From: Vasily Averin <vvs@virtuozzo.com>
To: 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 13:42:41 +0300 [thread overview]
Message-ID: <f52c5cd3-9b74-0fd5-2b7b-83ca21c52b2a@virtuozzo.com> (raw)
In-Reply-To: <29155011-f884-b0e5-218e-911039568acb@suse.cz>
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.
>> Fixes: 3e23060b2d0b ("mm/page_alloc: batch the accounting updates in the bulk allocator")
>> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
>> ---
>> mm/page_alloc.c | 7 ++++---
>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 602819a232e5..e67113452ee8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5364,9 +5364,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>> }
>>
>> local_unlock_irqrestore(&pagesets.lock, flags);
>> -
>> - __count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
>> - zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
>> + if (nr_account) {
>> + __count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
>> + zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
>> + }
>> if (objcg)
>> memcg_bulk_post_charge_hook(objcg, nr_pre_charge - nr_account);
>>
>>
>
next prev parent reply other threads:[~2021-10-12 10:43 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 [this message]
2021-10-12 11:09 ` David Hildenbrand
2021-10-12 11:38 ` Mel Gorman
2021-10-12 12:02 ` Chris Down
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