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From: David Hildenbrand <david@redhat.com>
To: Vasily Averin <vvs@virtuozzo.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Michal Hocko <mhocko@kernel.org>
Cc: 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,
	Mel Gorman <mgorman@techsingularity.net>,
	Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0
Date: Tue, 12 Oct 2021 13:09:27 +0200	[thread overview]
Message-ID: <0a707990-f12c-3c60-2a96-e1d531e100a6@redhat.com> (raw)
In-Reply-To: <f52c5cd3-9b74-0fd5-2b7b-83ca21c52b2a@virtuozzo.com>

On 12.10.21 12:42, 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.
> 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.
>   

If it's not a BUG we'd better leave "Fixes:" tags away., it tends to 
confuse people looking for actual BUGs.

I'm also not sure if this micro-optimization is worth it. "bit more 
efficient in a very unlikely case" doesn't sound very compelling ... and 
personally I'd assume accounting functions can deal with a delta of 0.

-- 
Thanks,

David / dhildenb



  reply	other threads:[~2021-10-12 11:09 UTC|newest]

Thread overview: 6+ 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 11:47 ` Vlastimil Babka
2021-10-12 10:42   ` Vasily Averin
2021-10-12 11:09     ` David Hildenbrand [this message]
2021-10-12 11:38     ` Mel Gorman
2021-10-12 12:02     ` Chris Down

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