From: Mel Gorman <mgorman@techsingularity.net>
To: Vasily Averin <vvs@virtuozzo.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
Michal Hocko <mhocko@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, kernel@openvz.org,
Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0
Date: Tue, 12 Oct 2021 12:38:04 +0100 [thread overview]
Message-ID: <20211012113804.GT3959@techsingularity.net> (raw)
In-Reply-To: <f52c5cd3-9b74-0fd5-2b7b-83ca21c52b2a@virtuozzo.com>
On Tue, Oct 12, 2021 at 01:42:41PM +0300, Vasily Averin wrote:
> On 08.10.2021 14:47, Vlastimil Babka wrote:
> > On 10/8/21 11:24, Vasily Averin wrote:
> >> __alloc_pages_bulk can call __count_zid_vm_events and zone_statistics
> >> with nr_account = 0.
> >
> > But that's not a bug, right? Just an effective no-op that's not commonly
> > happening, so is it worth the check?
>
> Why not?
>
> Yes, it's not a bug, it just makes the kernel a bit more efficient in a very unlikely case.
At the cost of an additional branch in the likely case that may be
mispredicted.
> However, it looks strange and makes uninformed code reviewers like me worry about possible
> problems inside the affected functions. No one else calls these functions from 0.
>
The accounting functions should still work with a 0 delta.
--
Mel Gorman
SUSE Labs
prev parent reply other threads:[~2021-10-12 11:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 9:24 [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0 Vasily Averin
2021-10-08 9:24 ` Vasily Averin
[not found] ` <b2371951-bb8a-e62e-8d33-10830bbf6275-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2021-10-08 11:47 ` Vlastimil Babka
2021-10-08 11:47 ` Vlastimil Babka
2021-10-12 10:42 ` Vasily Averin
[not found] ` <f52c5cd3-9b74-0fd5-2b7b-83ca21c52b2a-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2021-10-12 11:09 ` David Hildenbrand
2021-10-12 11:09 ` David Hildenbrand
2021-10-12 12:02 ` Chris Down
2021-10-12 12:02 ` Chris Down
2021-10-12 11:38 ` Mel Gorman [this message]
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