From: Mel Gorman <mgorman@techsingularity.net>
To: Michal Hocko <mhocko@kernel.org>
Cc: Jia He <hejianet@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Taku Izumi <izumi.taku@jp.fujitsu.com>
Subject: Re: [PATCH RFC 1/1] mm, page_alloc: fix incorrect zone_statistics data
Date: Tue, 20 Dec 2016 13:10:40 +0000 [thread overview]
Message-ID: <20161220131040.f5ga5426dduh3mhu@techsingularity.net> (raw)
In-Reply-To: <20161220091814.GC3769@dhcp22.suse.cz>
On Tue, Dec 20, 2016 at 10:18:14AM +0100, Michal Hocko wrote:
> On Mon 12-12-16 13:59:07, Jia He wrote:
> > In commit b9f00e147f27 ("mm, page_alloc: reduce branches in
> > zone_statistics"), it reconstructed codes to reduce the branch miss rate.
> > Compared with the original logic, it assumed if !(flag & __GFP_OTHER_NODE)
> > z->node would not be equal to preferred_zone->node. That seems to be
> > incorrect.
>
> I am sorry but I have hard time following the changelog. It is clear
> that you are trying to fix a missed NUMA_{HIT,OTHER} accounting
> but it is not really clear when such thing happens. You are adding
> preferred_zone->node check. preferred_zone is the first zone in the
> requested zonelist. So for the most allocations it is a node from the
> local node. But if something request an explicit numa node (without
> __GFP_OTHER_NODE which would be the majority I suspect) then we could
> indeed end up accounting that as a NUMA_MISS, NUMA_FOREIGN so the
> referenced patch indeed caused an unintended change of accounting AFAIU.
>
This is a similar concern to what I had. If the preferred zone, which is
the first valid usable zone, is not a "hit" for the statistics then I
don't know what "hit" is meant to mean.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2016-12-20 13:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-12 5:59 [PATCH RFC 0/1] mm, page_alloc: fix incorrect zone_statistics data Jia He
2016-12-12 5:59 ` [PATCH RFC 1/1] " Jia He
2016-12-20 9:18 ` Michal Hocko
2016-12-20 13:10 ` Mel Gorman [this message]
2016-12-20 13:26 ` Michal Hocko
2016-12-20 14:28 ` Mel Gorman
2016-12-20 14:35 ` Michal Hocko
2016-12-20 14:49 ` Vlastimil Babka
2016-12-20 14:54 ` Mel Gorman
2016-12-21 7:57 ` Michal Hocko
2016-12-20 14:42 ` Mel Gorman
2016-12-20 15:13 ` Vlastimil Babka
2016-12-21 3:01 ` hejianet
2016-12-20 12:31 ` Mel Gorman
2016-12-21 3:07 ` hejianet
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