From: Christoph Lameter <cl@linux.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Bharata B Rao <bharata@linux.ibm.com>,
Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.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 09:07:27 +0000 (UTC) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2102040851170.76039@www.lameter.com> (raw)
In-Reply-To: <CAKfTPtBLnig+M0pjoYEYtDbVLT=J5fkn9__RrsiTrUB_51XcZw@mail.gmail.com>
On Thu, 4 Feb 2021, Vincent Guittot wrote:
> > So what is preferrable here now? Above or other quick fix or reverting
> > the original commit?
>
> I'm fine with whatever the solution as long as we can use keep using
> nr_cpu_ids when other values like num_present_cpus, don't reflect
> correctly the system
AFAICT they are correctly reflecting the current state of the system.
The problem here is the bringup of the system and the tuning therefor.
One additional thing that may help: The slab caches can work in a degraded
mode where no fastpath allocations can occur. That mode is used primarily
for debugging but maybe that mode can also help during bootstrap to avoid
having to deal with the per cpu data and so on.
In degraded mode SLUB will take a lock for each operation on an object.
In this mode the following is true
kmem_cache_cpu->page == NULL
kmem_cache_cpu->freelist == NULL
kmem_cache_debug(s) == true
So if you define a new debug mode and include it in SLAB_DEBUG_FLAGS then
you can force SLUB to fallback to operations where a lock is taken and
where slab allocation can be stopped. This may be ok for bring up.
The debug flags are also tied to some wizardry that can patch the code at
runtime to optimize for debubgging or fast operations. You would tie into
that one as well. Start in debug mode by default and switch to fast
operations after all processors are up.
next prev parent reply other threads:[~2021-02-04 9:11 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
2021-02-04 7:32 ` Vincent Guittot
2021-02-04 7:32 ` Vincent Guittot
2021-02-04 9:07 ` Christoph Lameter [this message]
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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