From: Tejun Heo <tj@kernel.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: "Alexander Viro" <viro@zeniv.linux.org.uk>,
"Christian Brauner" <brauner@kernel.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Michal Hocko" <mhocko@kernel.org>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Shakeel Butt" <shakeelb@google.com>,
"Muchun Song" <songmuchun@bytedance.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jan Kara" <jack@suse.cz>, "Jens Axboe" <axboe@kernel.dk>,
"Michal Koutný" <mkoutny@suse.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v5 1/5] writeback: move wb_over_bg_thresh() call outside lock section
Date: Fri, 5 May 2023 05:18:28 -1000 [thread overview]
Message-ID: <ZFUeRAYMJZQ7J7Ld@slm.duckdns.org> (raw)
In-Reply-To: <20230421174020.2994750-2-yosryahmed@google.com>
On Fri, Apr 21, 2023 at 05:40:16PM +0000, Yosry Ahmed wrote:
> wb_over_bg_thresh() calls mem_cgroup_wb_stats() which invokes an rstat
> flush, which can be expensive on large systems. Currently,
> wb_writeback() calls wb_over_bg_thresh() within a lock section, so we
> have to do the rstat flush atomically. On systems with a lot of
> cpus and/or cgroups, this can cause us to disable irqs for a long time,
> potentially causing problems.
>
> Move the call to wb_over_bg_thresh() outside the lock section in
> preparation to make the rstat flush in mem_cgroup_wb_stats() non-atomic.
> The list_empty(&wb->work_list) check should be okay outside the lock
> section of wb->list_lock as it is protected by a separate lock
> (wb->work_lock), and wb_over_bg_thresh() doesn't seem like it is
> modifying any of wb->b_* lists the wb->list_lock is protecting.
> Also, the loop seems to be already releasing and reacquring the
> lock, so this refactoring looks safe.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> Reviewed-by: Michal Koutný <mkoutny@suse.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
--
tejun
next prev parent reply other threads:[~2023-05-05 15:18 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-21 17:40 [PATCH v5 0/5] cgroup: eliminate atomic rstat flushing Yosry Ahmed
2023-04-21 17:40 ` [PATCH v5 1/5] writeback: move wb_over_bg_thresh() call outside lock section Yosry Ahmed
2023-04-24 17:16 ` Shakeel Butt
2023-05-05 15:18 ` Tejun Heo [this message]
2023-04-21 17:40 ` [PATCH v5 2/5] memcg: flush stats non-atomically in mem_cgroup_wb_stats() Yosry Ahmed
2023-05-05 15:19 ` Tejun Heo
2023-04-21 17:40 ` [PATCH v5 3/5] memcg: calculate root usage from global state Yosry Ahmed
2023-04-21 17:40 ` [PATCH v5 4/5] memcg: remove mem_cgroup_flush_stats_atomic() Yosry Ahmed
2023-04-21 17:40 ` [PATCH v5 5/5] cgroup: remove cgroup_rstat_flush_atomic() Yosry Ahmed
2023-04-24 17:17 ` Shakeel Butt
2023-05-05 15:20 ` Tejun Heo
2023-04-21 18:54 ` [PATCH v5 0/5] cgroup: eliminate atomic rstat flushing Yosry Ahmed
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