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Mercier" Cc: Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Efly Young , android-mm@google.com, yuzhao@google.com, mkoutny@suse.com, Yosry Ahmed , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm: memcg: Use larger batches for proactive reclaim Message-ID: References: <20240202233855.1236422-1-tjmercier@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240202233855.1236422-1-tjmercier@google.com> X-Rspamd-Queue-Id: 555358000A X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: mspuy9k8tsf8unszk46zgckehfjc69g5 X-HE-Tag: 1707129645-778580 X-HE-Meta: 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 nOTNYf6Y CnIHmB0Hx96GLePoJXsr8Oem0XommqTbWCd9OfuJjsuC7IzGn2X7kr0fkjwHOHcuBwUh6gc/r8wIBwf5oy4FkVwq5tU5HzTZB0SYJNlqDnuFI6sLc4DIWEzylKQ7YQzYhwHVuVDYkQNUfeDAXpf4aeeUtaln97kdHE6mqcEZ/pY+UD5Tq1tUtpi7q/53QVWLzbATRkrwbLXcwe0sqjlynM/WAx1c4NtCsac+hhwb+MQiTWkjzfKcXI6Ft7jJCSjthe114Aert8rvStKKP6S5fSyIR3TC2L8KRTBCTxtT6x9Pb1M2tJIghu5+kpMd2KIreFFLZsImJ+EBtFqM= 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 02-02-24 23:38:54, T.J. Mercier wrote: > Before 388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactive > reclaim") we passed the number of pages for the reclaim request directly > 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. You have mentioned that in one of the previous emails but it is good to mention what is the source of that overhead for the future reference. > 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 while > maintaining reasonable throughput. These numbers are with MGLRU or the default reclaim implementation? > 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 proactive reclaim") > Signed-off-by: T.J. Mercier > Reviewed-by: Yosry Ahmed > Acked-by: Johannes Weiner > > --- > v3: Formatting fixes per Yosry Ahmed and Johannes Weiner. No functional > changes. > v2: Simplify the request size calculation per Johannes Weiner and Michal Koutný > > mm/memcontrol.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 46d8d02114cf..f6ab61128869 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6976,9 +6976,11 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > if (!nr_retries) > lru_add_drain_all(); > > + /* Will converge on zero, but reclaim enforces a minimum */ > + unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4; This doesn't fit into the existing coding style. I do not think there is a strong reason to go against it here. > + > reclaimed = try_to_free_mem_cgroup_pages(memcg, > - min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX), > - GFP_KERNEL, reclaim_options); > + batch_size, GFP_KERNEL, reclaim_options); Also with the increased reclaim target do we need something like this? diff --git a/mm/vmscan.c b/mm/vmscan.c index 4f9c854ce6cc..94794cf5ee9f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1889,7 +1889,7 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan, /* We are about to die and free our memory. Return now. */ if (fatal_signal_pending(current)) - return SWAP_CLUSTER_MAX; + return sc->nr_to_reclaim; } lru_add_drain(); > > if (!reclaimed && !nr_retries--) > return -EAGAIN; > -- > 2.43.0.594.gd9cf4e227d-goog -- Michal Hocko SUSE Labs