From b7ff0f629df76aac132ea408349b97f5d4d93a4e Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Tue, 4 Apr 2023 00:13:51 +0000 Subject: [PATCH] mm: vmscan: move set_task_reclaim_state() after global_reclaim() Patch series "Ignore non-LRU-based reclaim in memcg reclaim", v4. Upon running some proactive reclaim tests using memory.reclaim, we noticed some tests flaking where writing to memory.reclaim would be successful even though we did not reclaim the requested amount fully. Looking further into it, I discovered that *sometimes* we over-report the number of reclaimed pages in memcg reclaim. Reclaimed pages through other means than LRU-based reclaim are tracked through reclaim_state in struct scan_control, which is stashed in current task_struct. These pages are added to the number of reclaimed pages through LRUs. For memcg reclaim, these pages generally cannot be linked to the memcg under reclaim and can cause an overestimated count of reclaimed pages. This short series tries to address that. Patches 1-2 are just refactoring, they add helpers that wrap some operations on current->reclaim_state, and rename reclaim_state->reclaimed_slab to reclaim_state->reclaimed. Patch 3 ignores pages reclaimed outside of LRU reclaim in memcg reclaim. The pages are uncharged anyway, so even if we end up under-reporting reclaimed pages we will still succeed in making progress during charging. Do not be fooled by the diffstat - the core of this series is patch 3, which has one line of code change. All the rest is refactoring and one huge comment. This patch (of 3): set_task_reclaim_state() is currently defined in mm/vmscan.c above an #ifdef CONFIG_MEMCG block where global_reclaim() is defined. We are about to add some more helpers that operate on reclaim_state, and will need to use global_reclaim(). Move set_task_reclaim_state() after the #ifdef CONFIG_MEMCG block containing the definition of global_reclaim() to keep helpers operating on reclaim_state together. Link: https://lkml.kernel.org/r/20230404001353.468224-1-yosryahmed@google.com Link: https://lkml.kernel.org/r/20230404001353.468224-2-yosryahmed@google.com Signed-off-by: Yosry Ahmed Cc: Christoph Lameter Cc: Darrick J. Wong Cc: Dave Chinner Cc: David Hildenbrand Cc: David Rientjes Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Johannes Weiner Cc: Joonsoo Kim Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Michal Hocko Cc: NeilBrown Cc: Peter Xu Cc: Roman Gushchin Cc: Shakeel Butt Cc: Vlastimil Babka Cc: Yu Zhao Signed-off-by: Andrew Morton --- mm/vmscan.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index ebbc2265871d..83388b22fce9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -189,18 +189,6 @@ struct scan_control { */ int vm_swappiness = 60; -static void set_task_reclaim_state(struct task_struct *task, - struct reclaim_state *rs) -{ - /* Check for an overwrite */ - WARN_ON_ONCE(rs && task->reclaim_state); - - /* Check for the nulling of an already-nulled member */ - WARN_ON_ONCE(!rs && !task->reclaim_state); - - task->reclaim_state = rs; -} - LIST_HEAD(shrinker_list); DEFINE_MUTEX(shrinker_mutex); DEFINE_SRCU(shrinker_srcu); @@ -528,6 +516,18 @@ static bool writeback_throttling_sane(struct scan_control *sc) } #endif +static void set_task_reclaim_state(struct task_struct *task, + struct reclaim_state *rs) +{ + /* Check for an overwrite */ + WARN_ON_ONCE(rs && task->reclaim_state); + + /* Check for the nulling of an already-nulled member */ + WARN_ON_ONCE(!rs && !task->reclaim_state); + + task->reclaim_state = rs; +} + static long xchg_nr_deferred(struct shrinker *shrinker, struct shrink_control *sc) { -- 2.50.1