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Mercier" Date: Fri, 2 Feb 2024 14:29:17 -0800 Message-ID: Subject: Re: [PATCH v2] mm: memcg: Use larger batches for proactive reclaim To: Yosry Ahmed Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Efly Young , android-mm@google.com, yuzhao@google.com, mkoutny@suse.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: C8E2A120014 X-Stat-Signature: pid33pf3yrico4dh968rum6or1wwue6z X-HE-Tag: 1706912969-820178 X-HE-Meta: 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 QX/a4QvG 4CNObFSPypJWbfQT8WYbRjSjAMOf8O3NVPwzDpK1R1oD+yJ1Lfg4xJFIywzTcIEC7LF7l8xliIp3QguF7aAJ2v8xirnejV0c2T+essyW5knTSOB6NP8g0GmDQTo57j9CB7Xhl4k4LReM+1A5uvKHxTg3tHYwkjouhv8+Y4Nh8tiuX+1pEt37GZg3XJg+ErnWj0FkN7PmPvlUS72fzjSfSuj/fgfVZdu9vC78P4CFeXdDFw640ia4CAws+k0BaL0oyQmjk0zK2rA0XMSkNAhHmLYiPzr7zTQGyVUoV 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: List-Subscribe: List-Unsubscribe: On Fri, Feb 2, 2024 at 2:14=E2=80=AFPM Yosry Ahmed = wrote: > > On Fri, Feb 2, 2024 at 2:10=E2=80=AFPM T.J. Mercier wrote: > > > > Before 388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactive > > reclaim") we passed the number of pages for the reclaim request directl= y > > to try_to_free_mem_cgroup_pages, which could lead to significant > > overreclaim. After 0388536ac291 the number of pages was limited to a > > maximum 32 (SWAP_CLUSTER_MAX) to reduce the amount of overreclaim. > > However such a small batch size caused a regression in reclaim > > performance due to many more reclaim start/stop cycles inside > > memory_reclaim. > > > > Reclaim tries to balance nr_to_reclaim fidelity with fairness across > > nodes and cgroups over which the pages are spread. As such, the bigger > > the request, the bigger the absolute overreclaim error. Historic > > in-kernel users of reclaim have used fixed, small sized requests to > > approach an appropriate reclaim rate over time. When we reclaim a user > > request of arbitrary size, use decaying batch sizes to manage error whi= le > > maintaining reasonable throughput. > > > > root - full reclaim pages/sec time (sec) > > pre-0388536ac291 : 68047 10.46 > > post-0388536ac291 : 13742 inf > > (reclaim-reclaimed)/4 : 67352 10.51 > > > > /uid_0 - 1G reclaim pages/sec time (sec) overreclaim (MiB) > > pre-0388536ac291 : 258822 1.12 107.8 > > post-0388536ac291 : 105174 2.49 3.5 > > (reclaim-reclaimed)/4 : 233396 1.12 -7.4 > > > > /uid_0 - full reclaim pages/sec time (sec) > > pre-0388536ac291 : 72334 7.09 > > post-0388536ac291 : 38105 14.45 > > (reclaim-reclaimed)/4 : 72914 6.96 > > > > Fixes: 0388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactiv= e reclaim") > > Signed-off-by: T.J. Mercier > > LGTM with a nit below: > Reviewed-by: Yosry Ahmed Thanks > > > > --- > > v2: Simplify the request size calculation per Johannes Weiner and Micha= l Koutn=C3=BD > > > > mm/memcontrol.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 46d8d02114cf..e6f921555e07 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -6965,6 +6965,9 @@ static ssize_t memory_reclaim(struct kernfs_open_= file *of, char *buf, > > while (nr_reclaimed < nr_to_reclaim) { > > unsigned long reclaimed; > > > > + /* Will converge on zero, but reclaim enforces a minimu= m */ > > + unsigned long batch_size =3D (nr_to_reclaim - nr_reclai= med) / 4; > > + > > if (signal_pending(current)) > > return -EINTR; > > > > @@ -6977,7 +6980,7 @@ static ssize_t memory_reclaim(struct kernfs_open_= file *of, char *buf, > > lru_add_drain_all(); > > > > reclaimed =3D try_to_free_mem_cgroup_pages(memcg, > > - min(nr_to_reclaim - nr_reclaime= d, SWAP_CLUSTER_MAX), > > + batch_size, > > GFP_KERNEL, reclaim_options); > > I think the above two lines should now fit into one. It goes out to 81 characters. I wasn't brave enough, even though the 80 char limit is no more. :) This takes it out to 100 but gets rid of batch_size if folks are ok with it= : reclaimed =3D try_to_free_mem_cgroup_pages(memcg, - min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX), + /* Will converge on zero, but reclaim enforces a minimum */ + (nr_to_reclaim - nr_reclaimed) / 4, GFP_KERNEL, reclaim_options);