From: Yosry Ahmed <yosryahmed@google.com>
To: Shakeel Butt <shakeelb@google.com>
Cc: "Oliver Sang" <oliver.sang@intel.com>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Feng Tang" <feng.tang@intel.com>,
"oe-lkp@lists.linux.dev" <oe-lkp@lists.linux.dev>,
lkp <lkp@intel.com>,
"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Huang, Ying" <ying.huang@intel.com>,
"Yin, Fengwei" <fengwei.yin@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Michal Hocko" <mhocko@kernel.org>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Muchun Song" <muchun.song@linux.dev>,
"Ivan Babrou" <ivan@cloudflare.com>, "Tejun Heo" <tj@kernel.org>,
"Michal Koutný" <mkoutny@suse.com>,
"Waiman Long" <longman@redhat.com>,
"kernel-team@cloudflare.com" <kernel-team@cloudflare.com>,
"Wei Xu" <weixugc@google.com>, "Greg Thelen" <gthelen@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Domenico Cerasuolo" <cerasuolodomenico@gmail.com>
Subject: Re: [PATCH v2 3/5] mm: memcg: make stats flushing threshold per-memcg
Date: Wed, 25 Oct 2023 11:36:13 -0700 [thread overview]
Message-ID: <CAJD7tkaw1bFDgC1dfbuuCkyLToXRO2T2T7OuMt2fbfEKisP_4Q@mail.gmail.com> (raw)
In-Reply-To: <CALvZod5V-Ag5avAewE2nFp8__J6b_WqHuQw5=F70OPQrGNjfVw@mail.gmail.com>
On Wed, Oct 25, 2023 at 10:06 AM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Tue, Oct 24, 2023 at 11:23 PM Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> [...]
> >
> > Thanks Oliver for running the numbers. If I understand correctly the
> > will-it-scale.fallocate1 microbenchmark is the only one showing
> > significant regression here, is this correct?
> >
> > In my runs, other more representative microbenchmarks benchmarks like
> > netperf and will-it-scale.page_fault* show minimal regression. I would
> > expect practical workloads to have high concurrency of page faults or
> > networking, but maybe not fallocate/ftruncate.
> >
> > Oliver, in your experience, how often does such a regression in such a
> > microbenchmark translate to a real regression that people care about?
> > (or how often do people dismiss it?)
> >
> > I tried optimizing this further for the fallocate/ftruncate case but
> > without luck. I even tried moving stats_updates into cgroup core
> > (struct cgroup_rstat_cpu) to reuse the existing loop in
> > cgroup_rstat_updated() -- but it somehow made it worse.
> >
> > On the other hand, we do have some machines in production running this
> > series together with a previous optimization for non-hierarchical
> > stats [1] on an older kernel, and we do see significant reduction in
> > cpu time spent on reading the stats. Domenico did a similar experiment
> > with only this series and reported similar results [2].
> >
> > Shakeel, Johannes, (and other memcg folks), I personally think the
> > benefits here outweigh a regression in this particular benchmark, but
> > I am obviously biased. What do you think?
> >
> > [1]https://lore.kernel.org/lkml/20230726153223.821757-2-yosryahmed@google.com/
> > [2]https://lore.kernel.org/lkml/CAFYChMv_kv_KXOMRkrmTN-7MrfgBHMcK3YXv0dPYEL7nK77e2A@mail.gmail.com/
>
> I still am not convinced of the benefits outweighing the regression
> but I would not block this. So, let's do this, skip this open window,
> get the patch series reviewed and hopefully we can work together on
> fixing that regression and we can make an informed decision of
> accepting the regression for this series for the next cycle.
Skipping this open window sounds okay to me.
FWIW, I think with this patch series we can keep the old behavior
(roughly) and hide the changes behind a tunable (config option or
sysfs file). I think the only changes that need to be done to the code
to approximate the previous behavior are:
- Use root when updating the pending stats in memcg_rstat_updated()
instead of the passed memcg.
- Use root in mem_cgroup_flush_stats() instead of the passed memcg.
- Use mutex_trylock() instead of mutex_lock() in mem_cgroup_flush_stats().
So I think it should be doable to hide most changes behind a tunable,
but let's not do this unless necessary.
next prev parent reply other threads:[~2023-10-25 18:36 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 3:21 [PATCH v2 0/5] mm: memcg: subtree stats flushing and thresholds Yosry Ahmed
2023-10-10 3:21 ` [PATCH v2 1/5] mm: memcg: change flush_next_time to flush_last_time Yosry Ahmed
2023-10-10 3:21 ` [PATCH v2 2/5] mm: memcg: move vmstats structs definition above flushing code Yosry Ahmed
2023-10-10 3:21 ` [PATCH v2 3/5] mm: memcg: make stats flushing threshold per-memcg Yosry Ahmed
2023-10-10 3:24 ` Yosry Ahmed
2023-10-10 20:45 ` Shakeel Butt
2023-10-10 21:02 ` Yosry Ahmed
2023-10-10 22:21 ` Yosry Ahmed
2023-10-11 0:36 ` Shakeel Butt
2023-10-11 1:48 ` Yosry Ahmed
2023-10-11 12:45 ` Shakeel Butt
2023-10-12 3:13 ` Yosry Ahmed
2023-10-12 8:01 ` Yosry Ahmed
2023-10-12 8:04 ` Yosry Ahmed
2023-10-12 13:29 ` Johannes Weiner
2023-10-12 23:28 ` Yosry Ahmed
2023-10-13 2:33 ` Johannes Weiner
2023-10-13 2:38 ` Yosry Ahmed
2023-10-12 13:35 ` Shakeel Butt
2023-10-12 15:10 ` Yosry Ahmed
2023-10-12 21:05 ` Yosry Ahmed
2023-10-12 21:16 ` Shakeel Butt
2023-10-12 21:19 ` Yosry Ahmed
2023-10-12 21:38 ` Shakeel Butt
2023-10-12 22:23 ` Yosry Ahmed
2023-10-14 23:08 ` Andrew Morton
2023-10-16 18:42 ` Yosry Ahmed
2023-10-17 23:52 ` Yosry Ahmed
2023-10-18 8:22 ` Oliver Sang
2023-10-18 8:54 ` Yosry Ahmed
2023-10-20 16:17 ` kernel test robot
2023-10-20 17:23 ` Shakeel Butt
2023-10-20 17:42 ` Yosry Ahmed
2023-10-23 1:25 ` Feng Tang
2023-10-23 18:25 ` Yosry Ahmed
2023-10-24 2:13 ` Yosry Ahmed
2023-10-24 6:56 ` Oliver Sang
2023-10-24 7:14 ` Yosry Ahmed
2023-10-25 6:09 ` Oliver Sang
2023-10-25 6:22 ` Yosry Ahmed
2023-10-25 17:06 ` Shakeel Butt
2023-10-25 18:36 ` Yosry Ahmed [this message]
2023-10-10 3:21 ` [PATCH v2 4/5] mm: workingset: move the stats flush into workingset_test_recent() Yosry Ahmed
2023-10-10 3:21 ` [PATCH v2 5/5] mm: memcg: restore subtree stats flushing Yosry Ahmed
2023-10-10 16:48 ` [PATCH v2 0/5] mm: memcg: subtree stats flushing and thresholds domenico cerasuolo
2023-10-10 19:01 ` Yosry Ahmed
2023-10-18 21:12 ` Andrew Morton
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