From: Bharata B Rao <bharata@linux.ibm.com>
To: Vlastimil Babka <vbabka@suse.cz>
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: Wed, 3 Feb 2021 16:40:09 +0530 [thread overview]
Message-ID: <20210203111009.GB2869122@in.ibm.com> (raw)
In-Reply-To: <81424d71-c479-4c4a-de14-0a9b3f636e23@suse.cz>
On Wed, Jan 27, 2021 at 12:04:01PM +0100, Vlastimil Babka wrote:
> On 1/27/21 10:10 AM, Christoph Lameter wrote:
> > On Tue, 26 Jan 2021, Will Deacon wrote:
> >
> >> > Hm, but booting the secondaries is just a software (kernel) action? They are
> >> > already physically there, so it seems to me as if the cpu_present_mask is not
> >> > populated correctly on arm64, and it's just a mirror of cpu_online_mask?
> >>
> >> I think the present_mask retains CPUs if they are hotplugged off, whereas
> >> the online mask does not. We can't really do any better on arm64, as there's
> >> no way of telling that a CPU is present until we've seen it.
> >
> > The order of each page in a kmem cache --and therefore also the number
> > of objects in a slab page-- can be different because that information is
> > stored in the page struct.
> >
> > Therefore it is possible to retune the order while the cache is in operaton.
>
> 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?
Regards,
Bharata.
next prev parent reply other threads:[~2021-02-03 11:11 UTC|newest]
Thread overview: 52+ 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
2020-11-18 19:53 ` David Rientjes
2021-01-20 17:36 ` Vincent Guittot
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 9:09 ` Vincent Guittot
2021-01-21 10:01 ` Christoph Lameter
2021-01-21 10:01 ` Christoph Lameter
2021-01-21 10:48 ` Vincent Guittot
2021-01-21 10:48 ` Vincent Guittot
2021-01-21 18:19 ` Vlastimil Babka
2021-01-22 8:03 ` Vincent Guittot
2021-01-22 8:03 ` Vincent Guittot
2021-01-22 12:03 ` Vlastimil Babka
2021-01-22 13:16 ` Vincent Guittot
2021-01-22 13:16 ` Vincent Guittot
2021-01-23 5:16 ` Bharata B Rao
2021-01-23 12:32 ` Vincent Guittot
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 9:10 ` Christoph Lameter
2021-01-27 11:04 ` Vlastimil Babka
2021-02-03 11:10 ` Bharata B Rao [this message]
2021-02-04 7:32 ` Vincent Guittot
2021-02-04 7:32 ` Vincent Guittot
2021-02-04 9:07 ` Christoph Lameter
2021-02-04 9:07 ` Christoph Lameter
2021-02-04 9:33 ` Vlastimil Babka
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
2021-02-08 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 13:05 ` Jann Horn
2021-01-22 13:09 ` 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 13:38 ` 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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