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From: Mel Gorman <mgorman@techsingularity.net>
To: Jia He <hejianet@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>, Michal Hocko <mhocko@suse.com>,
	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 12:31:22 +0000	[thread overview]
Message-ID: <20161220123121.e4wgkxm2txdoxogo@techsingularity.net> (raw)
In-Reply-To: <1481522347-20393-2-git-send-email-hejianet@gmail.com>

On Mon, Dec 12, 2016 at 01:59:07PM +0800, 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.
> 
> Fixes: commit b9f00e147f27 ("mm, page_alloc: reduce branches in
> zone_statistics")
> 
> Signed-off-by: Jia He <hejianet@gmail.com>

This is slightly curious. It appear it would only occur if a process was
running on a node that was outside the memory policy. Can you confirm
that is the case?

If so, your patch is a a semantic curiousity because it's actually
impossible for a NUMA allocation to be local and the definition of "HIT"
is fuzzy enough to be useless.

I won't object to the patch but it makes me trust "hit" even less than I
already do for any analysis.

Note that after this mail that I'll be unavailable by mail until early
new years.

-- 
Mel Gorman
SUSE Labs

WARNING: multiple messages have this Message-ID
From: Mel Gorman <mgorman@techsingularity.net>
To: Jia He <hejianet@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>, Michal Hocko <mhocko@suse.com>,
	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 12:31:22 +0000	[thread overview]
Message-ID: <20161220123121.e4wgkxm2txdoxogo@techsingularity.net> (raw)
In-Reply-To: <1481522347-20393-2-git-send-email-hejianet@gmail.com>

On Mon, Dec 12, 2016 at 01:59:07PM +0800, 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.
> 
> Fixes: commit b9f00e147f27 ("mm, page_alloc: reduce branches in
> zone_statistics")
> 
> Signed-off-by: Jia He <hejianet@gmail.com>

This is slightly curious. It appear it would only occur if a process was
running on a node that was outside the memory policy. Can you confirm
that is the case?

If so, your patch is a a semantic curiousity because it's actually
impossible for a NUMA allocation to be local and the definition of "HIT"
is fuzzy enough to be useless.

I won't object to the patch but it makes me trust "hit" even less than I
already do for any analysis.

Note that after this mail that I'll be unavailable by mail until early
new years.

-- 
Mel Gorman
SUSE Labs

--
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  parent reply	other threads:[~2016-12-20 12:31 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-12  5:59 [PATCH RFC 0/1] " Jia He
2016-12-12  5:59 ` Jia He
2016-12-12  5:59 ` [PATCH RFC 1/1] " Jia He
2016-12-12  5:59   ` Jia He
2016-12-20  9:18   ` Michal Hocko
2016-12-20  9:18     ` Michal Hocko
2016-12-20 13:10     ` Mel Gorman
2016-12-20 13:10       ` Mel Gorman
2016-12-20 13:26       ` Michal Hocko
2016-12-20 13:26         ` Michal Hocko
2016-12-20 14:28         ` Mel Gorman
2016-12-20 14:28           ` Mel Gorman
2016-12-20 14:35           ` Michal Hocko
2016-12-20 14:35             ` Michal Hocko
2016-12-20 14:49             ` Vlastimil Babka
2016-12-20 14:49               ` Vlastimil Babka
2016-12-20 14:54             ` Mel Gorman
2016-12-20 14:54               ` Mel Gorman
2016-12-21  7:57               ` Michal Hocko
2016-12-21  7:57                 ` Michal Hocko
2016-12-21  8:06                 ` [PATCH 1/2] mm: fix remote numa hits statistics Michal Hocko
2016-12-21  8:06                   ` [PATCH 2/2] mm: get rid of __GFP_OTHER_NODE Michal Hocko
2017-01-02 14:18                     ` Vlastimil Babka
2016-12-29 11:46                   ` [PATCH 1/2] mm: fix remote numa hits statistics Mel Gorman
2016-12-29 12:28                     ` Michal Hocko
2017-01-02 14:16                   ` Vlastimil Babka
2017-01-02 14:46                     ` Michal Hocko
2017-01-02 15:07                       ` Vlastimil Babka
2016-12-20 14:42           ` [PATCH RFC 1/1] mm, page_alloc: fix incorrect zone_statistics data Mel Gorman
2016-12-20 14:42             ` Mel Gorman
2016-12-20 15:13     ` Vlastimil Babka
2016-12-20 15:13       ` Vlastimil Babka
2016-12-21  3:01     ` hejianet
2016-12-21  3:01       ` hejianet
2016-12-20 12:31   ` Mel Gorman [this message]
2016-12-20 12:31     ` Mel Gorman
2016-12-21  3:07     ` hejianet
2016-12-21  3:07       ` hejianet

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