From: Yosry Ahmed yosryahmed@google.com
[ Upstream commit b006847222623ac3cda8589d15379eac86a2bcb7 ]
The workingset code flushes the stats in workingset_refault() to get accurate stats of the eviction memcg. In preparation for more scoped flushed and passing the eviction memcg to the flush call, move the call to workingset_test_recent() where we have a pointer to the eviction memcg.
The flush call is sleepable, and cannot be made in an rcu read section. Hence, minimize the rcu read section by also moving it into workingset_test_recent(). Furthermore, instead of holding the rcu read lock throughout workingset_test_recent(), only hold it briefly to get a ref on the eviction memcg. This allows us to make the flush call after we get the eviction memcg.
As for workingset_refault(), nothing else there appears to be protected by rcu. The memcg of the faulted folio (which is not necessarily the same as the eviction memcg) is protected by the folio lock, which is held from all callsites. Add a VM_BUG_ON() to make sure this doesn't change from under us.
No functional change intended.
Link: https://lkml.kernel.org/r/20231129032154.3710765-5-yosryahmed@google.com Signed-off-by: Yosry Ahmed yosryahmed@google.com Tested-by: Domenico Cerasuolo cerasuolodomenico@gmail.com Acked-by: Shakeel Butt shakeelb@google.com Cc: Chris Li chrisl@kernel.org Cc: Greg Thelen gthelen@google.com Cc: Ivan Babrou ivan@cloudflare.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Michal Koutny mkoutny@suse.com Cc: Muchun Song muchun.song@linux.dev Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Tejun Heo tj@kernel.org Cc: Waiman Long longman@redhat.com Cc: Wei Xu weixugc@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Leon Huang Fu leon.huangfu@shopee.com --- mm/workingset.c | 36 ++++++++++++++++++++++++------------ 1 file changed, 24 insertions(+), 12 deletions(-)
diff --git a/mm/workingset.c b/mm/workingset.c index 9110957bec5b..6e61ad08df75 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -425,8 +425,16 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset) struct pglist_data *pgdat; unsigned long eviction;
- if (lru_gen_enabled()) - return lru_gen_test_recent(shadow, file, &eviction_lruvec, &eviction, workingset); + rcu_read_lock(); + + if (lru_gen_enabled()) { + bool recent = lru_gen_test_recent(shadow, file, + &eviction_lruvec, &eviction, workingset); + + rcu_read_unlock(); + return recent; + } +
unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset); eviction <<= bucket_order; @@ -448,8 +456,16 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset) * configurations instead. */ eviction_memcg = mem_cgroup_from_id(memcgid); - if (!mem_cgroup_disabled() && !eviction_memcg) + if (!mem_cgroup_disabled() && + (!eviction_memcg || !mem_cgroup_tryget(eviction_memcg))) { + rcu_read_unlock(); return false; + } + + rcu_read_unlock(); + + /* Flush stats (and potentially sleep) outside the RCU read section */ + mem_cgroup_flush_stats_ratelimited();
eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat); refault = atomic_long_read(&eviction_lruvec->nonresident_age); @@ -493,6 +509,7 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset) } }
+ mem_cgroup_put(eviction_memcg); return refault_distance <= workingset_size; }
@@ -519,19 +536,16 @@ void workingset_refault(struct folio *folio, void *shadow) return; }
- /* Flush stats (and potentially sleep) before holding RCU read lock */ - mem_cgroup_flush_stats_ratelimited(); - - rcu_read_lock(); - /* * The activation decision for this folio is made at the level * where the eviction occurred, as that is where the LRU order * during folio reclaim is being determined. * * However, the cgroup that will own the folio is the one that - * is actually experiencing the refault event. + * is actually experiencing the refault event. Make sure the folio is + * locked to guarantee folio_memcg() stability throughout. */ + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); nr = folio_nr_pages(folio); memcg = folio_memcg(folio); pgdat = folio_pgdat(folio); @@ -540,7 +554,7 @@ void workingset_refault(struct folio *folio, void *shadow) mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
if (!workingset_test_recent(shadow, file, &workingset)) - goto out; + return;
folio_set_active(folio); workingset_age_nonresident(lruvec, nr); @@ -556,8 +570,6 @@ void workingset_refault(struct folio *folio, void *shadow) lru_note_cost_refault(folio); mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr); } -out: - rcu_read_unlock(); }
/** -- 2.50.1