From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
virtualization@lists.linux-foundation.org,
Tyler Sanderson <tysand@google.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
Wei Wang <wei.w.wang@intel.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Nadav Amit <namit@vmware.com>
Subject: Re: [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM
Date: Fri, 14 Feb 2020 15:18:55 +0100 [thread overview]
Message-ID: <802f93b1-1588-bd2c-8238-c12ec7f7ae9e@redhat.com> (raw)
In-Reply-To: <20200214140641.GB31689@dhcp22.suse.cz>
>> There was a report that this results in undesired side effects when
>> inflating the balloon to shrink the page cache. [1]
>> "When inflating the balloon against page cache (i.e. no free memory
>> remains) vmscan.c will both shrink page cache, but also invoke the
>> shrinkers -- including the balloon's shrinker. So the balloon
>> driver allocates memory which requires reclaim, vmscan gets this
>> memory by shrinking the balloon, and then the driver adds the
>> memory back to the balloon. Basically a busy no-op."
>>
>> The name "deflate on OOM" makes it pretty clear when deflation should
>> happen - after other approaches to reclaim memory failed, not while
>> reclaiming. This allows to minimize the footprint of a guest - memory
>> will only be taken out of the balloon when really needed.
>>
>> Especially, a drop_slab() will result in the whole balloon getting
>> deflated - undesired.
>
> Could you explain why some more? drop_caches shouldn't be really used in
> any production workloads and if somebody really wants all the cache to
> be dropped then why is balloon any different?
>
Deflation should happen when the guest is out of memory, not when
somebody thinks it's time to reclaim some memory. That's what the
feature promised from the beginning: Only give the guest more memory in
case it *really* needs more memory.
Deflate on oom, not deflate on reclaim/memory pressure. (that's what the
report was all about)
A priority for shrinkers might be a step into the right direction.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-02-14 14:19 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 16:33 [PATCH v1 0/3] virtio-balloon: Fixes + switch back to OOM handler David Hildenbrand
2020-02-05 16:34 ` [PATCH v1 1/3] virtio-balloon: Fix memory leak when unloading while hinting is in progress David Hildenbrand
2020-02-06 8:36 ` Michael S. Tsirkin
2020-02-05 16:34 ` [PATCH v1 2/3] virtio_balloon: Fix memory leaks on errors in virtballoon_probe() David Hildenbrand
2020-02-06 8:36 ` Michael S. Tsirkin
2020-02-05 16:34 ` [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM David Hildenbrand
2020-02-05 22:37 ` Tyler Sanderson
2020-02-05 22:52 ` David Hildenbrand
2020-02-05 23:06 ` Tyler Sanderson
2020-02-06 7:40 ` Michael S. Tsirkin
2020-02-06 8:42 ` David Hildenbrand
2020-02-06 8:57 ` Michael S. Tsirkin
2020-02-06 9:05 ` David Hildenbrand
2020-02-06 9:09 ` Michael S. Tsirkin
2020-02-06 8:57 ` Wang, Wei W
2020-02-06 9:11 ` Michael S. Tsirkin
2020-02-06 9:12 ` Michael S. Tsirkin
2020-02-06 9:21 ` David Hildenbrand
2020-02-14 9:51 ` David Hildenbrand
2020-02-14 13:31 ` Wang, Wei W
2020-02-16 9:47 ` Michael S. Tsirkin
2020-02-21 3:29 ` Tyler Sanderson
2020-03-08 4:47 ` Tyler Sanderson
2020-03-09 9:03 ` David Hildenbrand
2020-03-09 10:14 ` Michael S. Tsirkin
2020-03-09 10:59 ` David Hildenbrand
2020-03-09 10:24 ` Michael S. Tsirkin
2020-02-14 14:06 ` Michal Hocko
2020-02-14 14:18 ` David Hildenbrand [this message]
2020-02-14 20:48 ` Tyler Sanderson
2020-02-14 21:17 ` David Hildenbrand
2020-02-16 9:46 ` Michael S. Tsirkin
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