Ocfs2 devel - Apr 2010 - Cleancache [PATCH 2/7] (was Transcendent Memory): core files

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Cleancache [PATCH 2/7] (was Transcendent Memory): core files

Cleancache core files.

Credits: Cleancache_ops design derived from Jeremy Fitzhardinge
design for tmem; sysfs code modelled after mm/ksm.c

Note that CONFIG_CLEANCACHE defaults to on; all hooks devolve
to a compare-pointer-to-NULL so performance impact should
be negligible, but can be reduced to zero impact if config''ed off.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>

Diffstat:
 include/linux/cleancache.h               |   88 +++++++++
 mm/Kconfig                               |   22 ++
 mm/Makefile                              |    1 
 mm/cleancache.c                          |  198 +++++++++++++++++++++
 4 files changed, 309 insertions(+)

--- linux-2.6.34-rc5/include/linux/cleancache.h	1969-12-31 17:00:00.000000000
-0700
+++ linux-2.6.34-rc5-cleancache/include/linux/cleancache.h	2010-04-21
10:06:33.000000000 -0600
@@ -0,0 +1,88 @@
+#ifndef _LINUX_CLEANCACHE_H
+#define _LINUX_CLEANCACHE_H
+
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+struct cleancache_ops {
+	int (*init_fs)(unsigned long);
+	int (*init_shared_fs)(char *uuid, unsigned long);
+	int (*get_page)(int, unsigned long, unsigned long, struct page *);
+	int (*put_page)(int, unsigned long, unsigned long, struct page *);
+	int (*flush_page)(int, unsigned long, unsigned long);
+	int (*flush_inode)(int, unsigned long);
+	void (*flush_fs)(int);
+};
+
+extern struct cleancache_ops *cleancache_ops;
+extern int __cleancache_get_page(struct page *);
+extern int __cleancache_put_page(struct page *);
+extern int __cleancache_flush_page(struct address_space *, struct page *);
+extern int __cleancache_flush_inode(struct address_space *);
+
+#ifndef CONFIG_CLEANCACHE
+#define cleancache_ops ((struct cleancache_ops *)NULL)
+#endif
+
+static inline int cleancache_init_fs(unsigned long pagesize)
+{
+	int ret = -1;
+
+	if (cleancache_ops)
+		ret = (*cleancache_ops->init_fs)(pagesize);
+	return ret;
+}
+
+static inline int cleancache_init_shared_fs(char *uuid, unsigned long pagesize)
+{
+	int ret = -1;
+
+	if (cleancache_ops)
+		ret = (*cleancache_ops->init_shared_fs)(uuid, pagesize);
+	return ret;
+}
+
+static inline int cleancache_get_page(struct page *page)
+{
+	int ret = 0;
+
+	if (cleancache_ops)
+		ret = __cleancache_get_page(page);
+	return ret;
+}
+
+static inline int cleancache_put_page(struct page *page)
+{
+	int ret = 0;
+
+	if (cleancache_ops)
+		ret = __cleancache_put_page(page);
+	return ret;
+}
+
+static inline int cleancache_flush_page(struct address_space *mapping,
+					struct page *page)
+{
+	int ret = 0;
+
+	if (cleancache_ops)
+		ret = __cleancache_flush_page(mapping, page);
+	return ret;
+}
+
+static inline int cleancache_flush_inode(struct address_space *mapping)
+{
+	int ret = 0;
+
+	if (cleancache_ops)
+		ret = __cleancache_flush_inode(mapping);
+	return ret;
+}
+
+static inline void cleancache_flush_fs(int pool_id)
+{
+	if (cleancache_ops && pool_id >= 0)
+		(*cleancache_ops->flush_fs)(pool_id);
+}
+
+#endif /* _LINUX_CLEANCACHE_H */
--- linux-2.6.34-rc5/mm/cleancache.c	1969-12-31 17:00:00.000000000 -0700
+++ linux-2.6.34-rc5-cleancache/mm/cleancache.c	2010-04-21 10:06:33.000000000
-0600
@@ -0,0 +1,198 @@
+/* mm/cleancache.c
+
+ Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
+ Author: Dan Magenheimer
+
+ Cleancache can be thought of as a page-granularity victim cache for clean
+ pages that the kernel''s pageframe replacement algorithm (PFRA) would
like
+ to keep around, but can''t since there isn''t enough memory. 
So when the
+ PFRA "evicts" a page, it first attempts to put it into a synchronous
+ concurrency-safe page-oriented pseudo-RAM device (such as Xen''s
Transcendent
+ Memory, aka "tmem", or in-kernel compressed memory, aka
"zmem", or other
+ RAM-like devices) which is not directly accessible or addressable by the
+ kernel and is of unknown and possibly time-varying size.  And when a
+ cleancache-enabled filesystem wishes to access a page in a file on disk,
+ it first checks cleancache to see if it already contains it; if it does,
+ the page is copied into the kernel and a disk access is avoided.
+ This pseudo-RAM device links itself to cleancache by setting the
+ cleancache_ops pointer appropriately and the functions it provides must
+ conform to certain semantics as follows:
+
+ Most important, cleancache is "ephemeral".  Pages which are copied
into
+ cleancache have an indefinite lifetime which is completely unknowable
+ by the kernel and so may or may not still be in cleancache at any later time.
+ Thus, as its name implies, cleancache is not suitable for dirty pages.  The
+ pseudo-RAM has complete discretion over what pages to preserve and what
+ pages to discard and when.
+
+ A filesystem calls "init_fs" to obtain a pool id which, if positive,
must be
+ saved in the filesystem''s superblock; a negative return value
indicates
+ failure.  A "put_page" will copy a (presumably about-to-be-evicted)
page into
+ pseudo-RAM and associate it with the pool id, the file inode, and a page
+ index into the file.  (The combination of a pool id, an inode, and an index
+ is called a "handle".)  A "get_page" will copy the page,
if found, from
+ pseudo-RAM into kernel memory.  A "flush_page" will ensure the page
no longer
+ is present in pseudo-RAM; a "flush_inode" will flush all pages
associated
+ with the specified inode; and a "flush_fs" will flush all pages in
all
+ inodes specified by the given pool id.
+
+ A "init_shared_fs", like init, obtains a pool id but tells the
pseudo-RAM
+ to treat the pool as shared using a 128-bit UUID as a key.  On systems
+ that may run multiple kernels (such as hard partitioned or virtualized
+ systems) that may share a clustered filesystem, and where the pseudo-RAM
+ may be shared among those kernels, calls to init_shared_fs that specify the
+ same UUID will receive the same pool id, thus allowing the pages to
+ be shared.  Note that any security requirements must be imposed outside
+ of the kernel (e.g. by "tools" that control the pseudo-RAM).  Or a
+ pseudo-RAM implementation can simply disable shared_init by always
+ returning a negative value.
+
+ If a get_page is successful on a non-shared pool, the page is flushed (thus
+ making cleancache an "exclusive" cache).  On a shared pool, the page
+ is NOT flushed on a successful get_page so that it remains accessible to
+ other sharers.  The kernel is responsible for ensuring coherency between
+ cleancache (shared or not), the page cache, and the filesystem, using
+ cleancache flush operations as required.
+
+ Note that the pseudo-RAM must enforce put-put-get coherency and get-get
+ coherency.  For the former, if two puts are made to the same handle but
+ with different data, say AAA by the first put and BBB by the second, a
+ subsequent get can never return the stale data (AAA).  For get-get coherency,
+ if a get for a given handle fails, subsequent gets for that handle will
+ never succeed unless preceded by a successful put with that handle.
+
+ Last, pseudo-RAM provides no SMP serialization guarantees; if two
+ different Linux threads are putting an flushing a page with the same
+ handle, the results are indeterminate.
+
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/cleancache.h>
+
+struct cleancache_ops *cleancache_ops;
+EXPORT_SYMBOL(cleancache_ops);
+
+/* useful stats available via /sys/kernel/mm/frontswap */
+static unsigned long succ_gets;
+static unsigned long failed_gets;
+static unsigned long puts;
+static unsigned long flushes;
+
+int __cleancache_get_page(struct page *page)
+{
+	int ret = 0;
+	int pool_id = page->mapping->host->i_sb->cleancache_poolid;
+
+	if (pool_id >= 0) {
+		ret = (*cleancache_ops->get_page)(pool_id,
+				page->mapping->host->i_ino, page->index, page);
+		if (ret == 1)
+			succ_gets++;
+		else
+			failed_gets++;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(__cleancache_get_page);
+
+int __cleancache_put_page(struct page *page)
+{
+	int ret = 0;
+	int pool_id = page->mapping->host->i_sb->cleancache_poolid;
+
+	if (pool_id >= 0) {
+		ret = (*cleancache_ops->put_page)(pool_id,
+				page->mapping->host->i_ino, page->index, page);
+		puts++;
+	}
+	return ret;
+}
+
+int __cleancache_flush_page(struct address_space *mapping, struct page *page)
+{
+	int ret = 0;
+	int pool_id = mapping->host->i_sb->cleancache_poolid;
+
+	if (pool_id >= 0) {
+		ret = (*cleancache_ops->flush_page)(pool_id,
+				mapping->host->i_ino, page->index);
+		flushes++;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(__cleancache_flush_page);
+
+int __cleancache_flush_inode(struct address_space *mapping)
+{
+	int ret = 0;
+	int pool_id = mapping->host->i_sb->cleancache_poolid;
+
+	if (pool_id >= 0) {
+		ret = (*cleancache_ops->flush_inode)(pool_id,
+						     mapping->host->i_ino);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(__cleancache_flush_inode);
+
+#ifdef CONFIG_SYSFS
+
+#define CLEANCACHE_ATTR_RO(_name) \
+	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+
+static ssize_t succ_gets_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", succ_gets);
+}
+CLEANCACHE_ATTR_RO(succ_gets);
+
+static ssize_t failed_gets_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", failed_gets);
+}
+CLEANCACHE_ATTR_RO(failed_gets);
+
+static ssize_t puts_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", puts);
+}
+CLEANCACHE_ATTR_RO(puts);
+
+static ssize_t flushes_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", flushes);
+}
+CLEANCACHE_ATTR_RO(flushes);
+
+static struct attribute *cleancache_attrs[] = {
+	&succ_gets_attr.attr,
+	&failed_gets_attr.attr,
+	&puts_attr.attr,
+	&flushes_attr.attr,
+	NULL,
+};
+
+static struct attribute_group cleancache_attr_group = {
+	.attrs = cleancache_attrs,
+	.name = "cleancache",
+};
+
+#endif /* CONFIG_SYSFS */
+
+static int __init init_cleancache(void)
+{
+#ifdef CONFIG_SYSFS
+	int err;
+
+	err = sysfs_create_group(mm_kobj, &cleancache_attr_group);
+#endif /* CONFIG_SYSFS */
+	return 0;
+}
+module_init(init_cleancache)
--- linux-2.6.34-rc5/mm/Kconfig	2010-04-19 17:29:56.000000000 -0600
+++ linux-2.6.34-rc5-cleancache/mm/Kconfig	2010-04-21 10:06:33.000000000 -0600
@@ -287,3 +287,25 @@ config NOMMU_INITIAL_TRIM_EXCESS
 	  of 1 says that all excess pages should be trimmed.
 
 	  See Documentation/nommu-mmap.txt for more information.
+
+config CLEANCACHE
+	bool "Enable cleancache pseudo-RAM driver to cache clean pages"
+	default y
+	help
+ 	  Cleancache can be thought of as a page-granularity victim cache
+	  for clean pages that the kernel''s pageframe replacement algorithm
+	  (PFRA) would like to keep around, but can''t since there
isn''t enough
+	  memory.  So when the PFRA "evicts" a page, it first attempts to
put
+	  it into a synchronous concurrency-safe page-oriented pseudo-RAM
+	  device (such as Xen''s Transcendent Memory, aka "tmem")
which is not
+	  directly accessible or addressable by the kernel and is of unknown
+	  (and possibly time-varying) size.  And when a cleancache-enabled
+	  filesystem wishes to access a page in a file on disk, it first
+	  checks cleancache to see if it already contains it; if it does,
+ 	  the page is copied into the kernel and a disk access is avoided.
+	  When a pseudo-RAM device is available, a significant I/O reduction
+	  may be achieved.  When none is available, all cleancache calls
+	  are reduced to a single pointer-compare-against-NULL resulting
+	  in a negligible performance hit.
+
+	  If unsure, say Y to enable cleancache
--- linux-2.6.34-rc5/mm/Makefile	2010-04-19 17:29:56.000000000 -0600
+++ linux-2.6.34-rc5-cleancache/mm/Makefile	2010-04-21 10:06:33.000000000 -0600
@@ -44,3 +44,4 @@ obj-$(CONFIG_MEMORY_FAILURE) += memory-f
 obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
+obj-$(CONFIG_CLEANCACHE) += cleancache.o
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On Thu, Apr 22, 2010 at 06:28:09AM -0700, Dan Magenheimer
wrote:
> +struct cleancache_ops {
> +	int (*init_fs)(unsigned long);
unsigned long?  Really?  Not even size_t?
> +	int (*init_shared_fs)(char *uuid, unsigned long);
Ditto.
> +	int (*get_page)(int, unsigned long, unsigned long, struct page *);
Ugh.  First of all, presumably you have some structure behind that index,
don't you?  Might be a better way to do it.

What's more, use of ->i_ino is simply wrong.  How stable do you want that
to be and how much do you want it to outlive struct address_space in
question?
>From my reading of your code, it doesn't outlive that anyway, so...
The third one is pgoff_t; again, use sane types, _if_ you actually want
the argument #3 at all - it can be derived from struct page you are passing
there as well.
> +	int (*put_page)(int, unsigned long, unsigned long, struct page *);
> +	int (*flush_page)(int, unsigned long, unsigned long);
> +	int (*flush_inode)(int, unsigned long);
> +	void (*flush_fs)(int);
Same questions as above...

> From: Al Viro [mailto:viro at ZenIV.linux.org.uk]
> Subject: Re: Cleancache [PATCH 2/7] (was Transcendent Memory): core files
Hi Al!

Thanks for the feedback!  Sorry for the delayed response.
> ...again, use sane types...
Good point.  Will fix types for next rev (using size_t, ino_t,
and pgoff_t).
> > +	int (*get_page)(int, unsigned long, unsigned long, struct page *);
> 
> Ugh.  First of all, presumably you have some structure behind that
> index, don't you?  Might be a better way to do it.
Not quite sure what you mean here.  The index is really
just part of a unique handle for cleancache to identify
the (page of) data.
> What's more, use of ->i_ino is simply wrong.  How stable do you want
that
> to be and how much do you want it to outlive struct address_space in
question?
> From my reading of your code, it doesn't outlive that anyway, so...
Unless I misunderstand your point, no, the inode never outlives
the address space because the specification requires the kernel
to ensure coherency; if the inode were about to outlive the
address space, the cleancache_flush operations must be invoked
(and I think the patch covers all the necessary cases).
> The third one is pgoff_t; again, use sane types, _if_ you actually want
> the argument #3 at all - it can be derived from struct page you are
> passing there as well.
I thought it best to declare the _ops so that the struct page
is opaque to the "backend" (driver).  The kernel-side
("frontend")
defines the handle and ensures coherency, so the backend shouldn't
be allowed to derive or muck with the three-tuple passed by the
kernel. In the existing (Xen tmem) driver, the only operation
performed on the struct page parameter is page_to_pfn().  OTOH,
I could go one step further and pass a pfn_t instead of a
struct page, since it is really only the physical page frame that
the backend needs to know about and (synchronously) read/write from/to.

Thoughts?

Thanks again!
Dan

> > The third one is pgoff_t; again, use sane types, _if_ you actually
> want
> > the argument #3 at all - it can be derived from struct page you are
> > passing there as well.
> 
> I thought it best to declare the _ops so that the struct page
> is opaque to the "backend" (driver).  The kernel-side
("frontend")
> defines the handle and ensures coherency, so the backend shouldn't
> be allowed to derive or muck with the three-tuple passed by the
> kernel. In the existing (Xen tmem) driver, the only operation
> performed on the struct page parameter is page_to_pfn().  OTOH,
> I could go one step further and pass a pfn_t instead of a
> struct page, since it is really only the physical page frame that
> the backend needs to know about and (synchronously) read/write from/to.
> 
> Thoughts?
Silly me.  pfn_t is a Xen/KVM type not otherwise used in the
kernel AFAICT.  Please ignore...