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From: Vlastimil Babka <vbabka@suse.cz>
To: bharata@linux.ibm.com
Cc: Christoph Lameter <cl@linux.com>, Will Deacon <will@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	guro@fb.com, Shakeel Butt <shakeelb@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	aneesh.kumar@linux.ibm.com, Jann Horn <jannh@google.com>,
	Michal Hocko <mhocko@kernel.org>,
	Catalin Marinas <Catalin.Marinas@arm.com>
Subject: Re: [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order
Date: Thu, 4 Feb 2021 10:33:47 +0100	[thread overview]
Message-ID: <aac07668-99a0-4c7e-5f8b-10751af364c5@suse.cz> (raw)
In-Reply-To: <20210203111009.GB2869122@in.ibm.com>

On 2/3/21 12:10 PM, Bharata B Rao wrote:
> On Wed, Jan 27, 2021 at 12:04:01PM +0100, Vlastimil Babka wrote:
>> Yes, but it's tricky to do the retuning safely, e.g. if freelist randomization
>> is enabled, see [1].
>> 
>> But as a quick fix for the regression, the heuristic idea could work reasonably
>> on all architectures?
>> - if num_present_cpus() is > 1, trust that it doesn't have the issue such as
>> arm64, and use it
>> - otherwise use nr_cpu_ids
>> 
>> Long-term we can attempt to do the retuning safe, or decide that number of cpus
>> shouldn't determine the order...
>> 
>> [1] https://lore.kernel.org/linux-mm/d7fb9425-9a62-c7b8-604d-5828d7e6b1da@suse.cz/
> 
> So what is preferrable here now? Above or other quick fix or reverting
> the original commit?

I would try the above first. In case it doesn't work, revert. As the immediate
fix for the regression, that people can safely backport.
Anything more complex will take more time and would be more risky to backport.

> Regards,
> Bharata.
> 


  parent reply	other threads:[~2021-02-04  9:34 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-18  8:27 [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order Bharata B Rao
2020-11-18 11:25 ` Vlastimil Babka
2020-11-18 19:34   ` Roman Gushchin
2020-11-18 19:53     ` David Rientjes
2021-01-20 17:36 ` Vincent Guittot
2021-01-21  5:30   ` Bharata B Rao
2021-01-21  9:09     ` Vincent Guittot
2021-01-21 10:01     ` Christoph Lameter
2021-01-21 10:48       ` Vincent Guittot
2021-01-21 18:19       ` Vlastimil Babka
2021-01-22  8:03         ` Vincent Guittot
2021-01-22 12:03           ` Vlastimil Babka
2021-01-22 13:16             ` Vincent Guittot
2021-01-23  5:16             ` Bharata B Rao
2021-01-23 12:32               ` Vincent Guittot
2021-01-25 11:20                 ` Vlastimil Babka
2021-01-26 23:03                   ` Will Deacon
2021-01-27  9:10                     ` Christoph Lameter
2021-01-27 11:04                       ` Vlastimil Babka
2021-02-03 11:10                         ` Bharata B Rao
2021-02-04  7:32                           ` Vincent Guittot
2021-02-04  9:07                             ` Christoph Lameter
2021-02-04  9:33                           ` Vlastimil Babka [this message]
2021-02-08 13:41                             ` [PATCH] mm, slub: better heuristic for number of cpus when calculating slab order Vlastimil Babka
2021-02-08 14:54                               ` Vincent Guittot
2021-02-10 14:07                               ` Mel Gorman
2021-01-22 13:05         ` [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order Jann Horn
2021-01-22 13:09           ` Jann Horn
2021-01-22 15:27           ` Vlastimil Babka
2021-01-25  4:28           ` Bharata B Rao
2021-01-26  8:52         ` Michal Hocko
2021-01-26 13:38           ` Vincent Guittot
2021-01-26 13:59             ` Michal Hocko
2021-01-27 13:38               ` Vlastimil Babka
2021-01-28 13:45               ` Mel Gorman
2021-01-28 13:57                 ` Michal Hocko
2021-01-28 14:42                   ` Mel Gorman

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