From: Yosry Ahmed <yosryahmed@google.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Tejun Heo" <tj@kernel.org>, "Josef Bacik" <josef@toxicpanda.com>,
"Jens Axboe" <axboe@kernel.dk>,
"Zefan Li" <lizefan.x@bytedance.com>,
"Michal Hocko" <mhocko@kernel.org>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Shakeel Butt" <shakeelb@google.com>,
"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 6/9] memcg: sleep during flushing stats in safe contexts
Date: Tue, 28 Mar 2023 12:26:01 -0700 [thread overview]
Message-ID: <CAJD7tkYBO9QNZOyMt8WC0bd=wB9m1H3PHdxqPpWBx5HpUAS4Ug@mail.gmail.com> (raw)
In-Reply-To: <ZCM6m/4ujEqvFVsn@cmpxchg.org>
On Tue, Mar 28, 2023 at 12:06 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Tue, Mar 28, 2023 at 11:45:19AM -0700, Yosry Ahmed wrote:
> > On Tue, Mar 28, 2023 at 11:35 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> > > On Tue, Mar 28, 2023 at 06:16:35AM +0000, Yosry Ahmed wrote:
> > > > void mem_cgroup_flush_stats_ratelimited(void)
> > > > {
> > > > if (time_after64(jiffies_64, READ_ONCE(flush_next_time)))
> > > > - mem_cgroup_flush_stats();
> > > > + mem_cgroup_flush_stats_atomic();
> > > > +}
> > >
> > > This should probably be mem_cgroup_flush_stats_atomic_ratelimited().
> > >
> > > (Whee, kinda long, but that's alright. Very specialized caller...)
> >
> > It should, but the following patch makes it non-atomic anyway, so I
> > thought I wouldn't clutter the diff by renaming it here and then
> > reverting it back in the next patch.
> >
> > There is an argument for maintaining a clean history tho in case the
> > next patch is reverted separately (which is the reason I put it in a
> > separate patch to begin with) -- so perhaps I should rename it here to
> > mem_cgroup_flush_stats_atomic_ratelimited () and back to
> > mem_cgroup_flush_stats_ratelimited() in the next patch, just for
> > consistency?
>
> Sounds good to me. It's pretty minor churn.
Ack. Will do so for v2. Thanks!
>
> > > Btw, can you guys think of a reason against moving the threshold check
> > > into the common function? It would then apply to the time-limited
> > > flushes as well, but that shouldn't hurt anything. This would make the
> > > code even simpler:
> >
> > I think the point of having the threshold check outside the common
> > function is that the periodic flusher always flushes, regardless of
> > the threshold, to keep rstat flushing from critical contexts as cheap
> > as possible.
>
> Good point. Yeah, let's keep it separate then.
Agreed.
>
> > > > @@ -2845,7 +2845,7 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
> > > > * Flush the memory cgroup stats, so that we read accurate per-memcg
> > > > * lruvec stats for heuristics.
> > > > */
> > > > - mem_cgroup_flush_stats();
> > > > + mem_cgroup_flush_stats_atomic();
> > >
> > > I'm thinking this one could be non-atomic as well. It's called fairly
> > > high up in reclaim without any locks held.
> >
> > A later patch does exactly that. I put making the reclaim and refault
> > paths non-atomic in separate patches to easily revert them if we see a
> > regression. Let me know if this is too defensive and if you'd rather
> > have them squashed.
>
> No, good call. I should have just looked ahead first :-)
next prev parent reply other threads:[~2023-03-28 19:26 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
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 [this message]
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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