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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, cai@lca.pw, hannes@cmpxchg.org,
	hughd@google.com, linux-mm@kvack.org, mhocko@suse.com,
	mike.kravetz@oracle.com, mm-commits@vger.kernel.org,
	shakeelb@google.com, shy828301@gmail.com,
	torvalds@linux-foundation.org
Subject: [patch 05/15] mm: fix check_move_unevictable_pages() on THP
Date: Fri, 18 Sep 2020 21:20:12 -0700
Message-ID: <20200919042012.n9ppaodpA%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200918211925.7e97f0ef63d92f5cfe5ccbc5@linux-foundation.org>

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(-)

--- 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;
 		}
 	}
 
_

  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-19  4:19 incoming Andrew Morton
2020-09-19  4:20 ` [patch 01/15] mailmap: add older email addresses for Kees Cook Andrew Morton
2020-09-19  4:20 ` [patch 02/15] ksm: reinstate memcg charge on copied pages Andrew Morton
2020-09-19  4:20 ` [patch 03/15] mm: migration of hugetlbfs page skip memcg Andrew Morton
2020-09-19  4:20 ` [patch 04/15] shmem: shmem_writepage() split unlikely i915 THP Andrew Morton
2020-09-19  4:20 ` Andrew Morton [this message]
2020-09-19  4:20 ` [patch 06/15] mlock: fix unevictable_pgs event counts on THP Andrew Morton
2020-09-19  4:20 ` [patch 07/15] tmpfs: restore functionality of nr_inodes=0 Andrew Morton
2020-09-19  4:20 ` [patch 08/15] kprobes: fix kill kprobe which has been marked as gone Andrew Morton
2020-09-19  4:20 ` [patch 09/15] mm/thp: fix __split_huge_pmd_locked() for migration PMD Andrew Morton
2020-09-19  4:20 ` [patch 10/15] selftests/vm: fix display of page size in map_hugetlb Andrew Morton
2020-09-19  4:20 ` [patch 11/15] mm/memory_hotplug: drain per-cpu pages again during memory offline Andrew Morton
2020-09-19  4:20 ` [patch 12/15] ftrace: let ftrace_enable_sysctl take a kernel pointer buffer Andrew Morton
2020-09-19  4:20 ` [patch 13/15] stackleak: let stack_erasing_sysctl " Andrew Morton
2020-09-19  4:20 ` [patch 14/15] fs/fs-writeback.c: adjust dirtytime_interval_handler definition to match prototype Andrew Morton
2020-09-19  4:20 ` [patch 15/15] kcsan: kconfig: move to menu 'Generic Kernel Debugging Instruments' Andrew Morton

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