From: Shakeel Butt <shakeelb@google.com> To: Yosry Ahmed <yosryahmed@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 12:28:00 -0700 [thread overview] Message-ID: <CALvZod4Gsngc6MjXdk4s5+ePVjsgcVppdRmsQovN6gSrxzdbfA@mail.gmail.com> (raw) In-Reply-To: <CAJD7tkYo=CeXJPUi_KxjzC0QCxC2qd_J2_FQi_aXh7svD8u60A@mail.gmail.com> 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.
WARNING: multiple messages have this Message-ID (diff)
From: Shakeel Butt <shakeelb@google.com> To: Yosry Ahmed <yosryahmed@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 12:28:00 -0700 [thread overview] Message-ID: <CALvZod4Gsngc6MjXdk4s5+ePVjsgcVppdRmsQovN6gSrxzdbfA@mail.gmail.com> (raw) In-Reply-To: <CAJD7tkYo=CeXJPUi_KxjzC0QCxC2qd_J2_FQi_aXh7svD8u60A@mail.gmail.com> 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.
next prev parent reply other threads:[~2023-03-28 19:28 UTC|newest] Thread overview: 68+ 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 ` Yosry Ahmed 2023-03-28 6:16 ` [PATCH v1 1/9] cgroup: rename cgroup_rstat_flush_"irqsafe" to "atomic" Yosry Ahmed 2023-03-28 6:16 ` Yosry Ahmed 2023-03-28 13:24 ` Shakeel Butt 2023-03-28 13:24 ` Shakeel Butt 2023-03-28 17:42 ` Johannes Weiner 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 13:25 ` Shakeel Butt 2023-03-28 17:42 ` Johannes Weiner 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 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 14:59 ` Shakeel Butt 2023-03-28 17:49 ` Johannes Weiner 2023-03-28 18:59 ` Yosry Ahmed 2023-03-28 18:59 ` Yosry Ahmed 2023-03-28 22:18 ` 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 14:15 ` Shakeel Butt 2023-03-28 18:52 ` Yosry Ahmed 2023-03-28 18:52 ` Yosry Ahmed 2023-03-28 19:28 ` Shakeel Butt [this message] 2023-03-28 19:28 ` Shakeel Butt 2023-03-28 19:34 ` Yosry Ahmed 2023-03-28 19:34 ` Yosry Ahmed 2023-03-28 19:42 ` Yosry Ahmed 2023-03-28 17:53 ` Johannes Weiner 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 15:09 ` Shakeel Butt 2023-03-28 18:35 ` Johannes Weiner 2023-03-28 18:45 ` Yosry Ahmed 2023-03-28 18:45 ` Yosry Ahmed 2023-03-28 19:06 ` Johannes Weiner 2023-03-28 19:06 ` Johannes Weiner 2023-03-28 19:26 ` Yosry Ahmed 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 15:18 ` Shakeel Butt 2023-03-28 18:47 ` Johannes Weiner 2023-03-28 18:47 ` Johannes Weiner 2023-03-28 19:25 ` Yosry Ahmed 2023-03-28 18:43 ` Johannes Weiner 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 6:16 ` Yosry Ahmed 2023-03-28 15:19 ` Shakeel Butt 2023-03-28 15:19 ` Shakeel Butt 2023-03-28 19:01 ` Yosry Ahmed 2023-03-28 19:01 ` Yosry Ahmed 2023-03-28 19:29 ` Shakeel Butt 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 15:20 ` Shakeel Butt 2023-03-28 18:50 ` Johannes Weiner
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