mm/mglru: clean up workingset

Patch series "mm/mglru: performance optimizations", v4.

This series improves performance for some previously reported test cases. 
Most of the code changes gathered here has been floating on the mailing
list [1][2].  They are now properly organized and have gone through
various benchmarks on client and server devices, including Android, FIO,
memcached, multiple VMs and MongoDB.

In addition to the syzbot regressions fixed in v2 [3] and v3 [4], this
version fixes two more regressions: one reported by Oliver Sang [5] and
the other by Barry Song.

[1] https://lore.kernel.org/CAOUHufahuWcKf5f1Sg3emnqX+cODuR=2TQo7T4Gr-QYLujn4RA@mail.gmail.com/
[2] https://lore.kernel.org/CAOUHufawNerxqLm7L9Yywp3HJFiYVrYO26ePUb1jH-qxNGWzyA@mail.gmail.com/
[3] https://lore.kernel.org/[email protected]/
[4] https://lore.kernel.org/[email protected]/
[5] https://lore.kernel.org/[email protected]/


This patch (of 7):

Move VM_BUG_ON_FOLIO() to cover both the default and MGLRU paths.  Also
use a pair of rcu_read_lock() and rcu_read_unlock() within each path, to
improve readability.

This change should not have any side effects.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yu Zhao <[email protected]>
Tested-by: Kalesh Singh <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: David Stevens <[email protected]>
Cc: Kairui Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: yuzhaogoogle

mm/workingset.c

@@ -428,17 +428,17 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset,
 	struct pglist_data *pgdat;
 	unsigned long eviction;
 
-	rcu_read_lock();
-
 	if (lru_gen_enabled()) {
-		bool recent = lru_gen_test_recent(shadow, file,
-				&eviction_lruvec, &eviction, workingset);
+		bool recent;
 
+		rcu_read_lock();
+		recent = lru_gen_test_recent(shadow, file, &eviction_lruvec,
+					     &eviction, workingset);
 		rcu_read_unlock();
 		return recent;
 	}
 
-
+	rcu_read_lock();
 	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
 	eviction <<= bucket_order;
 
@@ -459,14 +459,12 @@ 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 || !mem_cgroup_tryget(eviction_memcg))) {
-		rcu_read_unlock();
-		return false;
-	}
-
+	if (!mem_cgroup_tryget(eviction_memcg))
+		eviction_memcg = NULL;
 	rcu_read_unlock();
 
+	if (!mem_cgroup_disabled() && !eviction_memcg)
+		return false;
 	/*
 	 * Flush stats (and potentially sleep) outside the RCU read section.
 	 *
@@ -544,6 +542,8 @@ void workingset_refault(struct folio *folio, void *shadow)
 	bool workingset;
 	long nr;
 
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
 	if (lru_gen_enabled()) {
 		lru_gen_refault(folio, shadow);
 		return;
@@ -558,7 +558,6 @@ void workingset_refault(struct folio *folio, void *shadow)
 	 * 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);