From: David Hildenbrand <david@redhat.com>
To: Mike Kravetz <mike.kravetz@oracle.com>, linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>,
"Michael S.Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate()
Date: Wed, 29 Jul 2020 20:08:56 +0200 [thread overview]
Message-ID: <7d32cdd3-7f19-2916-1930-33236bf33e19@redhat.com> (raw)
In-Reply-To: <6a05470a-75be-e895-dff6-ed494af8d6d9@oracle.com>
On 29.07.20 19:31, Mike Kravetz wrote:
> On 6/30/20 7:26 AM, David Hildenbrand wrote:
>> Right now, if we have two isolations racing, we might trigger the
>> WARN_ON_ONCE() and to dump_page(NULL), dereferencing NULL. Let's just
>> return directly.
>
> Just curious, what call path has the WARN_ON_ONCE()/dump_page(NULL)?
See below, two set_migratetype_isolate() caller racing.
>
>>
>> In the future, we might want to report -EAGAIN to the caller instead, as
>> this could indicate a temporary isolation failure only.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>
> Hi David,
>
> That 'return -EAGAIN' was added as a sort of synchronization mechanism.
> See commit message for 2c7452a075d4d. Before adding the 'return -EAGAIN',
> I could create races which would abandon isolated pageblocks. Repeating
> those races over and over would result in a good chunk of system memory
> being isolated and unusable.
It's actually -EBUSY, it should maybe later be changed to -EAGAIN (see
comment), so caller can decide to retry immediately. Other discussion.
>
> Admittedly, these races are rare and I had to work really hard to produce
> them. I'll try to find my testing mechanism. My concern is reintroducing
> this abandoning of pageblocks. I have not looked further in your series
> to see if this potentially addressed later. If not, then we should not
> remove the return code.
>
Memory offlining could race with alloc_contig_range(), e.g., called when
allocating gigantic pages, or when virtio-mem tries to unplug memory.
The latter two could also race.
We are getting more alloc_contig_range() users, which is why these races
will become more relevant.
I have no clue what you mean with "reintroducing this abandoning of
pageblocks". All this patch is changing is not doing the dump_page() -
or am I missing something important?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-07-29 18:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-30 14:26 [PATCH v1 0/6] mm / virtio-mem: support ZONE_MOVABLE David Hildenbrand
2020-06-30 14:26 ` [PATCH v1 1/6] mm/page_alloc: tweak comments in has_unmovable_pages() David Hildenbrand
2020-07-28 13:48 ` Baoquan He
2020-07-28 14:07 ` David Hildenbrand
2020-07-29 10:47 ` Baoquan He
2020-07-29 12:29 ` David Hildenbrand
2020-06-30 14:26 ` [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate() David Hildenbrand
2020-07-28 13:56 ` Baoquan He
2020-07-29 17:31 ` Mike Kravetz
2020-07-29 18:08 ` David Hildenbrand [this message]
2020-07-29 18:35 ` Mike Kravetz
2020-07-29 18:41 ` David Hildenbrand
2020-07-30 4:21 ` Pankaj Gupta
2020-06-30 14:26 ` [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() " David Hildenbrand
2020-07-29 13:24 ` Baoquan He
2020-07-29 13:37 ` David Hildenbrand
2020-07-29 14:05 ` Baoquan He
2020-06-30 14:26 ` [PATCH v1 4/6] mm/page_isolation: cleanup set_migratetype_isolate() David Hildenbrand
2020-07-29 14:06 ` Baoquan He
2020-07-30 4:31 ` Pankaj Gupta
2020-06-30 14:26 ` [PATCH v1 5/6] mm/page_alloc: restrict ZONE_MOVABLE optimization in has_unmovable_pages() to memory offlining David Hildenbrand
2020-07-27 12:23 ` David Hildenbrand
2020-06-30 14:26 ` [PATCH v1 6/6] virtio-mem: don't special-case ZONE_MOVABLE David Hildenbrand
2020-07-21 9:59 ` [PATCH v1 0/6] mm / virtio-mem: support ZONE_MOVABLE David Hildenbrand
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