The patch titled
Subject: cgroup, memcg, writeback: drop spurious rcu locking around mem_cgroup_css_from_page()
has been added to the -mm tree. Its filename is
cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page.patch
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------------------------------------------------------
From: Tejun Heo <tj@xxxxxxxxxx>
Subject: cgroup, memcg, writeback: drop spurious rcu locking around mem_cgroup_css_from_page()
In earlier versions, mem_cgroup_css_from_page() could return non-root css
on a legacy hierarchy which can go away and required rcu locking; however,
the eventual version simply returns the root cgroup if memcg is on a
legacy hierarchy and thus doesn't need rcu locking around or in it.
Remove spurious rcu lockings.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 2 --
mm/memcontrol.c | 3 ---
2 files changed, 5 deletions(-)
diff -puN fs/fs-writeback.c~cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page fs/fs-writeback.c
--- a/fs/fs-writeback.c~cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page
+++ a/fs/fs-writeback.c
@@ -677,9 +677,7 @@ void wbc_account_io(struct writeback_con
if (!wbc->wb)
return;
- rcu_read_lock();
id = mem_cgroup_css_from_page(page)->id;
- rcu_read_unlock();
if (id == wbc->wb_id) {
wbc->wb_bytes += bytes;
diff -puN mm/memcontrol.c~cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page mm/memcontrol.c
--- a/mm/memcontrol.c~cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page
+++ a/mm/memcontrol.c
@@ -382,14 +382,11 @@ struct cgroup_subsys_state *mem_cgroup_c
{
struct mem_cgroup *memcg;
- rcu_read_lock();
-
memcg = page->mem_cgroup;
if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
memcg = root_mem_cgroup;
- rcu_read_unlock();
return &memcg->css;
}
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
cgroup-memcg-writeback-drop-spurious-rcu-locking-around-mem_cgroup_css_from_page.patch
printk-do-cond_resched-between-lines-while-outputting-to-consoles.patch
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