From: Yosry Ahmed <yosryahmed@google.com>
To: Shakeel Butt <shakeelb@google.com>
Cc: "Tejun Heo" <tj@kernel.org>, "Josef Bacik" <josef@toxicpanda.com>,
"Jens Axboe" <axboe@kernel.dk>,
"Zefan Li" <lizefan.x@bytedance.com>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Michal Hocko" <mhocko@kernel.org>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Muchun Song" <muchun.song@linux.dev>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Michal Koutný" <mkoutny@suse.com>,
"Vasily Averin" <vasily.averin@linux.dev>,
cgroups@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
bpf@vger.kernel.org
Subject: Re: [PATCH v1 5/9] memcg: replace stats_flush_lock with an atomic
Date: Tue, 28 Mar 2023 12:34:15 -0700 [thread overview]
Message-ID: <CAJD7tkb_YA3fvo3LgCzR+X-b-r-AmAR68hNR=xT7B6TJfBa54A@mail.gmail.com> (raw)
In-Reply-To: <CALvZod4Gsngc6MjXdk4s5+ePVjsgcVppdRmsQovN6gSrxzdbfA@mail.gmail.com>
On Tue, Mar 28, 2023 at 12:28 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Tue, Mar 28, 2023 at 11:53 AM Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> [...]
> > > > + if (atomic_xchg(&stats_flush_ongoing, 1))
> > >
> > > Have you profiled this? I wonder if we should replace the above with
> > >
> > > if (atomic_read(&stats_flush_ongoing) || atomic_xchg(&stats_flush_ongoing, 1))
> >
> > I profiled the entire series with perf and I haven't noticed a notable
> > difference between before and after the patch series -- but maybe some
> > specific access patterns cause a regression, not sure.
> >
> > Does an atomic_cmpxchg() satisfy the same purpose? it's easier to read
> > / more concise I guess.
> >
> > Something like
> >
> > if (atomic_cmpxchg(&stats_flush_ongoing, 0, 1))
> >
> > WDYT?
> >
>
> No, I don't think cmpxchg will be any different from xchg(). On x86,
> the cmpxchg will always write to stats_flush_ongoing and depending on
> the comparison result, it will either be 0 or 1 here.
>
> If you see the implementation of queued_spin_trylock(), it does the
> same as well.
Interesting. I thought cmpxchg by definition will compare first and
only do the write if stats_flush_ongoing == 0 in this case.
I thought queued_spin_trylock() was doing an atomic_read() first to
avoid the LOCK instruction unnecessarily the lock is held by someone
else.
next prev parent reply other threads:[~2023-03-28 19:35 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-28 6:16 [PATCH v1 0/9] memcg: make rstat flushing irq and sleep friendly Yosry Ahmed
2023-03-28 6:16 ` [PATCH v1 1/9] cgroup: rename cgroup_rstat_flush_"irqsafe" to "atomic" Yosry Ahmed
2023-03-28 13:24 ` Shakeel Butt
2023-03-28 17:42 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 2/9] memcg: rename mem_cgroup_flush_stats_"delayed" to "ratelimited" Yosry Ahmed
2023-03-28 13:25 ` Shakeel Butt
2023-03-28 17:42 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 3/9] memcg: do not flush stats in irq context Yosry Ahmed
2023-03-28 13:26 ` Shakeel Butt
2023-03-28 17:43 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 4/9] cgroup: rstat: add WARN_ON_ONCE() if flushing outside task context Yosry Ahmed
2023-03-28 14:59 ` Shakeel Butt
2023-03-28 17:49 ` Johannes Weiner
2023-03-28 18:59 ` Yosry Ahmed
2023-03-28 22:18 ` Yosry Ahmed
2023-03-28 6:16 ` [PATCH v1 5/9] memcg: replace stats_flush_lock with an atomic Yosry Ahmed
2023-03-28 14:15 ` Shakeel Butt
2023-03-28 18:52 ` Yosry Ahmed
2023-03-28 19:28 ` Shakeel Butt
2023-03-28 19:34 ` Yosry Ahmed [this message]
2023-03-28 19:42 ` Yosry Ahmed
2023-03-28 17:53 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 6/9] memcg: sleep during flushing stats in safe contexts Yosry Ahmed
2023-03-28 15:09 ` Shakeel Butt
2023-03-28 18:35 ` Johannes Weiner
2023-03-28 18:45 ` Yosry Ahmed
2023-03-28 19:06 ` Johannes Weiner
2023-03-28 19:26 ` Yosry Ahmed
2023-03-28 6:16 ` [PATCH v1 7/9] workingset: memcg: sleep when flushing stats in workingset_refault() Yosry Ahmed
2023-03-28 15:18 ` Shakeel Butt
2023-03-28 18:47 ` Johannes Weiner
2023-03-28 19:25 ` Yosry Ahmed
2023-03-28 18:43 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 8/9] vmscan: memcg: sleep when flushing stats during reclaim Yosry Ahmed
2023-03-28 15:19 ` Shakeel Butt
2023-03-28 19:01 ` Yosry Ahmed
2023-03-28 19:29 ` Shakeel Butt
2023-03-28 18:49 ` Johannes Weiner
2023-03-28 6:16 ` [PATCH v1 9/9] memcg: do not modify rstat tree for zero updates Yosry Ahmed
2023-03-28 15:20 ` Shakeel Butt
2023-03-28 18:50 ` Johannes Weiner
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