The patch titled
Subject: mm: workingset: move the stats flush into workingset_test_recent()
has been added to the -mm mm-unstable branch. Its filename is
mm-workingset-move-the-stats-flush-into-workingset_test_recent.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-workingset-move-the-stats-flush-into-workingset_test_recent.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Subject: mm: workingset: move the stats flush into workingset_test_recent()
Date: Tue, 10 Oct 2023 03:21:15 +0000
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/20231010032117.1577496-5-yosryahmed@xxxxxxxxxx
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Tested-by: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Ivan Babrou <ivan@xxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Tejun heo <tj@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/workingset.c | 36 ++++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)
--- a/mm/workingset.c~mm-workingset-move-the-stats-flush-into-workingset_test_recent
+++ a/mm/workingset.c
@@ -425,8 +425,16 @@ bool workingset_test_recent(void *shadow
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
* 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
}
}
+ mem_cgroup_put(eviction_memcg);
return refault_distance <= workingset_size;
}
@@ -519,19 +536,16 @@ void workingset_refault(struct folio *fo
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 *fo
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 *fo
lru_note_cost_refault(folio);
mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
}
-out:
- rcu_read_unlock();
}
/**
_
Patches currently in -mm which might be from yosryahmed@xxxxxxxxxx are
mm-memcg-refactor-page-state-unit-helpers.patch
mm-memcg-normalize-the-value-passed-into-memcg_rstat_updated.patch
mm-memcg-change-flush_next_time-to-flush_last_time.patch
mm-memcg-move-vmstats-structs-definition-above-flushing-code.patch
mm-memcg-make-stats-flushing-threshold-per-memcg.patch
mm-workingset-move-the-stats-flush-into-workingset_test_recent.patch
mm-memcg-restore-subtree-stats-flushing.patch
