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Mon, 24 Apr 2023 10:16:45 -0700 (PDT) MIME-Version: 1.0 References: <20230421174020.2994750-1-yosryahmed@google.com> <20230421174020.2994750-2-yosryahmed@google.com> In-Reply-To: <20230421174020.2994750-2-yosryahmed@google.com> From: Shakeel Butt Date: Mon, 24 Apr 2023 10:16:34 -0700 Message-ID: Subject: Re: [PATCH v5 1/5] writeback: move wb_over_bg_thresh() call outside lock section To: Yosry Ahmed Cc: Alexander Viro , Christian Brauner , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , Tejun Heo , Jan Kara , Jens Axboe , =?UTF-8?Q?Michal_Koutn=C3=BD?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 51A1F120025 X-Stat-Signature: 4idc4hyyqxarfqisttytsyignx8jt6yu X-HE-Tag: 1682356606-739481 X-HE-Meta: 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 rniqW6tx 4xF1MldyTZ1cQ0TIbW6kW9o60N7+qzFsyXy+xNP+51FgQfmhgdDTHF7PHldk1hjU9yOAKWKObohVhaJC1E7DQS7+kK69qAAWJtP+cCjAHPuygoNoe6QSSq7HBzRTzoSi0uFXOeX/lDGU9y3b9SZY2go+F1trMWU5q6DtiNUTvGikoPXNdWBVP0vdNpW6wA/F9dH8HIagIHok5/58HZzc2EECBndy0nDwGECY7R/s+hJlX5TXf32YZrOR7xuUvviXvKeAq4ZzkriX+gha/fV2mynVzDkLq1UzqqmtGLMXQDOSfHUSuETiZzXe1aC2GUgT4IgVFfQ5uCypDlm5ndnneZshmJostloSyM5TCj+vg6S2P3qk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 21, 2023 at 10:40=E2=80=AFAM 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 > Reviewed-by: Michal Koutn=C3=BD > Reviewed-by: Jan Kara Acked-by: Shakeel Butt