The patch titled
Subject: Revert "mm: vmscan: hold write lock to reparent shrinker nr_deferred"
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
revert-mm-vmscan-hold-write-lock-to-reparent-shrinker-nr_deferred.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-mm-vmscan-hold-write-lock-to-reparent-shrinker-nr_deferred.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: Revert "mm: vmscan: hold write lock to reparent shrinker nr_deferred"
Date: Fri, 9 Jun 2023 08:15:14 +0000
This reverts commit b3cabea3c9153fd42fe5cb851ac58b51ea2b32b8.
Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make
global slab shrink lockless"). The root cause is that SRCU has to be careful
to not frequently check for SRCU read-side critical section exits. Therefore,
even if no one is currently in the SRCU read-side critical section,
synchronize_srcu() cannot return quickly. That's why unregister_shrinker()
has become slower.
We will try to use the refcount+RCU method [2] proposed by Dave Chinner
to continue to re-implement the lockless slab shrink. Because there will
be other readers after reverting the shrinker_srcu related changes, so
it is better to restore to hold read lock to reparent shrinker nr_deferred.
[1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@xxxxxxxxx/
[2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@xxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20230609081518.3039120-4-qi.zheng@xxxxxxxxx
Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@xxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Kirill Tkhai <tkhai@xxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/vmscan.c~revert-mm-vmscan-hold-write-lock-to-reparent-shrinker-nr_deferred
+++ a/mm/vmscan.c
@@ -433,7 +433,7 @@ void reparent_shrinker_deferred(struct m
parent = root_mem_cgroup;
/* Prevent from concurrent shrinker_info expand */
- down_write(&shrinker_rwsem);
+ down_read(&shrinker_rwsem);
for_each_node(nid) {
child_info = shrinker_info_protected(memcg, nid);
parent_info = shrinker_info_protected(parent, nid);
@@ -442,7 +442,7 @@ void reparent_shrinker_deferred(struct m
atomic_long_add(nr, &parent_info->nr_deferred[i]);
}
}
- up_write(&shrinker_rwsem);
+ up_read(&shrinker_rwsem);
}
static bool cgroup_reclaim(struct scan_control *sc)
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex.patch
revert-mm-vmscan-remove-shrinker_rwsem-from-synchronize_shrinkers.patch
revert-mm-vmscan-hold-write-lock-to-reparent-shrinker-nr_deferred.patch
revert-mm-shrinkers-make-count-and-scan-in-shrinker-debugfs-lockless.patch
revert-mm-vmscan-add-shrinker_srcu_generation.patch
revert-mm-vmscan-make-memcg-slab-shrink-lockless.patch
revert-mm-vmscan-make-global-slab-shrink-lockless.patch
mm-vmscan-move-shrinker_debugfs_remove-before-synchronize_srcu.patch
