From: Shakeel Butt <shakeelb@google.com>
To: Daniel Dao <dqminh@cloudflare.com>, Ivan Babrou <ivan@cloudflare.com>
Cc: kernel-team <kernel-team@cloudflare.com>,
"Linux MM" <linux-mm@kvack.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Roman Gushchin" <guro@fb.com>, "Feng Tang" <feng.tang@intel.com>,
"Michal Hocko" <mhocko@kernel.org>,
"Hillf Danton" <hdanton@sina.com>,
"Michal Koutný" <mkoutny@suse.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: Re: Regression in workingset_refault latency on 5.15
Date: Wed, 23 Feb 2022 08:00:44 -0800 [thread overview]
Message-ID: <CALvZod76u0qXBzrCZ16j9xTVkPPvqyw9+4s2K67bVwB1fQHnPw@mail.gmail.com> (raw)
In-Reply-To: <CALvZod4+-q7ciz3A_-J0UWjQNe1P==WMyNNKFu4dqiy8oGisTQ@mail.gmail.com>
On Wed, Feb 23, 2022 at 7:57 AM Shakeel Butt <shakeelb@google.com> wrote:
>
> +Ivan Babrou
>
> Hi Daniel,
>
> On Wed, Feb 23, 2022 at 5:51 AM Daniel Dao <dqminh@cloudflare.com> wrote:
> >
> > Hi all,
> >
> > We are observing some regressions in workingset_refault on our newly upgraded
> > 5.15.19 nodes with zram as swap. This manifests in several ways:
> >
> > 1) Regression of workingset_refault duration observed in flamegraph
> >
> > We regularly collect flamegraphs for running services on the node. Since upgrade
> > to 5.15.19, we see that workingset_refault occupied a more significant part of
> > the service flamegraph (13%) with the following call trace
> >
> > workingset_refault+0x128
> > add_to_page_cache_lru+0x9f
> > page_cache_ra_unbounded+0x154
> > force_page_cache_ra+0xe2
> > filemap_get_pages+0xe9
> > filemap_read+0xa4
> > xfs_file_buffered_read+0x98
> > xfs_file_read_iter+0x6a
> > new_sync_read+0x118
> > vfs_read+0xf2
> > __x64_sys_pread64+0x89
> > do_syscall_64+0x3b
> > entry_SYSCALL_64_after_hwframe+0x44
> >
> > 2) Regression of userspace performance sensitive code
> >
> > We have some performance sensentive code running in userspace that have their
> > runtime measured by CLOCK_THREAD_CPUTIME_ID. They look roughly as:
> >
> > now = clock_gettime(CLOCK_THREAD_CPUTIME_ID)
> > func()
> > elapsed = clock_gettime(CLOCK_THREAD_CPUTIME_ID) - now
> >
> > Since 5.15 upgrade, we observed long `elapsed` in the range of 4-10ms much more
> > frequently than before. This went away after we disabled swap for the service
> > using `memory.swap.max=0` memcg configuration.
> >
> > The new thing in 5.15 workingset_refault seems to be introduction of
> > mem_cgroup_flush_stats()
> > by commit 1f828223b7991a228bc2aef837b78737946d44b2 (memcg: flush
> > lruvec stats in the
> > refault).
> >
> > Given that mem_cgroup_flush_stats can take quite a long time for us on the
> > standard systemd cgroupv2 hierrachy ( root / system.slice / workload.service )
> >
> > sudo /usr/share/bcc/tools/funcslower -m 10 -t mem_cgroup_flush_stats
> > Tracing function calls slower than 10 ms... Ctrl+C to quit.
> > TIME COMM PID LAT(ms) RVAL FUNC
> > 0.000000 <redacted> 804776 11.50 200
> > mem_cgroup_flush_stats
> > 0.343383 <redacted> 647496 10.58 200
> > mem_cgroup_flush_stats
> > 0.604309 <redacted> 804776 10.50 200
> > mem_cgroup_flush_stats
> > 1.230416 <redacted> 803293 10.01 200
> > mem_cgroup_flush_stats
> > 1.248442 <redacted> 646400 11.02 200
> > mem_cgroup_flush_stats
> >
> > could it be possible that workingset_refault in some unfortunate case can take
> > much longer than before such that it increases the time observed by
> > CLOCK_THREAD_CPUTIME_ID from userspace, or overall duration of
> > workingset_refault
> > observed by perf ?
>
> Ivan reported this issue last month and since then we have backported
> three patches to 5.15-stable to fix the issue. These got merged into
> 5.15.18. However you are reporting the issue is still present 5.15.19.
>
> Can you share a bit more detail on your hardware configuration (num of
> cpus) and if possible the flamegraph?
>
Also if you can reproduce the issue, can you try the patch at
https://lore.kernel.org/all/20210929235936.2859271-1-shakeelb@google.com/
?
next prev parent reply other threads:[~2022-02-23 16:00 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-23 13:51 Regression in workingset_refault latency on 5.15 Daniel Dao
2022-02-23 15:57 ` Shakeel Butt
2022-02-23 16:00 ` Shakeel Butt [this message]
2022-02-23 17:07 ` Daniel Dao
2022-02-23 17:36 ` Shakeel Butt
2022-02-23 19:28 ` Ivan Babrou
2022-02-23 20:28 ` Shakeel Butt
2022-02-23 21:16 ` Ivan Babrou
2022-02-24 14:46 ` Daniel Dao
2022-02-24 16:58 ` Shakeel Butt
2022-02-24 17:34 ` Daniel Dao
2022-02-24 18:00 ` Shakeel Butt
2022-02-24 18:52 ` Shakeel Butt
2022-02-25 10:23 ` Daniel Dao
2022-02-25 17:08 ` Ivan Babrou
2022-02-25 17:22 ` Shakeel Butt
2022-02-25 18:03 ` Michal Koutný
2022-02-25 18:08 ` Ivan Babrou
2022-02-28 23:09 ` Shakeel Butt
2022-02-28 23:34 ` Ivan Babrou
2022-02-28 23:43 ` Shakeel Butt
2022-03-02 0:48 ` Ivan Babrou
2022-03-02 2:50 ` Shakeel Butt
2022-03-02 3:40 ` Ivan Babrou
2022-03-02 22:33 ` Ivan Babrou
2022-03-03 2:32 ` Shakeel Butt
2022-03-03 2:35 ` Shakeel Butt
2022-03-04 0:21 ` Ivan Babrou
2022-03-04 1:05 ` Shakeel Butt
2022-03-04 1:12 ` Ivan Babrou
2022-03-02 11:49 ` Frank Hofmann
2022-03-02 15:52 ` Shakeel Butt
2022-03-02 10:08 ` Michal Koutný
2022-03-02 15:53 ` Shakeel Butt
2022-03-02 17:28 ` Ivan Babrou
2022-02-24 9:22 ` Thorsten Leemhuis
2022-04-11 10:17 ` Regression in workingset_refault latency on 5.15 #forregzbot Thorsten Leemhuis
2022-05-16 12:51 ` Thorsten Leemhuis
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