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From: David Hildenbrand <david@redhat.com>
To: Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, Michal Hocko <mhocko@kernel.org>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Oscar Salvador <osalvador@suse.de>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH 0/9] disable pcplists during memory offline
Date: Tue, 22 Sep 2020 19:15:58 +0200	[thread overview]
Message-ID: <bc582c01-7904-cb09-0f95-b170cb33c958@redhat.com> (raw)
In-Reply-To: <20200922143712.12048-1-vbabka@suse.cz>

On 22.09.20 16:37, Vlastimil Babka wrote:
> As per the discussions [1] [2] this is an attempt to implement David's
> suggestion that page isolation should disable pcplists to avoid races with page
> freeing in progress. This is done without extra checks in fast paths, as
> explained in Patch 9. The repeated draining done by [2] is then no longer
> needed. Previous version (RFC) is at [3].
> 
> The RFC tried to hide pcplists disabling/enabling into page isolation, but it
> wasn't completely possible, as memory offline does not unisolation. Michal
> suggested an explicit API in [4] so that's the current implementation and it
> seems indeed nicer.
> 
> Once we accept that page isolation users need to do explicit actions around it
> depending on the needed guarantees, we can also IMHO accept that the current
> pcplist draining can be also done by the callers, which is more effective.
> After all, there are only two users of page isolation. So patch 7 does
> effectively the same thing as Pavel proposed in [5], and patches 8-9 implement
> stronger guarantees only for memory offline. If CMA decides to opt-in to the
> stronger guarantee, it's easy to do so.
> 
> Patches 1-6 are preparatory cleanups for pcplist disabling.
> 
> Patchset was briefly tested in QEMU so that memory online/offline works, but
> I haven't done a stress test that would prove the race fixed by [2] is
> eliminated.
> 
> Note that patch 9 could be avoided if we instead adjusted page freeing in shown
> in [6], but I believe the current implementation of disabling pcplists is not
> too much complex, so I would prefer this instead of adding new checks and
> longer irq-disabled section into page freeing hotpaths.

Haven't looked into the details (yet), but I assume we can add some flag
to alloc_contig_range(), to also disable+flush+enable. (or let the
caller do it, for example on a bunch of bulk allocations - TBD).

Result of patch #9 looks quite clean.

-- 
Thanks,

David / dhildenb


      parent reply	other threads:[~2020-09-22 17:16 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-22 14:37 [PATCH 0/9] disable pcplists during memory offline Vlastimil Babka
2020-09-22 14:37 ` [PATCH 1/9] mm, page_alloc: clean up pageset high and batch update Vlastimil Babka
2020-09-25 10:18   ` David Hildenbrand
2020-10-05 12:03   ` Michal Hocko
2020-09-22 14:37 ` [PATCH 2/9] mm, page_alloc: calculate pageset high and batch once per zone Vlastimil Babka
2020-10-05 12:52   ` Michal Hocko
2020-10-06 22:04     ` Vlastimil Babka
2020-09-22 14:37 ` [PATCH 3/9] mm, page_alloc: remove setup_pageset() Vlastimil Babka
2020-09-25 10:19   ` David Hildenbrand
2020-10-05 12:59   ` Michal Hocko
2020-10-06 22:11     ` Vlastimil Babka
2020-09-22 14:37 ` [PATCH 4/9] mm, page_alloc: simplify pageset_update() Vlastimil Babka
2020-09-25 10:23   ` David Hildenbrand
2020-10-05 13:20   ` Michal Hocko
2020-09-22 14:37 ` [PATCH 5/9] mm, page_alloc: make per_cpu_pageset accessible only after init Vlastimil Babka
2020-09-25 10:25   ` David Hildenbrand
2020-10-05 13:24   ` Michal Hocko
2020-10-06 22:28     ` Vlastimil Babka
2020-09-22 14:37 ` [PATCH 6/9] mm, page_alloc: cache pageset high and batch in struct zone Vlastimil Babka
2020-09-25 10:34   ` David Hildenbrand
2020-10-06 22:31     ` Vlastimil Babka
2020-10-05 13:28   ` Michal Hocko
2020-10-06 22:34     ` Vlastimil Babka
2020-09-22 14:37 ` [PATCH 7/9] mm, page_alloc: move draining pcplists to page isolation users Vlastimil Babka
2020-09-25 10:39   ` David Hildenbrand
2020-10-05 13:57   ` Michal Hocko
2020-09-22 14:37 ` [PATCH 8/9] mm, page_alloc: drain all pcplists during memory offline Vlastimil Babka
2020-09-25 10:46   ` David Hildenbrand
2020-10-05 14:03     ` Michal Hocko
2020-09-22 14:37 ` [PATCH 9/9] mm, page_alloc: optionally disable pcplists during page isolation Vlastimil Babka
2020-09-25 10:53   ` David Hildenbrand
2020-09-25 10:54     ` David Hildenbrand
2020-09-25 11:10       ` Vlastimil Babka
2020-10-01  8:47         ` David Hildenbrand
2020-10-05 14:05         ` Michal Hocko
2020-10-05 14:22           ` Vlastimil Babka
2020-10-05 16:56             ` Michal Hocko
2020-10-06  8:34   ` Michal Hocko
2020-10-06  8:40     ` David Hildenbrand
2020-10-06 10:05       ` Michal Hocko
2020-09-22 17:15 ` David Hildenbrand [this message]

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