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[209.132.183.28]) by mx.google.com with ESMTPS id a2si5352186qvd.95.2019.03.08.11.39.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Mar 2019 11:39:20 -0800 (PST) Received-SPF: pass (google.com: domain of nitesh@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of nitesh@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=nitesh@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DDFF781E19; Fri, 8 Mar 2019 19:39:18 +0000 (UTC) Received: from [10.40.205.251] (unknown [10.40.205.251]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 10C951690F; Fri, 8 Mar 2019 19:39:00 +0000 (UTC) From: Nitesh Narayan Lal To: Alexander Duyck Cc: "Michael S. Tsirkin" , David Hildenbrand , kvm list , LKML , linux-mm , Paolo Bonzini , lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, Yang Zhang , Rik van Riel , dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages References: <20190306155048.12868-1-nitesh@redhat.com> <20190306155048.12868-3-nitesh@redhat.com> <2d9ae889-a9b9-7969-4455-ff36944f388b@redhat.com> <22e4b1cd-38a5-6642-8cbe-d68e4fcbb0b7@redhat.com> <78b604be-2129-a716-a7a6-f5b382c9fb9c@redhat.com> <20190307212845-mutt-send-email-mst@kernel.org> <17d2afa6-556e-ec73-40dc-beac536b3f20@redhat.com> Organization: Red Hat Inc, Message-ID: <8f692047-4750-6827-1ee0-d3d354788f09@redhat.com> Date: Fri, 8 Mar 2019 14:38:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="8V13K9q11cPOiDPproSx8qZXs1NSfkUuj" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 08 Mar 2019 19:39:19 +0000 (UTC) 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: This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --8V13K9q11cPOiDPproSx8qZXs1NSfkUuj Content-Type: multipart/mixed; boundary="f4QJr4T5d62WyAt2NEZJ9Bhrbh7HvhH7s"; protected-headers="v1" From: Nitesh Narayan Lal To: Alexander Duyck Cc: "Michael S. Tsirkin" , David Hildenbrand , kvm list , LKML , linux-mm , Paolo Bonzini , lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, Yang Zhang , Rik van Riel , dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli Message-ID: <8f692047-4750-6827-1ee0-d3d354788f09@redhat.com> Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages --f4QJr4T5d62WyAt2NEZJ9Bhrbh7HvhH7s Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 3/8/19 2:25 PM, Alexander Duyck wrote: > On Fri, Mar 8, 2019 at 11:10 AM Nitesh Narayan Lal = wrote: >> >> On 3/8/19 1:06 PM, Alexander Duyck wrote: >>> On Thu, Mar 7, 2019 at 6:32 PM Michael S. Tsirkin wr= ote: >>>> On Thu, Mar 07, 2019 at 02:35:53PM -0800, Alexander Duyck wrote: >>>>> The only other thing I still want to try and see if I can do is to = add >>>>> a jiffies value to the page private data in the case of the buddy >>>>> pages. >>>> Actually there's one extra thing I think we should do, and that is m= ake >>>> sure we do not leave less than X% off the free memory at a time. >>>> This way chances of triggering an OOM are lower. >>> If nothing else we could probably look at doing a watermark of some >>> sort so we have to have X amount of memory free but not hinted before= >>> we will start providing the hints. It would just be a matter of >>> tracking how much memory we have hinted on versus the amount of memor= y >>> that has been pulled from that pool. >> This is to avoid false OOM in the guest? > Partially, though it would still be possible. Basically it would just > be a way of determining when we have hinted "enough". Basically it > doesn't do us much good to be hinting on free memory if the guest is > already constrained and just going to reallocate the memory shortly > after we hinted on it. The idea is with a watermark we can avoid > hinting until we start having pages that are actually going to stay > free for a while. > >>> It is another reason why we >>> probably want a bit in the buddy pages somewhere to indicate if a pag= e >>> has been hinted or not as we can then use that to determine if we hav= e >>> to account for it in the statistics. >> The one benefit which I can see of having an explicit bit is that it >> will help us to have a single hook away from the hot path within buddy= >> merging code (just like your arch_merge_page) and still avoid duplicat= e >> hints while releasing pages. >> >> I still have to check PG_idle and PG_young which you mentioned but I >> don't think we can reuse any existing bits. > Those are bits that are already there for 64b. I think those exist in > the page extension for 32b systems. If I am not mistaken they are only > used in VMA mapped memory. What I was getting at is that those are the > bits we could think about reusing. > >> If we really want to have something like a watermark, then can't we us= e >> zone->free_pages before isolating to see how many free pages are there= >> and put a threshold on it? (__isolate_free_page() does a similar thing= >> but it does that on per request basis). > Right. That is only part of it though since that tells you how many > free pages are there. But how many of those free pages are hinted? > That is the part we would need to track separately and then then > compare to free_pages to determine if we need to start hinting on more > memory or not. Only pages which are isolated will be hinted, and once a page is isolated it will not be counted in the zone free pages. Feel free to correct me if I am wrong. If I am understanding it correctly you only want to hint the idle pages, is that right? > >>>>> With that we could track the age of the page so it becomes >>>>> easier to only target pages that are truly going cold rather than >>>>> trying to grab pages that were added to the freelist recently. >>>> I like that but I have a vague memory of discussing this with Rik va= n >>>> Riel and him saying it's actually better to take away recently used >>>> ones. Can't see why would that be but maybe I remember wrong. Rik - = am I >>>> just confused? >>> It is probably to cut down on the need for disk writes in the case of= >>> swap. If that is the case it ends up being a trade off. >>> >>> The sooner we hint the less likely it is that we will need to write a= >>> given page to disk. However the sooner we hint, the more likely it is= >>> we will need to trigger a page fault and pull back in a zero page to >>> populate the last page we were working on. The sweet spot will be tha= t >>> period of time that is somewhere in between so we don't trigger >>> unnecessary page faults and we don't need to perform additional swap >>> reads/writes. >> -- >> Regards >> Nitesh >> --=20 Regards Nitesh --f4QJr4T5d62WyAt2NEZJ9Bhrbh7HvhH7s-- --8V13K9q11cPOiDPproSx8qZXs1NSfkUuj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAlyCxNAACgkQo4ZA3AYy ozl3oRAAia5Dz2avOmKr/a1Ev84UQjMmuObxBysvEemwv6N1ZTU+nlC7CXOk1jx5 Kk6dIaPn70vs8i4D6eZs0Uh/ocedS5bXgEUKvvxPaSyZzti4QaoG0SPUWqrbQzlr 5N6fhcaXmJsIkSNKhcMGdz7gOGXeOn7xjTICT60GAZFTECLVqY4Nh6HjAGtVCeUA pzVydsO96pS4f7nE1+jOsAo18RIqpyrArzFHHQMVlD0STpJBGf4xoXJOWYz3D+MB 509GeqjptMe6kBAxK9ZLxFWgmvBvHKBzHnytKNLxfBHs7AuvdOzPooz6WbO5cWth RhMb9ffIwkve7nDJGCAjK51aVoc+lajvCkzQNjFu1la+syCNihA1vAqShA4U9WSJ TyFSYMpQ1ZoI0uJl4E2g6FxbQ/EqosMjvTmNG0QoP7zpyJ+aa8HSTbfkFSdQ6UxL N08gXgdis1iq3q4u9N4zTL8Xzp2paF3jKpW9/NzRlR/DmPI9so30mnywT5cQcnDZ XT3XLbhg+MxO2P3e9iDgozHDxptxYtf01KJIMJm+JFTFagQ8i1AMHVsswwg88pQc h1xTfl1xMh+gehhxGf4gk5vJY8c7Raoq9/ZqiIdxY67xpwIy+zuGGagowvpXcBz/ kNNG4KeSUHPWBfGmb2GMg6/WhNY5RJ4deke8B/rWqRpx6dDHSSk= =n2GA -----END PGP SIGNATURE----- --8V13K9q11cPOiDPproSx8qZXs1NSfkUuj--