From: "Michael S. Tsirkin" <mst@redhat.com>
To: Tyler Sanderson <tysand@google.com>
Cc: "virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
namit@vmware.com, David Rientjes <rientjes@google.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Michal Hocko <mhocko@kernel.org>
Subject: Re: Balloon pressuring page cache
Date: Tue, 4 Feb 2020 13:56:21 -0500 [thread overview]
Message-ID: <20200204135533-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CAJuQAmpiVqnNt-vSkQh5Gg63QZ49_nuz4+VW2Jfwn51gWVdtfA@mail.gmail.com>
On Tue, Feb 04, 2020 at 10:52:42AM -0800, Tyler Sanderson wrote:
>
>
> On Tue, Feb 4, 2020 at 12:29 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 03.02.20 21:32, Tyler Sanderson wrote:
> > There were apparently good reasons for moving away from OOM notifier
> > callback:
> > https://lkml.org/lkml/2018/7/12/314
> > https://lkml.org/lkml/2018/8/2/322
> >
> > In particular the OOM notifier is worse than the shrinker because:
>
> The issue is that DEFLATE_ON_OOM is under-specified.
>
> >
> >Â 1. It is last-resort, which means the system has already gone through
> >Â Â Â heroics to prevent OOM. Those heroic reclaim efforts are expensive
> >Â Â Â and impact application performance.
>
> That's *exactly* what "deflate on OOM" suggests.
>
>
> It seems there are some use cases where "deflate on OOM" is desired and others
> where "deflate on pressure" is desired.
> This suggests adding a new feature bit "DEFLATE_ON_PRESSURE" that registers the
> shrinker, and reverting DEFLATE_ON_OOM to use the OOM notifier callback.
>
> This lets users configure the balloon for their use case.
Right. Let's not repeat past mistakes and let's try to specify this
new one properly though :)
>
>
> Assume you are using virtio-balloon for some weird way of memory
> hotunplug (which is what some people do) and you want to minimize the
> footprint of your guest. Then you really only want to give the guest
> more memory (or rather, let it take back memory automatically in this
> case) in case it really needs more memory. It should try to reclaim first.
>
> Under-specified.
>
>
> >Â 2. It lacks understanding of NUMA or other OOM constraints.
>
> Ballooning in general lacks the understanding of NUMA.
>
> > 3. It has a higher potential for bugs due to the subtlety of the
> >Â Â Â callback context.
>
> While that is a valid point, it doesn't explain why existing
> functionality is changed.
>
> Personally, I think DEFLATE_ON_OOM should never have been introduced (at
> least not in this form).
>
> I'm actually not sure how you would safely do memory overcommit without
> DEFLATE_ON_OOM. So I think it unlocks a huge use case.
> Â
>
>
>
> --
> Thanks,
>
> David / dhildenb
>
>
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Tyler Sanderson <tysand@google.com>
Cc: David Hildenbrand <david@redhat.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
"Wang, Wei W" <wei.w.wang@intel.com>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
David Rientjes <rientjes@google.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Michal Hocko <mhocko@kernel.org>,
namit@vmware.com
Subject: Re: Balloon pressuring page cache
Date: Tue, 4 Feb 2020 13:56:21 -0500 [thread overview]
Message-ID: <20200204135533-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CAJuQAmpiVqnNt-vSkQh5Gg63QZ49_nuz4+VW2Jfwn51gWVdtfA@mail.gmail.com>
On Tue, Feb 04, 2020 at 10:52:42AM -0800, Tyler Sanderson wrote:
>
>
> On Tue, Feb 4, 2020 at 12:29 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 03.02.20 21:32, Tyler Sanderson wrote:
> > There were apparently good reasons for moving away from OOM notifier
> > callback:
> > https://lkml.org/lkml/2018/7/12/314
> > https://lkml.org/lkml/2018/8/2/322
> >
> > In particular the OOM notifier is worse than the shrinker because:
>
> The issue is that DEFLATE_ON_OOM is under-specified.
>
> >
> > 1. It is last-resort, which means the system has already gone through
> > heroics to prevent OOM. Those heroic reclaim efforts are expensive
> > and impact application performance.
>
> That's *exactly* what "deflate on OOM" suggests.
>
>
> It seems there are some use cases where "deflate on OOM" is desired and others
> where "deflate on pressure" is desired.
> This suggests adding a new feature bit "DEFLATE_ON_PRESSURE" that registers the
> shrinker, and reverting DEFLATE_ON_OOM to use the OOM notifier callback.
>
> This lets users configure the balloon for their use case.
Right. Let's not repeat past mistakes and let's try to specify this
new one properly though :)
>
>
> Assume you are using virtio-balloon for some weird way of memory
> hotunplug (which is what some people do) and you want to minimize the
> footprint of your guest. Then you really only want to give the guest
> more memory (or rather, let it take back memory automatically in this
> case) in case it really needs more memory. It should try to reclaim first.
>
> Under-specified.
>
>
> > 2. It lacks understanding of NUMA or other OOM constraints.
>
> Ballooning in general lacks the understanding of NUMA.
>
> > 3. It has a higher potential for bugs due to the subtlety of the
> > callback context.
>
> While that is a valid point, it doesn't explain why existing
> functionality is changed.
>
> Personally, I think DEFLATE_ON_OOM should never have been introduced (at
> least not in this form).
>
> I'm actually not sure how you would safely do memory overcommit without
> DEFLATE_ON_OOM. So I think it unlocks a huge use case.
>
>
>
>
> --
> Thanks,
>
> David / dhildenb
>
>
next prev parent reply other threads:[~2020-02-04 18:56 UTC|newest]
Thread overview: 119+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 0:22 Balloon pressuring page cache Tyler Sanderson via Virtualization
2020-01-29 10:31 ` David Hildenbrand
2020-01-29 19:11 ` Tyler Sanderson via Virtualization
2020-01-30 15:02 ` David Hildenbrand
2020-01-30 15:02 ` David Hildenbrand
2020-01-30 15:20 ` Michael S. Tsirkin
2020-01-30 15:20 ` Michael S. Tsirkin
2020-01-30 15:23 ` David Hildenbrand
2020-01-30 15:23 ` David Hildenbrand
2020-01-30 15:31 ` Wang, Wei W
2020-01-30 15:31 ` Wang, Wei W
2020-01-30 19:59 ` Tyler Sanderson via Virtualization
2020-01-30 19:59 ` Tyler Sanderson
2020-02-03 13:11 ` Michael S. Tsirkin
2020-02-03 13:11 ` Michael S. Tsirkin
2020-02-03 16:18 ` Alexander Duyck
2020-02-03 16:34 ` David Hildenbrand
2020-02-03 16:34 ` David Hildenbrand
2020-02-03 17:03 ` Michael S. Tsirkin
2020-02-03 17:03 ` Michael S. Tsirkin
2020-02-03 20:32 ` Tyler Sanderson via Virtualization
2020-02-03 20:32 ` Tyler Sanderson
2020-02-03 21:22 ` Alexander Duyck
2020-02-03 23:16 ` Tyler Sanderson via Virtualization
2020-02-03 23:16 ` Tyler Sanderson
2020-02-04 0:10 ` Alexander Duyck
2020-02-04 5:45 ` Michael S. Tsirkin
2020-02-04 5:45 ` Michael S. Tsirkin
2020-02-04 8:29 ` David Hildenbrand
2020-02-04 8:29 ` David Hildenbrand
2020-02-04 18:52 ` Tyler Sanderson via Virtualization
2020-02-04 18:52 ` Tyler Sanderson
2020-02-04 18:56 ` Michael S. Tsirkin [this message]
2020-02-04 18:56 ` Michael S. Tsirkin
2020-02-04 19:17 ` David Hildenbrand
2020-02-04 19:17 ` David Hildenbrand
2020-02-04 23:58 ` Tyler Sanderson via Virtualization
2020-02-04 23:58 ` Tyler Sanderson
2020-02-05 0:15 ` Tyler Sanderson via Virtualization
2020-02-05 0:15 ` Tyler Sanderson
2020-02-05 6:57 ` Michael S. Tsirkin
2020-02-05 6:57 ` Michael S. Tsirkin
2020-02-05 19:01 ` Tyler Sanderson via Virtualization
2020-02-05 19:01 ` Tyler Sanderson
2020-02-05 19:22 ` Alexander Duyck
2020-02-05 21:44 ` Tyler Sanderson via Virtualization
2020-02-05 21:44 ` Tyler Sanderson
2020-02-06 11:00 ` David Hildenbrand
2020-02-06 11:00 ` David Hildenbrand
2020-02-03 22:50 ` Nadav Amit via Virtualization
2020-02-03 22:50 ` Nadav Amit
2020-02-04 8:35 ` David Hildenbrand
2020-02-04 8:35 ` David Hildenbrand
2020-02-04 8:40 ` Michael S. Tsirkin
2020-02-04 8:40 ` Michael S. Tsirkin
2020-02-04 8:48 ` David Hildenbrand
2020-02-04 8:48 ` David Hildenbrand
2020-02-04 14:30 ` David Hildenbrand
2020-02-04 14:30 ` David Hildenbrand
2020-02-04 16:50 ` Michael S. Tsirkin
2020-02-04 16:50 ` Michael S. Tsirkin
2020-02-04 16:56 ` David Hildenbrand
2020-02-04 16:56 ` David Hildenbrand
2020-02-04 20:33 ` [virtio-dev] " Michael S. Tsirkin
2020-02-04 20:33 ` Michael S. Tsirkin
2020-02-04 20:33 ` Michael S. Tsirkin
2020-02-05 8:31 ` [virtio-dev] " David Hildenbrand
2020-02-05 8:31 ` David Hildenbrand
2020-02-05 6:52 ` Wang, Wei W
2020-02-05 6:52 ` Wang, Wei W
2020-02-05 7:05 ` Michael S. Tsirkin
2020-02-05 7:05 ` Michael S. Tsirkin
2020-02-05 8:50 ` Wang, Wei W
2020-02-05 8:50 ` Wang, Wei W
2020-02-05 6:49 ` Wang, Wei W
2020-02-05 6:49 ` Wang, Wei W
2020-02-05 8:19 ` David Hildenbrand
2020-02-05 8:19 ` David Hildenbrand
2020-02-05 8:54 ` Wang, Wei W
2020-02-05 8:54 ` Wang, Wei W
2020-02-05 8:56 ` David Hildenbrand
2020-02-05 8:56 ` David Hildenbrand
2020-02-05 9:00 ` Wang, Wei W
2020-02-05 9:00 ` Wang, Wei W
2020-02-05 9:05 ` David Hildenbrand
2020-02-05 9:05 ` David Hildenbrand
2020-02-05 9:19 ` Wang, Wei W
2020-02-05 9:19 ` Wang, Wei W
2020-02-05 9:22 ` David Hildenbrand
2020-02-05 9:22 ` David Hildenbrand
2020-02-05 9:35 ` Wang, Wei W
2020-02-05 9:35 ` Wang, Wei W
2020-02-05 9:37 ` David Hildenbrand
2020-02-05 9:37 ` David Hildenbrand
2020-02-05 9:49 ` Wang, Wei W
2020-02-05 9:49 ` Wang, Wei W
2020-02-05 9:58 ` David Hildenbrand
2020-02-05 9:58 ` David Hildenbrand
2020-02-05 10:25 ` Michael S. Tsirkin
2020-02-05 10:25 ` Michael S. Tsirkin
2020-02-05 10:42 ` David Hildenbrand
2020-02-05 10:42 ` David Hildenbrand
2020-02-05 9:35 ` Michael S. Tsirkin
2020-02-05 9:35 ` Michael S. Tsirkin
2020-02-05 18:43 ` Tyler Sanderson via Virtualization
2020-02-05 18:43 ` Tyler Sanderson
2020-02-06 9:30 ` Wang, Wei W
2020-02-06 9:30 ` Wang, Wei W
2020-02-05 7:35 ` Nadav Amit via Virtualization
2020-02-05 7:35 ` Nadav Amit
2020-02-05 8:19 ` David Hildenbrand
2020-02-05 8:19 ` David Hildenbrand
2020-02-05 10:27 ` Michael S. Tsirkin
2020-02-05 10:27 ` Michael S. Tsirkin
2020-02-05 10:43 ` David Hildenbrand
2020-02-05 10:43 ` David Hildenbrand
2020-01-30 22:46 ` Tyler Sanderson via Virtualization
2020-01-30 22:46 ` Tyler Sanderson
2020-02-02 0:21 ` David Rientjes via Virtualization
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