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[91.12.106.69]) by smtp.gmail.com with ESMTPSA id s22sm8652442wmh.4.2020.02.14.13.17.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2020 13:17:27 -0800 (PST) From: David Hildenbrand Mime-Version: 1.0 (1.0) 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 22:17:26 +0100 Message-Id: <8B1B3CD6-10D5-46D3-B8E5-A6AD0B8E41BC@redhat.com> References: Cc: David Hildenbrand , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org, "Michael S . Tsirkin" , Wei Wang , Alexander Duyck , David Rientjes , Nadav Amit In-Reply-To: To: Tyler Sanderson X-Mailer: iPhone Mail (17D50) X-MC-Unique: m1GusBrJMcuYWgTHpgPKFg-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary=Apple-Mail-3738AA56-3B37-4F6D-A815-7B956B2B47A0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --Apple-Mail-3738AA56-3B37-4F6D-A815-7B956B2B47A0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable > Am 14.02.2020 um 21:49 schrieb Tyler Sanderson : >=20 > =EF=BB=BF > Regarding Wei's patch that modifies the shrinker implementation, versus t= his patch which reverts to OOM notifier: > I am in favor of both patches. But I do want to make sure a fix gets back= ported to 4.19 where the performance regression was first introduced. > My concern with reverting to the OOM notifier is, as mst@ put it (in the = other thread): > "when linux hits OOM all kind of error paths are being hit, latent bugs s= tart triggering, latency goes up drastically." Yeah, and that was the default behavior for years, so it=E2=80=98s not big = news :) > The guest could be in a lot of pain before the OOM notifier is invoked, a= nd it seems like the shrinker API might allow more fine grained control of = when we deflate. >=20 > On the other hand, I'm not totally convinced that Wei's patch is an expec= ted use of the shrinker/page-cache APIs, and maybe it is fragile. Needs mor= e testing and scrutiny. >=20 > It seems to me like the shrinker API is the right API in the long run, pe= rhaps with some fixes and modifications. But maybe reverting to OOM notifie= r is the best patch to back I think that=E2=80=98s a good idea. Revert to the old state we had for year= s and then implement a proper, fully tested solution (e.g., shrinkers with = priorities). Cheers! --Apple-Mail-3738AA56-3B37-4F6D-A815-7B956B2B47A0 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable


Am 14.02.2020 um 21:49 schrieb Tyler San= derson <tysand@google.com>:

=EF=BB=BF
Regarding Wei's = patch that modifies the shrinker implementation, versus this patch which re= verts to OOM notifier:
I am in favor of both patches. But I do wa= nt to make sure a fix gets back ported to 4.19 where the performance regres= sion was first introduced.
My concern with reverting to the OOM n= otifier is, as mst@ put it (in the other thread):
"when linux hits OOM all kind of error paths are being hit, latent bugs start triggering,&= nbsp;latency goes up drastically.= "

Yeah, and th= at was the default behavior for years, so it=E2=80=98s not big news :)
The g= uest could be in a lot of pain before the OOM notifier is invoked, and it s= eems like the shrinker API might allow more fine grained control of when we= deflate.

On the other hand, I'm not totally convi= nced that Wei's patch is an expected use of the shrinker/page-cache APIs, a= nd maybe it is fragile. Needs more testing and scrutiny.
It seems to me like the shrinker API is the right API in the lo= ng run, perhaps with some fixes and modifications. But maybe reverting to O= OM notifier is the best patch to back

I think that=E2=80=98s a good idea. Revert to the old state we had for ye= ars and then implement a proper, fully tested solution (e.g., shrinkers wit= h priorities).

Cheers!
--Apple-Mail-3738AA56-3B37-4F6D-A815-7B956B2B47A0--