From: Hugh Dickins hughd@google.com
mainline inclusion from mainline-v5.9-rc6 commit 8d8869ca5d2d9d86db96271ab063fdcfa9baf5b4 category: bugfix bugzilla: 36232 CVE: NA
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check_move_unevictable_pages() is used in making unevictable shmem pages evictable: by shmem_unlock_mapping(), drm_gem_check_release_pagevec() and i915/gem check_release_pagevec(). Those may pass down subpages of a huge page, when /sys/kernel/mm/transparent_hugepage/shmem_enabled is "force".
That does not crash or warn at present, but the accounting of vmstats unevictable_pgs_scanned and unevictable_pgs_rescued is inconsistent: scanned being incremented on each subpage, rescued only on the head (since tails already appear evictable once the head has been updated).
5.8 commit 5d91f31faf8e ("mm: swap: fix vmstats for huge page") has established that vm_events in general (and unevictable_pgs_rescued in particular) should count every subpage: so follow that precedent here.
Do this in such a way that if mem_cgroup_page_lruvec() is made stricter (to check page->mem_cgroup is always set), no problem: skip the tails before calling it, and add thp_nr_pages() to vmstats on the head.
Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Shakeel Butt shakeelb@google.com Acked-by: Yang Shi shy828301@gmail.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@suse.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Qian Cai cai@lca.pw Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301405000.5954@eggly.anvils Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- mm/vmscan.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 92f2489efda8..4a0fd5d6c4a2 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4366,8 +4366,14 @@ void check_move_unevictable_pages(struct page **pages, int nr_pages) for (i = 0; i < nr_pages; i++) { struct page *page = pages[i]; struct pglist_data *pagepgdat = page_pgdat(page); + int _nr_pages; + + if (PageTransTail(page)) + continue; + + _nr_pages = hpage_nr_pages(page); + pgscanned += _nr_pages;
- pgscanned++; if (pagepgdat != pgdat) { if (pgdat) spin_unlock_irq(&pgdat->lru_lock); @@ -4386,7 +4392,7 @@ void check_move_unevictable_pages(struct page **pages, int nr_pages) ClearPageUnevictable(page); del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); add_page_to_lru_list(page, lruvec, lru); - pgrescued++; + pgrescued += _nr_pages; } }