From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: fix check_move_unevictable_pages() on THP
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.
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301405000.5954@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/vmscan.c~mm-fix-check_move_unevictable_pages-on-thp
+++ a/mm/vmscan.c
@@ -4268,8 +4268,14 @@ void check_move_unevictable_pages(struct
for (i = 0; i < pvec->nr; i++) {
struct page *page = pvec->pages[i];
struct pglist_data *pagepgdat = page_pgdat(page);
+ int nr_pages;
+
+ if (PageTransTail(page))
+ continue;
+
+ nr_pages = thp_nr_pages(page);
+ pgscanned += nr_pages;
- pgscanned++;
if (pagepgdat != pgdat) {
if (pgdat)
spin_unlock_irq(&pgdat->lru_lock);
@@ -4288,7 +4294,7 @@ void check_move_unevictable_pages(struct
ClearPageUnevictable(page);
del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
add_page_to_lru_list(page, lruvec, lru);
- pgrescued++;
+ pgrescued += nr_pages;
}
}
_
