diff mbox series

[05/15] mm: fix check_move_unevictable_pages() on THP

Message ID 20200919042012.n9ppaodpA%akpm@linux-foundation.org
State New
Headers show
Series [01/15] mailmap: add older email addresses for Kees Cook | expand

Commit Message

Andrew Morton Sept. 19, 2020, 4:20 a.m. UTC
From: Hugh Dickins <hughd@google.com>
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@google.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 mm/vmscan.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
diff mbox series


--- 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)
@@ -4288,7 +4294,7 @@  void check_move_unevictable_pages(struct
 			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
 			add_page_to_lru_list(page, lruvec, lru);
-			pgrescued++;
+			pgrescued += nr_pages;