From: David Hildenbrand <david@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-kernel@vger.kernel.org, mhocko@suse.com,
linux-mm@kvack.org, osalvador@suse.de, richard.weiyang@gmail.com,
vbabka@suse.cz, rientjes@google.com
Subject: Re: [PATCH v2] mm/memory_hotplug: drain per-cpu pages again during memory offline
Date: Thu, 3 Sep 2020 21:35:35 +0200 [thread overview]
Message-ID: <C6941572-4380-4E07-A622-1BB63AE30622@redhat.com> (raw)
In-Reply-To: <20200903123136.1fa50e773eb58c6200801e65@linux-foundation.org>
> Am 03.09.2020 um 21:31 schrieb Andrew Morton <akpm@linux-foundation.org>:
>
> On Thu, 3 Sep 2020 19:36:26 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>> (still on vacation, back next week on Tuesday)
>>
>> I didn't look into discussions in v1, but to me this looks like we are
>> trying to hide an actual bug by implementing hacks in the caller
>> (repeated calls to drain_all_pages()). What about alloc_contig_range()
>> users - you get more allocation errors just because PCP code doesn't
>> play along.
>>
>> There *is* strong synchronization with the page allocator - however,
>> there seems to be one corner case race where we allow to allocate pages
>> from isolated pageblocks.
>>
>> I want that fixed instead if possible, otherwise this is just an ugly
>> hack to make the obvious symptoms (offlining looping forever) disappear.
>>
>> If that is not possible easily, I'd much rather want to see all
>> drain_all_pages() calls being moved to the caller and have the expected
>> behavior documented instead of specifying "there is no strong
>> synchronization with the page allocator" - which is wrong in all but PCP
>> cases (and there only in one possible race?).
>>
>
> It's a two-line hack which fixes a bug in -stable kernels, so I'm
> inclined to proceed with it anyway. We can undo it later on as part of
> a better fix, OK?
Agreed as a stable fix, but I really want to see a proper fix (e.g., disabling PCP while having isolated pageblocks) on top.
>
> Unless you think there's some new misbehaviour which we might see as a
> result of this approach?
>
We basically disable PCP by keeping to flush it. But performance shouldn‘t matter.
next prev parent reply other threads:[~2020-09-03 19:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 14:00 [PATCH v2] mm/memory_hotplug: drain per-cpu pages again during memory offline Pavel Tatashin
2020-09-03 17:36 ` David Hildenbrand
2020-09-03 18:07 ` Pavel Tatashin
2020-09-03 19:31 ` Andrew Morton
2020-09-03 19:35 ` David Hildenbrand [this message]
2020-09-04 12:42 ` Michal Hocko
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