David Hildenbrand
2021-Aug-09 07:35 UTC
[RFC PATCH 09/15] virtio: virtio_mem: use PAGES_PER_SECTION instead of MAX_ORDER_NR_PAGES
On 05.08.21 21:02, Zi Yan wrote:> From: Zi Yan <ziy at nvidia.com> > > It keeps the existing behavior when MAX_ORDER grows beyond a section > size. > > Signed-off-by: Zi Yan <ziy at nvidia.com> > Cc: David Hildenbrand <david at redhat.com> > Cc: "Michael S. Tsirkin" <mst at redhat.com> > Cc: Jason Wang <jasowang at redhat.com> > Cc: virtualization at lists.linux-foundation.org > Cc: linux-mm at kvack.org > Cc: linux-kernel at vger.kernel.org > --- > drivers/virtio/virtio_mem.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c > index 19036922f7ef..bab5a81fa796 100644 > --- a/drivers/virtio/virtio_mem.c > +++ b/drivers/virtio/virtio_mem.c > @@ -1105,11 +1105,11 @@ static void virtio_mem_clear_fake_offline(unsigned long pfn, > */ > static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages) > { > - const unsigned long max_nr_pages = MAX_ORDER_NR_PAGES; > + const unsigned long max_nr_pages = PAGES_PER_SECTION; > unsigned long i; > > /* > - * We are always called at least with MAX_ORDER_NR_PAGES > + * We are always called at least with PAGES_PER_SECTION > * granularity/alignment (e.g., the way subblocks work). All pages > * inside such a block are alike. > */ > @@ -1125,7 +1125,7 @@ static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages) > if (PageDirty(page)) { > virtio_mem_clear_fake_offline(pfn + i, max_nr_pages, > false); > - generic_online_page(page, MAX_ORDER - 1); > + generic_online_page(page, PAGES_PER_SECTION - 1); > } else { > virtio_mem_clear_fake_offline(pfn + i, max_nr_pages, > true); > @@ -1228,7 +1228,7 @@ static void virtio_mem_online_page_cb(struct page *page, unsigned int order) > if (vm->in_sbm) { > /* > * We exploit here that subblocks have at least > - * MAX_ORDER_NR_PAGES size/alignment - so we cannot > + * PAGES_PER_SECTION size/alignment - so we cannot > * cross subblocks within one call. > */ > id = virtio_mem_phys_to_mb_id(addr); > @@ -2438,14 +2438,14 @@ static int virtio_mem_init(struct virtio_mem *vm) > VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD); > > /* > - * We want subblocks to span at least MAX_ORDER_NR_PAGES and > + * We want subblocks to span at least PAGES_PER_SECTION and > * pageblock_nr_pages pages. This: > * - Simplifies our page onlining code (virtio_mem_online_page_cb) > * and fake page onlining code (virtio_mem_fake_online). > * - Is required for now for alloc_contig_range() to work reliably - > * it doesn't properly handle smaller granularity on ZONE_NORMAL. > */ > - sb_size = max_t(uint64_t, MAX_ORDER_NR_PAGES, > + sb_size = max_t(uint64_t, PAGES_PER_SECTION, > pageblock_nr_pages) * PAGE_SIZE; > sb_size = max_t(uint64_t, vm->device_block_size, sb_size); > >This is very much completely broken and destroys most of the purpose of virtio-mem. It even is broken once MAX_ORDER would exceed a single memory section I think. Whatever you do, keep virtio-mem working *as is* unless someone explicitly sets MAX_ORDER on the command line to something bigger. virtio-mem will require some minor adjustments once MAX_ORDER_NR_PAGES would exceed the memory section size -- the functionality will, however, be heavily degraded once you increase MAX_ORDER_NR_PAGES in any way (again, which is fine if it's explicitly done by an admin on the command line). As mentioned somewhere else already, we'll have to tackle alloc_contig_range() to properly deal with pageblock_order granularity, then we can rework virtio-mem code to be based on that instead of MAX_ORDER - 1. -- Thanks, David / dhildenb