From d2e5fb927ee7f52c1fe2a98b554881e9dffd8514 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Fri, 30 Aug 2019 16:04:50 -0700 Subject: [PATCH] mm, memcg: do not set reclaim_state on soft limit reclaim Adric Blake has noticed[1] the following warning: WARNING: CPU: 7 PID: 175 at mm/vmscan.c:245 set_task_reclaim_state+0x1e/0x40 [...] Call Trace: mem_cgroup_shrink_node+0x9b/0x1d0 mem_cgroup_soft_limit_reclaim+0x10c/0x3a0 balance_pgdat+0x276/0x540 kswapd+0x200/0x3f0 ? wait_woken+0x80/0x80 kthread+0xfd/0x130 ? balance_pgdat+0x540/0x540 ? kthread_park+0x80/0x80 ret_from_fork+0x35/0x40 ---[ end trace 727343df67b2398a ]--- which tells us that soft limit reclaim is about to overwrite the reclaim_state configured up in the call chain (kswapd in this case but the direct reclaim is equally possible). This means that reclaim stats would get misleading once the soft reclaim returns and another reclaim is done. Fix the warning by dropping set_task_reclaim_state from the soft reclaim which is always called with reclaim_state set up. [1] http://lkml.kernel.org/r/CAE1jjeePxYPvw1mw2B3v803xHVR_BNnz0hQUY_JDMN8ny29M6w@mail.gmail.com Link: http://lkml.kernel.org/r/20190828071808.20410-1-mhocko@kernel.org Signed-off-by: Michal Hocko Reported-by: Adric Blake Acked-by: Yafang Shao Acked-by: Yang Shi Cc: Johannes Weiner Cc: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index c77d1e3761a7..a6c5d0b28321 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3220,6 +3220,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, #ifdef CONFIG_MEMCG +/* Only used by soft limit reclaim. Do not reuse for anything else. */ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, gfp_t gfp_mask, bool noswap, pg_data_t *pgdat, @@ -3235,7 +3236,8 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, }; unsigned long lru_pages; - set_task_reclaim_state(current, &sc.reclaim_state); + WARN_ON_ONCE(!current->reclaim_state); + sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); @@ -3253,7 +3255,6 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); - set_task_reclaim_state(current, NULL); *nr_scanned = sc.nr_scanned; return sc.nr_reclaimed;