From: Baoquan He <bhe@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
mhocko@suse.com, akpm@linux-foundation.org, aarcange@redhat.com
Subject: Re: Memory hotplug softlock issue
Date: Wed, 14 Nov 2018 17:00:42 +0800 [thread overview]
Message-ID: <20181114090042.GD2653@MiWiFi-R3L-srv> (raw)
In-Reply-To: <5a6c6d6b-ebcd-8bfa-d6e0-4312bfe86586@redhat.com>
Hi David,
On 11/14/18 at 09:18am, David Hildenbrand wrote:
> Code seems to be waiting for the mem_hotplug_lock in read.
> We hold mem_hotplug_lock in write whenever we online/offline/add/remove
> memory. There are two ways to trigger offlining of memory:
>
> 1. Offlining via "cat offline > /sys/devices/system/memory/memory0/state"
>
> This always properly took the mem_hotplug_lock. Nothing changed
>
> 2. Offlining via "cat 0 > /sys/devices/system/memory/memory0/online"
>
> This didn't take the mem_hotplug_lock and I fixed that for this release.
>
> So if you were testing with 1., you should have seen the same error
> before this release (unless there is something else now broken in this
> release).
Thanks a lot for looking into this.
I triggered sysrq+t to check threads' state. You can see that we use
firmware to trigger ACPI event to go to acpi_bus_offline(), it truly
didn't take mem_hotplug_lock() and has taken it with your fix in
commit 381eab4a6ee mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
[ +0.007062] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
[ +0.005398] Call Trace:
[ +0.002476] ? page_vma_mapped_walk+0x307/0x710
[ +0.004538] ? page_remove_rmap+0xa2/0x340
[ +0.004104] ? ptep_clear_flush+0x54/0x60
[ +0.004027] ? enqueue_entity+0x11c/0x620
[ +0.005904] ? schedule+0x28/0x80
[ +0.003336] ? rmap_walk_file+0xf9/0x270
[ +0.003940] ? try_to_unmap+0x9c/0xf0
[ +0.003695] ? migrate_pages+0x2b0/0xb90
[ +0.003959] ? try_offline_node+0x160/0x160
[ +0.004214] ? __offline_pages+0x6ce/0x8e0
[ +0.004134] ? memory_subsys_offline+0x40/0x60
[ +0.004474] ? device_offline+0x81/0xb0
[ +0.003867] ? acpi_bus_offline+0xdb/0x140
[ +0.004117] ? acpi_device_hotplug+0x21c/0x460
[ +0.004458] ? acpi_hotplug_work_fn+0x1a/0x30
[ +0.004372] ? process_one_work+0x1a1/0x3a0
[ +0.004195] ? worker_thread+0x30/0x380
[ +0.003851] ? drain_workqueue+0x120/0x120
[ +0.004117] ? kthread+0x112/0x130
[ +0.003411] ? kthread_park+0x80/0x80
[ +0.005325] ? ret_from_fork+0x35/0x40
>
>
> The real question is, however, why offlining of the last block doesn't
> succeed. In __offline_pages() we basically have an endless loop (while
> holding the mem_hotplug_lock in write). Now I consider this piece of
> code very problematic (we should automatically fail after X
> attempts/after X seconds, we should not ignore -ENOMEM), and we've had
> other BUGs whereby we would run into an endless loop here (e.g. related
> to hugepages I guess).
Hmm, even though memory hotplug stalled there, there are still much
memory. E.g in this system, it has 8 nodes and each node has 64 GB
memory, it's 512 GB in all. Now I run "stress -m 200" to trigger 200
processes to malloc then free 256 MB contiously, and it's eating 50 GB
in all. In theory, it still has much memory for migrating to.
>
> You mentioned memory pressure, if our host is under memory pressure we
> can easily trigger running into an endless loop there, because we
> basically ignore -ENOMEM e.g. when we cannot get a page to migrate some
> memory to be offlined. I assume this is the case here.
> do_migrate_range() could be the bad boy if it keeps failing forever and
> we keep retrying.
Not sure what other people think about this. If failed the memory removing
when still much free memory left, I worry customer will complain.
Yeah, it stoped at do_migrate_range() when try to migrate the last
memory block. And each time it's the last memory block which can't be
offlined and hang.
If any message or information needed, I can provide.
Thanks
Baoquan
next prev parent reply other threads:[~2018-11-14 9:01 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 7:09 Memory hotplug softlock issue Baoquan He
2018-11-14 7:16 ` Baoquan He
2018-11-14 8:18 ` David Hildenbrand
2018-11-14 9:00 ` Baoquan He [this message]
2018-11-14 9:25 ` David Hildenbrand
2018-11-14 9:41 ` Michal Hocko
2018-11-14 9:48 ` David Hildenbrand
2018-11-14 10:04 ` Michal Hocko
2018-11-14 9:01 ` Michal Hocko
2018-11-14 9:22 ` David Hildenbrand
2018-11-14 9:37 ` Michal Hocko
2018-11-14 9:39 ` David Hildenbrand
2018-11-14 14:52 ` Baoquan He
2018-11-14 15:00 ` Michal Hocko
2018-11-15 5:10 ` Baoquan He
2018-11-15 7:30 ` Michal Hocko
2018-11-15 7:53 ` Baoquan He
2018-11-15 8:30 ` Michal Hocko
2018-11-15 9:42 ` David Hildenbrand
2018-11-15 9:52 ` Baoquan He
2018-11-15 9:53 ` David Hildenbrand
2018-11-15 13:12 ` Baoquan He
2018-11-15 13:19 ` Michal Hocko
2018-11-15 13:23 ` Baoquan He
2018-11-15 14:25 ` Michal Hocko
2018-11-15 13:38 ` Baoquan He
2018-11-15 14:32 ` Michal Hocko
2018-11-15 14:34 ` Baoquan He
2018-11-16 1:24 ` Baoquan He
2018-11-16 9:14 ` Michal Hocko
2018-11-17 4:22 ` Baoquan He
[not found] ` <20181119105202.GE18471@MiWiFi-R3L-srv>
2018-11-19 12:40 ` Michal Hocko
2018-11-19 12:51 ` Michal Hocko
2018-11-19 14:10 ` Michal Hocko
2018-11-19 16:36 ` Vlastimil Babka
2018-11-19 16:46 ` Michal Hocko
2018-11-19 16:46 ` Vlastimil Babka
2018-11-19 16:48 ` Vlastimil Babka
2018-11-19 17:01 ` Michal Hocko
2018-11-19 17:33 ` Michal Hocko
2018-11-19 20:34 ` Hugh Dickins
2018-11-19 20:59 ` Michal Hocko
2018-11-20 1:56 ` Baoquan He
2018-11-20 5:44 ` Hugh Dickins
2018-11-20 13:38 ` Vlastimil Babka
2018-11-20 13:58 ` Baoquan He
2018-11-20 14:05 ` Michal Hocko
2018-11-20 14:12 ` Baoquan He
2018-11-21 1:21 ` Hugh Dickins
2018-11-21 1:08 ` Hugh Dickins
2018-11-21 3:20 ` Hugh Dickins
2018-11-21 17:31 ` Michal Hocko
2018-11-22 1:53 ` Hugh Dickins
2018-11-14 10:00 ` Michal Hocko
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