)BIT(1))
+/*
+ * The nid field specifies a memory group identifier (mgid) instead. The memory
+ * group implies the nid.
+ */
+#define MHP_NID_IS_MGID		((__force mhp_t)BIT(2))
 
 /*
  * Extended parameters for memory hotplug:
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index f50bb720f7fc..b091d21d8796 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1256,6 +1256,7 @@ int __ref add_memory_resource(int nid, struct resource
*res, mhp_t mhp_flags)
 {
 	struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
 	struct vmem_altmap mhp_altmap = {};
+	struct memory_group *group = NULL;
 	u64 start, size;
 	bool new_node = false;
 	int ret;
@@ -1267,6 +1268,13 @@ int __ref add_memory_resource(int nid, struct resource
*res, mhp_t mhp_flags)
 	if (ret)
 		return ret;
 
+	if (mhp_flags & MHP_NID_IS_MGID) {
+		group = get_memory_group(nid);
+		if (!group)
+			return -EINVAL;
+		nid = group->nid;
+	}
+
 	if (!node_possible(nid)) {
 		WARN(1, "node %d was absent from the node_possible_map\n", nid);
 		return -EINVAL;
@@ -1301,7 +1309,8 @@ int __ref add_memory_resource(int nid, struct resource
*res, mhp_t mhp_flags)
 		goto error;
 
 	/* create memory block devices after memory was added */
-	ret = create_memory_block_devices(start, size, mhp_altmap.alloc);
+	ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
+					  group);
 	if (ret) {
 		arch_remove_memory(start, size, NULL);
 		goto error;
-- 
2.31.1

Let's track all present pages in each memory group. Especially, track
memory present in ZONE_MOVABLE and memory present in one of the kernel
zones (which really only is ZONE_NORMAL right now as memory groups only
apply to hotplugged memory) separately within a memory group, to prepare
for making smart auto-online decision for individual memory blocks within a
memory group based on group statistics.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/base/memory.c          | 10 +++++-----
 include/linux/memory.h         |  4 ++++
 include/linux/memory_hotplug.h | 13 +++++++++----
 mm/memory_hotplug.c            | 19 ++++++++++++++-----
 4 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 42109e7fb0b5..e96c4f436ac3 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -198,7 +198,7 @@ static int memory_block_online(struct memory_block *mem)
 	}
 
 	ret = online_pages(start_pfn + nr_vmemmap_pages,
-			   nr_pages - nr_vmemmap_pages, zone);
+			   nr_pages - nr_vmemmap_pages, zone, mem->group);
 	if (ret) {
 		if (nr_vmemmap_pages)
 			mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
@@ -210,7 +210,7 @@ static int memory_block_online(struct memory_block *mem)
 	 * now already properly populated.
 	 */
 	if (nr_vmemmap_pages)
-		adjust_present_page_count(pfn_to_page(start_pfn),
+		adjust_present_page_count(pfn_to_page(start_pfn), mem->group,
 					  nr_vmemmap_pages);
 
 	return ret;
@@ -228,16 +228,16 @@ static int memory_block_offline(struct memory_block *mem)
 	 * can properly be torn down in offline_pages().
 	 */
 	if (nr_vmemmap_pages)
-		adjust_present_page_count(pfn_to_page(start_pfn),
+		adjust_present_page_count(pfn_to_page(start_pfn), mem->group,
 					  -nr_vmemmap_pages);
 
 	ret = offline_pages(start_pfn + nr_vmemmap_pages,
-			    nr_pages - nr_vmemmap_pages);
+			    nr_pages - nr_vmemmap_pages, mem->group);
 	if (ret) {
 		/* offline_pages() failed. Account back. */
 		if (nr_vmemmap_pages)
 			adjust_present_page_count(pfn_to_page(start_pfn),
-						  nr_vmemmap_pages);
+						  mem->group, nr_vmemmap_pages);
 		return ret;
 	}
 
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 6e20a6174fe5..0eceb8467d9a 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -28,6 +28,10 @@ struct memory_group {
 	int nid;
 	/* References from memory blocks + 1. */
 	refcount_t refcount;
+	/* Present (online) memory outside ZONE_MOVABLE of this memory group. */
+	unsigned long present_kernel_pages;
+	/* Present (online) memory in ZONE_MOVABLE of this memory group. */
+	unsigned long present_movable_pages;
 	/*
 	 * Memory group type: static vs. dynamic.
 	 *
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 5beb65497ae3..23c4d369ad30 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -12,6 +12,7 @@ struct zone;
 struct pglist_data;
 struct mem_section;
 struct memory_block;
+struct memory_group;
 struct resource;
 struct vmem_altmap;
 
@@ -99,13 +100,15 @@ static inline void zone_seqlock_init(struct zone *zone)
 extern int zone_grow_free_lists(struct zone *zone, unsigned long new_nr_pages);
 extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
 extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
-extern void adjust_present_page_count(struct page *page, long nr_pages);
+extern void adjust_present_page_count(struct page *page,
+				      struct memory_group *group,
+				      long nr_pages);
 /* VM interface that may be used by firmware interface */
 extern int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 				     struct zone *zone);
 extern void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long
nr_pages);
 extern int online_pages(unsigned long pfn, unsigned long nr_pages,
-			struct zone *zone);
+			struct zone *zone, struct memory_group *group);
 extern struct zone *test_pages_in_a_zone(unsigned long start_pfn,
 					 unsigned long end_pfn);
 extern void __offline_isolated_pages(unsigned long start_pfn,
@@ -295,7 +298,8 @@ static inline void pgdat_resize_init(struct pglist_data
*pgdat) {}
 #ifdef CONFIG_MEMORY_HOTREMOVE
 
 extern void try_offline_node(int nid);
-extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
+extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+			 struct memory_group *group);
 extern int remove_memory(u64 start, u64 size);
 extern void __remove_memory(u64 start, u64 size);
 extern int offline_and_remove_memory(u64 start, u64 size);
@@ -303,7 +307,8 @@ extern int offline_and_remove_memory(u64 start, u64 size);
 #else
 static inline void try_offline_node(int nid) {}
 
-static inline int offline_pages(unsigned long start_pfn, unsigned long
nr_pages)
+static inline int offline_pages(unsigned long start_pfn, unsigned long
nr_pages,
+				struct memory_group *group)
 {
 	return -EINVAL;
 }
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b091d21d8796..8d556396b5d4 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -913,9 +913,11 @@ struct zone *zone_for_pfn_range(int online_type, int nid,
  * This function should only be called by memory_block_{online,offline},
  * and {online,offline}_pages.
  */
-void adjust_present_page_count(struct page *page, long nr_pages)
+void adjust_present_page_count(struct page *page, struct memory_group *group,
+			       long nr_pages)
 {
 	struct zone *zone = page_zone(page);
+	const bool movable = zone_idx(zone) == ZONE_MOVABLE;
 
 	/*
 	 * We only support onlining/offlining/adding/removing of complete
@@ -925,6 +927,11 @@ void adjust_present_page_count(struct page *page, long
nr_pages)
 		zone->present_early_pages += nr_pages;
 	zone->present_pages += nr_pages;
 	zone->zone_pgdat->node_present_pages += nr_pages;
+
+	if (group && movable)
+		group->present_movable_pages += nr_pages;
+	else if (group && !movable)
+		group->present_kernel_pages += nr_pages;
 }
 
 int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
@@ -970,7 +977,8 @@ void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned
long nr_pages)
 	kasan_remove_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
 }
 
-int __ref online_pages(unsigned long pfn, unsigned long nr_pages, struct zone
*zone)
+int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
+		       struct zone *zone, struct memory_group *group)
 {
 	unsigned long flags;
 	int need_zonelists_rebuild = 0;
@@ -1023,7 +1031,7 @@ int __ref online_pages(unsigned long pfn, unsigned long
nr_pages, struct zone *z
 	}
 
 	online_pages_range(pfn, nr_pages);
-	adjust_present_page_count(pfn_to_page(pfn), nr_pages);
+	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
 
 	node_states_set_node(nid, &arg);
 	if (need_zonelists_rebuild)
@@ -1774,7 +1782,8 @@ static int count_system_ram_pages_cb(unsigned long
start_pfn,
 	return 0;
 }
 
-int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
+int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+			struct memory_group *group)
 {
 	const unsigned long end_pfn = start_pfn + nr_pages;
 	unsigned long pfn, system_ram_pages = 0;
@@ -1910,7 +1919,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned
long nr_pages)
 
 	/* removal success */
 	adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
-	adjust_present_page_count(pfn_to_page(start_pfn), -nr_pages);
+	adjust_present_page_count(pfn_to_page(start_pfn), group, -nr_pages);
 
 	/* reinitialise watermarks and update pcp limits */
 	init_per_zone_wmark_min();
-- 
2.31.1

Let's group all memory we add for a single memory device - we want a
single node for that (which also seems to be the sane thing to do).

We won't care for now about memory that was already added to the system
(e.g., via e820) -- usually *all* memory of a memory device was already
added and we'll fail acpi_memory_enable_device().

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/acpi/acpi_memhotplug.c | 35 +++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index eb4faf7c5cad..0ffa3db142a1 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -54,6 +54,7 @@ struct acpi_memory_info {
 struct acpi_memory_device {
 	struct acpi_device *device;
 	struct list_head res_list;
+	int mgid;
 };
 
 static acpi_status
@@ -169,12 +170,33 @@ static void acpi_unbind_memory_blocks(struct
acpi_memory_info *info)
 static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
 {
 	acpi_handle handle = mem_device->device->handle;
+	mhp_t mhp_flags = MHP_NID_IS_MGID;
 	int result, num_enabled = 0;
 	struct acpi_memory_info *info;
-	mhp_t mhp_flags = MHP_NONE;
-	int node;
+	u64 total_length = 0;
+	int node, mgid;
 
 	node = acpi_get_node(handle);
+
+	list_for_each_entry(info, &mem_device->res_list, list) {
+		if (!info->length)
+			continue;
+		/* We want a single node for the whole memory group */
+		if (node < 0)
+			node = memory_add_physaddr_to_nid(info->start_addr);
+		total_length += info->length;
+	}
+
+	if (!total_length) {
+		dev_err(&mem_device->device->dev, "device is empty\n");
+		return -EINVAL;
+	}
+
+	mgid = register_static_memory_group(node, PFN_UP(total_length));
+	if (mgid < 0)
+		return mgid;
+	mem_device->mgid = mgid;
+
 	/*
 	 * Tell the VM there is more memory here...
 	 * Note: Assume that this function returns zero on success
@@ -188,12 +210,10 @@ static int acpi_memory_enable_device(struct
acpi_memory_device *mem_device)
 		 */
 		if (!info->length)
 			continue;
-		if (node < 0)
-			node = memory_add_physaddr_to_nid(info->start_addr);
 
 		if (mhp_supports_memmap_on_memory(info->length))
 			mhp_flags |= MHP_MEMMAP_ON_MEMORY;
-		result = __add_memory(node, info->start_addr, info->length,
+		result = __add_memory(mgid, info->start_addr, info->length,
 				      mhp_flags);
 
 		/*
@@ -253,6 +273,10 @@ static void acpi_memory_device_free(struct
acpi_memory_device *mem_device)
 	if (!mem_device)
 		return;
 
+	/* In case we succeeded adding *some* memory, unregistering fails. */
+	if (mem_device->mgid >= 0)
+		unregister_memory_group(mem_device->mgid);
+
 	acpi_memory_free_device_resources(mem_device);
 	mem_device->device->driver_data = NULL;
 	kfree(mem_device);
@@ -273,6 +297,7 @@ static int acpi_memory_device_add(struct acpi_device
*device,
 
 	INIT_LIST_HEAD(&mem_device->res_list);
 	mem_device->device = device;
+	mem_device->mgid = -1;
 	sprintf(acpi_device_name(device), "%s", ACPI_MEMORY_DEVICE_NAME);
 	sprintf(acpi_device_class(device), "%s", ACPI_MEMORY_DEVICE_CLASS);
 	device->driver_data = mem_device;
-- 
2.31.1

Although dax/kmem users often disable auto-onlining and instead online
memory manually (usually to ZONE_MOVABLE), there is still value in
having auto-onlining be aware of the relationship of memory blocks.

Let's treat one probed unit as a single static memory device, similar to
a single ACPI memory device.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/dax/kmem.c | 40 ++++++++++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 99e0f60c4c26..b528f85de845 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -37,15 +37,16 @@ static int dax_kmem_range(struct dev_dax *dev_dax, int i,
struct range *r)
 
 struct dax_kmem_data {
 	const char *res_name;
+	int mgid;
 	struct resource *res[];
 };
 
 static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 {
 	struct device *dev = &dev_dax->dev;
+	unsigned long total_len = 0;
 	struct dax_kmem_data *data;
-	int rc = -ENOMEM;
-	int i, mapped = 0;
+	int i, rc, mapped = 0;
 	int numa_node;
 
 	/*
@@ -61,24 +62,44 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 		return -EINVAL;
 	}
 
+	for (i = 0; i < dev_dax->nr_range; i++) {
+		struct range range;
+
+		rc = dax_kmem_range(dev_dax, i, &range);
+		if (rc) {
+			dev_info(dev, "mapping%d: %#llx-%#llx too small after
alignment\n",
+					i, range.start, range.end);
+			continue;
+		}
+		total_len += range_len(&range);
+	}
+
+	if (!total_len) {
+		dev_warn(dev, "rejecting DAX region without any memory after
alignment\n");
+		return -EINVAL;
+	}
+
 	data = kzalloc(struct_size(data, res, dev_dax->nr_range), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
 
+	rc = -ENOMEM;
 	data->res_name = kstrdup(dev_name(dev), GFP_KERNEL);
 	if (!data->res_name)
 		goto err_res_name;
 
+	rc = register_static_memory_group(numa_node, total_len);
+	if (rc < 0)
+		goto err_reg_mgid;
+	data->mgid = rc;
+
 	for (i = 0; i < dev_dax->nr_range; i++) {
 		struct resource *res;
 		struct range range;
 
 		rc = dax_kmem_range(dev_dax, i, &range);
-		if (rc) {
-			dev_info(dev, "mapping%d: %#llx-%#llx too small after
alignment\n",
-					i, range.start, range.end);
+		if (rc)
 			continue;
-		}
 
 		/* Region is permanently reserved if hotremove fails. */
 		res = request_mem_region(range.start, range_len(&range),
data->res_name);
@@ -108,8 +129,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 		 * Ensure that future kexec'd kernels will not treat
 		 * this as RAM automatically.
 		 */
-		rc = add_memory_driver_managed(numa_node, range.start,
-				range_len(&range), kmem_name, MHP_NONE);
+		rc = add_memory_driver_managed(data->mgid, range.start,
+				range_len(&range), kmem_name, MHP_NID_IS_MGID);
 
 		if (rc) {
 			dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
@@ -129,6 +150,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	return 0;
 
 err_request_mem:
+	unregister_memory_group(data->mgid);
+err_reg_mgid:
 	kfree(data->res_name);
 err_res_name:
 	kfree(data);
@@ -171,6 +194,7 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
 	}
 
 	if (success >= dev_dax->nr_range) {
+		unregister_memory_group(data->mgid);
 		kfree(data->res_name);
 		kfree(data);
 		dev_set_drvdata(dev, NULL);
-- 
2.31.1

Let's use a single dynamic memory group.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/virtio/virtio_mem.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 774986695dc4..19036922f7ef 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -143,6 +143,8 @@ struct virtio_mem {
 	 * add_memory_driver_managed().
 	 */
 	const char *resource_name;
+	/* Memory group identification. */
+	int mgid;
 
 	/*
 	 * We don't want to add too much memory if it's not getting onlined,
@@ -626,8 +628,8 @@ static int virtio_mem_add_memory(struct virtio_mem *vm,
uint64_t addr,
 		addr + size - 1);
 	/* Memory might get onlined immediately. */
 	atomic64_add(size, &vm->offline_size);
-	rc = add_memory_driver_managed(vm->nid, addr, size, vm->resource_name,
-				       MHP_MERGE_RESOURCE);
+	rc = add_memory_driver_managed(vm->mgid, addr, size, vm->resource_name,
+				       MHP_MERGE_RESOURCE | MHP_NID_IS_MGID);
 	if (rc) {
 		atomic64_sub(size, &vm->offline_size);
 		dev_warn(&vm->vdev->dev, "adding memory failed: %d\n",
rc);
@@ -2562,6 +2564,7 @@ static bool virtio_mem_has_memory_added(struct virtio_mem
*vm)
 static int virtio_mem_probe(struct virtio_device *vdev)
 {
 	struct virtio_mem *vm;
+	uint64_t unit_pages;
 	int rc;
 
 	BUILD_BUG_ON(sizeof(struct virtio_mem_req) != 24);
@@ -2596,6 +2599,16 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	if (rc)
 		goto out_del_vq;
 
+	/* use a single dynamic memory group to cover the whole memory device */
+	if (vm->in_sbm)
+		unit_pages = PHYS_PFN(memory_block_size_bytes());
+	else
+		unit_pages = PHYS_PFN(vm->bbm.bb_size);
+	rc = register_dynamic_memory_group(vm->nid, unit_pages);
+	if (rc < 0)
+		goto out_del_resource;
+	vm->mgid = rc;
+
 	/*
 	 * If we still have memory plugged, we have to unplug all memory first.
 	 * Registering our parent resource makes sure that this memory isn't
@@ -2610,7 +2623,7 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	vm->memory_notifier.notifier_call = virtio_mem_memory_notifier_cb;
 	rc = register_memory_notifier(&vm->memory_notifier);
 	if (rc)
-		goto out_del_resource;
+		goto out_unreg_group;
 	rc = register_virtio_mem_device(vm);
 	if (rc)
 		goto out_unreg_mem;
@@ -2624,6 +2637,8 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	return 0;
 out_unreg_mem:
 	unregister_memory_notifier(&vm->memory_notifier);
+out_unreg_group:
+	unregister_memory_group(vm->mgid);
 out_del_resource:
 	virtio_mem_delete_resource(vm);
 out_del_vq:
@@ -2688,6 +2703,7 @@ static void virtio_mem_remove(struct virtio_device *vdev)
 	} else {
 		virtio_mem_delete_resource(vm);
 		kfree_const(vm->resource_name);
+		unregister_memory_group(vm->mgid);
 	}
 
 	/* remove all tracking data - no locking needed */
-- 
2.31.1

Use memory groups to improve our "auto-movable" onlining policy:

1. For static memory groups (e.g., a DIMM), online a memory block MOVABLE
   only if all other memory blocks in the group are either MOVABLE or could
   be onlined MOVABLE. A DIMM will either be MOVABLE or not, not a mixture.

2. For dynamic memory groups (e.g., a virtio-mem device), online a
   memory block MOVABLE only if all other memory blocks inside the
   current unit are either MOVABLE or could be onlined MOVABLE. For a
   virtio-mem device with a device block size with 512 MiB, all 128 MiB
   memory blocks wihin a 512 MiB unit will either be MOVABLE or not, not
   a mixture.

We have to pass the memory group to zone_for_pfn_range() to take the
memory group into account.

Note: for now, there seems to be no compelling reason to make this
behavior configurable.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/base/memory.c          | 18 +++++++------
 include/linux/memory_hotplug.h |  3 ++-
 mm/memory_hotplug.c            | 48 +++++++++++++++++++++++++++++++---
 3 files changed, 57 insertions(+), 12 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index e96c4f436ac3..1d34f30a9a80 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -182,7 +182,8 @@ static int memory_block_online(struct memory_block *mem)
 	struct zone *zone;
 	int ret;
 
-	zone = zone_for_pfn_range(mem->online_type, mem->nid, start_pfn,
nr_pages);
+	zone = zone_for_pfn_range(mem->online_type, mem->nid, mem->group,
+				  start_pfn, nr_pages);
 
 	/*
 	 * Although vmemmap pages have a different lifecycle than the pages
@@ -379,12 +380,13 @@ static ssize_t phys_device_show(struct device *dev,
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
 static int print_allowed_zone(char *buf, int len, int nid,
+			      struct memory_group *group,
 			      unsigned long start_pfn, unsigned long nr_pages,
 			      int online_type, struct zone *default_zone)
 {
 	struct zone *zone;
 
-	zone = zone_for_pfn_range(online_type, nid, start_pfn, nr_pages);
+	zone = zone_for_pfn_range(online_type, nid, group, start_pfn, nr_pages);
 	if (zone == default_zone)
 		return 0;
 
@@ -397,9 +399,10 @@ static ssize_t valid_zones_show(struct device *dev,
 	struct memory_block *mem = to_memory_block(dev);
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
+	struct memory_group *group = mem->group;
 	struct zone *default_zone;
+	int nid = mem->nid;
 	int len = 0;
-	int nid;
 
 	/*
 	 * Check the existing zone. Make sure that we do that only on the
@@ -418,14 +421,13 @@ static ssize_t valid_zones_show(struct device *dev,
 		goto out;
 	}
 
-	nid = mem->nid;
-	default_zone = zone_for_pfn_range(MMOP_ONLINE, nid, start_pfn,
-					  nr_pages);
+	default_zone = zone_for_pfn_range(MMOP_ONLINE, nid, group,
+					  start_pfn, nr_pages);
 
 	len += sysfs_emit_at(buf, len, "%s", default_zone->name);
-	len += print_allowed_zone(buf, len, nid, start_pfn, nr_pages,
+	len += print_allowed_zone(buf, len, nid, group, start_pfn, nr_pages,
 				  MMOP_ONLINE_KERNEL, default_zone);
-	len += print_allowed_zone(buf, len, nid, start_pfn, nr_pages,
+	len += print_allowed_zone(buf, len, nid, group, start_pfn, nr_pages,
 				  MMOP_ONLINE_MOVABLE, default_zone);
 out:
 	len += sysfs_emit_at(buf, len, "\n");
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 23c4d369ad30..97f874a60607 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -348,7 +348,8 @@ extern void sparse_remove_section(struct mem_section *ms,
 extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
 					  unsigned long pnum);
 extern struct zone *zone_for_pfn_range(int online_type, int nid,
-		unsigned long start_pfn, unsigned long nr_pages);
+		struct memory_group *group, unsigned long start_pfn,
+		unsigned long nr_pages);
 extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
 				      struct mhp_params *params);
 void arch_remove_linear_mapping(u64 start, u64 size);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8d556396b5d4..93fb89efdc80 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -850,12 +850,53 @@ static struct zone *default_kernel_zone_for_pfn(int nid,
unsigned long start_pfn
  *    "present pages" is an upper limit that can get reached at
runtime. As
  *    we base our calculations on KERNEL_EARLY, this is not an issue.
  */
-static struct zone *auto_movable_zone_for_pfn(int nid, unsigned long pfn,
+static struct zone *auto_movable_zone_for_pfn(int nid,
+					      struct memory_group *group,
+					      unsigned long pfn,
 					      unsigned long nr_pages)
 {
+	unsigned long online_pages = 0, max_pages, end_pfn;
+	struct page *page;
+
 	if (!auto_movable_ratio)
 		goto kernel_zone;
 
+	if (group && !group->is_dynamic) {
+		max_pages = group->s.max_pages;
+		online_pages = group->present_movable_pages;
+
+		/* If anything is !MOVABLE online the rest !MOVABLE. */
+		if (group->present_kernel_pages)
+			goto kernel_zone;
+	} else if (!group || group->d.unit_pages == nr_pages) {
+		max_pages = nr_pages;
+	} else {
+		max_pages = group->d.unit_pages;
+		/*
+		 * Take a look at all online sections in the current unit.
+		 * We can safely assume that all pages within a section belong
+		 * to the same zone, because dynamic memory groups only deal
+		 * with hotplugged memory.
+		 */
+		pfn = ALIGN_DOWN(pfn, group->d.unit_pages);
+		end_pfn = pfn + group->d.unit_pages;
+		for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+			page = pfn_to_online_page(pfn);
+			if (!page)
+				continue;
+			/* If anything is !MOVABLE online the rest !MOVABLE. */
+			if (page_zonenum(page) != ZONE_MOVABLE)
+				goto kernel_zone;
+			online_pages += PAGES_PER_SECTION;
+		}
+	}
+
+	/*
+	 * Online MOVABLE if we could *currently* online all remaining parts
+	 * MOVABLE. We expect to (add+) online them immediately next, so if
+	 * nobody interferes, all will be MOVABLE if possible.
+	 */
+	nr_pages = max_pages - online_pages;
 	if (!auto_movable_can_online_movable(NUMA_NO_NODE, nr_pages))
 		goto kernel_zone;
 
@@ -895,7 +936,8 @@ static inline struct zone *default_zone_for_pfn(int nid,
unsigned long start_pfn
 }
 
 struct zone *zone_for_pfn_range(int online_type, int nid,
-		unsigned long start_pfn, unsigned long nr_pages)
+		struct memory_group *group, unsigned long start_pfn,
+		unsigned long nr_pages)
 {
 	if (online_type == MMOP_ONLINE_KERNEL)
 		return default_kernel_zone_for_pfn(nid, start_pfn, nr_pages);
@@ -904,7 +946,7 @@ struct zone *zone_for_pfn_range(int online_type, int nid,
 		return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
 
 	if (online_policy == ONLINE_POLICY_AUTO_MOVABLE)
-		return auto_movable_zone_for_pfn(nid, start_pfn, nr_pages);
+		return auto_movable_zone_for_pfn(nid, group, start_pfn, nr_pages);
 
 	return default_zone_for_pfn(nid, start_pfn, nr_pages);
 }
-- 
2.31.1

Currently, the "auto-movable" online policy does not allow for
hotplugged
KERNEL (ZONE_NORMAL) memory to increase the amount of MOVABLE memory we can
have, primarily, because there is no coordiantion across memory devices and
we don't want to create zone-imbalances accidentially when unplugging
memory.

However, within a single memory device it's different. Let's allow for
KERNEL memory within a dynamic memory group to allow for more MOVABLE
within the same memory group. The only thing we have to take care of is
that the managing driver avoids zone imbalances by unplugging MOVABLE
memory first, otherwise there can be corner cases where unplug of memory
could result in (accidential) zone imbalances.

virtio-mem is the only user of dynamic memory groups and recently added
support for prioritizing unplug of ZONE_MOVABLE over ZONE_NORMAL, so we
don't need a new toggle to enable it for dynamic memory groups.

We limit this handling to dynamic memory groups, because:

* We want to keep the runtime overhead for collecting stats when onlining
  a single memory block small. We tend to have only a handful of dynamic
  memory groups, but we can have quite some static memory groups (e.g., 256
  DIMMs).
* It doesn't make too much sense for static memory groups, as we try
  onlining all applicable memory blocks either completely to ZONE_MOVABLE
  or not. In ordinary operation, we won't have a mixture of zones
  within a static memory group.

When adding memory to a dynamic memory group, we'll first online memory to
ZONE_MOVABLE as long as early KERNEL memory allows for it. Then, we'll
online the next unit(s) to ZONE_NORMAL, until we can online the next
unit(s) to ZONE_MOVABLE.

For a simple virtio-mem device with a MOVABLE:KERNEL ratio of 3:1, it
will result in a layout like:

  [M][M][M][M][M][M][M][M][N][M][M][M][N][M][M][M]...
  ^ movable memory due to early kernel memory
			   ^ allows for more movable memory ...
			      ^-----^ ... here
				       ^ allows for more movable memory ...
				          ^-----^ ... here

While the created layout is sub-optimal when it comes to contiguous zones,
it gives us the maximum flexibility when dynamically growing/shrinking a
device; we can grow small VMs really big in small steps, and still
shrink reliably to e.g., 1/4 of the maximum VM size in this example,
removing full memory blocks along with meta data more reliably.

Mark dynamic memory groups in the xarray such that we can efficiently
iterate over them when collecting stats. In usual setups, we have one
virtio-mem device per NUMA node, and usually only a small number of NUMA
nodes.

Note: for now, there seems to be no compelling reason to make this
behavior configurable.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 drivers/base/memory.c  | 25 ++++++++++++++++++
 include/linux/memory.h |  3 +++
 mm/memory_hotplug.c    | 60 +++++++++++++++++++++++++++++++++++++++---
 3 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 1d34f30a9a80..e09084009f3b 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -86,6 +86,7 @@ static DEFINE_XARRAY(memory_blocks);
  * Memory groups, indexed by memory group identification (mgid).
  */
 static DEFINE_XARRAY_FLAGS(memory_groups, XA_FLAGS_ALLOC);
+#define MEMORY_GROUP_MARK_DYNAMIC	XA_MARK_1
 
 static BLOCKING_NOTIFIER_HEAD(memory_chain);
 
@@ -931,6 +932,8 @@ static int register_memory_group(struct memory_group group)
 		       GFP_KERNEL);
 	if (ret)
 		kfree(new_group);
+	else if (group.is_dynamic)
+		xa_set_mark(&memory_groups, mgid, MEMORY_GROUP_MARK_DYNAMIC);
 	return ret ? ret : mgid;
 }
 
@@ -987,3 +990,25 @@ struct memory_group *get_memory_group(int mgid)
 {
 	return xa_load(&memory_groups, mgid);
 }
+
+int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
+			       struct memory_group *excluded, void *arg)
+{
+	struct memory_group *group;
+	unsigned long index;
+	int ret = 0;
+
+	xa_for_each_marked(&memory_groups, index, group,
+			   MEMORY_GROUP_MARK_DYNAMIC) {
+		if (group == excluded)
+			continue;
+#ifdef CONFIG_NUMA
+		if (nid != NUMA_NO_NODE && group->nid != nid)
+			continue;
+#endif /* CONFIG_NUMA */
+		ret = func(group, arg);
+		if (ret)
+			break;
+	}
+	return ret;
+}
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 0eceb8467d9a..c56260853caf 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -142,6 +142,9 @@ extern int register_static_memory_group(int nid, unsigned
long max_pages);
 extern int register_dynamic_memory_group(int nid, unsigned long unit_pages);
 extern int unregister_memory_group(int mgid);
 struct memory_group *get_memory_group(int mgid);
+typedef int (*walk_memory_groups_func_t)(struct memory_group *, void *);
+int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
+			       struct memory_group *excluded, void *arg);
 
 #define CONFIG_MEM_BLOCK_SIZE	(PAGES_PER_SECTION<<PAGE_SHIFT)
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 93fb89efdc80..bfdaa28eb86f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -750,11 +750,44 @@ static void auto_movable_stats_account_zone(struct
auto_movable_stats *stats,
 		stats->kernel_early_pages -= zone->cma_pages;
 	}
 }
+struct auto_movable_group_stats {
+	unsigned long movable_pages;
+	unsigned long req_kernel_early_pages;
+};
 
-static bool auto_movable_can_online_movable(int nid, unsigned long nr_pages)
+static int auto_movable_stats_account_group(struct memory_group *group,
+					   void *arg)
+{
+	const int ratio = READ_ONCE(auto_movable_ratio);
+	struct auto_movable_group_stats *stats = arg;
+	long pages;
+
+	/*
+	 * We don't support modifying the config while the auto-movable online
+	 * mode is already enabled. Just avoid the division by zero below.
+	 */
+	if (!ratio)
+		return 0;
+
+	/*
+	 * Calculate how many early kernel pages this group requires to
+	 * satisfy the configured zone ratio.
+	 */
+	pages = group->present_movable_pages * 100 / ratio;
+	pages -= group->present_kernel_pages;
+
+	if (pages > 0)
+		stats->req_kernel_early_pages += pages;
+	stats->movable_pages += group->present_movable_pages;
+	return 0;
+}
+
+static bool auto_movable_can_online_movable(int nid, struct memory_group
*group,
+					    unsigned long nr_pages)
 {
-	struct auto_movable_stats stats = {};
 	unsigned long kernel_early_pages, movable_pages;
+	struct auto_movable_group_stats group_stats = {};
+	struct auto_movable_stats stats = {};
 	pg_data_t *pgdat = NODE_DATA(nid);
 	struct zone *zone;
 	int i;
@@ -775,6 +808,21 @@ static bool auto_movable_can_online_movable(int nid,
unsigned long nr_pages)
 	kernel_early_pages = stats.kernel_early_pages;
 	movable_pages = stats.movable_pages;
 
+	/*
+	 * Kernel memory inside dynamic memory group allows for more MOVABLE
+	 * memory within the same group. Remove the effect of all but the
+	 * current group from the stats.
+	 */
+	walk_dynamic_memory_groups(nid, auto_movable_stats_account_group,
+				   group, &group_stats);
+	if (kernel_early_pages <= group_stats.req_kernel_early_pages)
+		return false;
+	kernel_early_pages -= group_stats.req_kernel_early_pages;
+	movable_pages -= group_stats.movable_pages;
+
+	if (group && group->is_dynamic)
+		kernel_early_pages += group->present_kernel_pages;
+
 	/*
 	 * Test if we could online the given number of pages to ZONE_MOVABLE
 	 * and still stay in the configured ratio.
@@ -832,6 +880,10 @@ static struct zone *default_kernel_zone_for_pfn(int nid,
unsigned long start_pfn
  *    with unmovable allocations). While there are corner cases where it might
  *    still work, it is barely relevant in practice.
  *
+ * Exceptions are dynamic memory groups, which allow for more MOVABLE
+ * memory within the same memory group -- because in that case, there is
+ * coordination within the single memory device managed by a single driver.
+ *
  * We rely on "present pages" instead of "managed pages",
as the latter is
  * highly unreliable and dynamic in virtualized environments, and does not
  * consider boot time allocations. For example, memory ballooning adjusts the
@@ -897,12 +949,12 @@ static struct zone *auto_movable_zone_for_pfn(int nid,
 	 * nobody interferes, all will be MOVABLE if possible.
 	 */
 	nr_pages = max_pages - online_pages;
-	if (!auto_movable_can_online_movable(NUMA_NO_NODE, nr_pages))
+	if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
 		goto kernel_zone;
 
 #ifdef CONFIG_NUMA
 	if (auto_movable_numa_aware &&
-	    !auto_movable_can_online_movable(nid, nr_pages))
+	    !auto_movable_can_online_movable(nid, group, nr_pages))
 		goto kernel_zone;
 #endif /* CONFIG_NUMA */
 
-- 
2.31.1