From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BAFCC10F00 for ; Tue, 12 Mar 2019 19:46:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 046C2214AF for ; Tue, 12 Mar 2019 19:46:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726930AbfCLTqc (ORCPT ); Tue, 12 Mar 2019 15:46:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36688 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726775AbfCLTqb (ORCPT ); Tue, 12 Mar 2019 15:46:31 -0400 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 0C1EA8F860; Tue, 12 Mar 2019 19:46:31 +0000 (UTC) Received: from [10.18.17.32] (dhcp-17-32.bos.redhat.com [10.18.17.32]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5E22660BF7; Tue, 12 Mar 2019 19:46:19 +0000 (UTC) From: Nitesh Narayan Lal To: Alexander Duyck , "Michael S. Tsirkin" Cc: 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> <8f692047-4750-6827-1ee0-d3d354788f09@redhat.com> Organization: Red Hat Inc, Message-ID: <41ae8afe-72c9-58e6-0cbb-9375c91ce37a@redhat.com> Date: Tue, 12 Mar 2019 15:46:15 -0400 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="OxKmVXZle8XZPHQokqhweRMEdqZsPL0jS" 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 [10.5.110.27]); Tue, 12 Mar 2019 19:46:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --OxKmVXZle8XZPHQokqhweRMEdqZsPL0jS Content-Type: multipart/mixed; boundary="Q2ysSGlqobWbBDV2hKjOD9Aas8wcksB0W"; protected-headers="v1" From: Nitesh Narayan Lal To: Alexander Duyck , "Michael S. Tsirkin" Cc: 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: <41ae8afe-72c9-58e6-0cbb-9375c91ce37a@redhat.com> Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages --Q2ysSGlqobWbBDV2hKjOD9Aas8wcksB0W Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 3/8/19 4:39 PM, Alexander Duyck wrote: > On Fri, Mar 8, 2019 at 11:39 AM Nitesh Narayan Lal = wrote: >> 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 = wrote: >>>>>> 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 t= o 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= make >>>>>> 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 befo= re >>>>> 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 mem= ory >>>>> 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 p= age >>>>> has been hinted or not as we can then use that to determine if we h= ave >>>>> 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 bud= dy >>>> merging code (just like your arch_merge_page) and still avoid duplic= ate >>>> 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 onl= y >>> used in VMA mapped memory. What I was getting at is that those are th= e >>> bits we could think about reusing. >>> >>>> If we really want to have something like a watermark, then can't we = use >>>> zone->free_pages before isolating to see how many free pages are the= re >>>> and put a threshold on it? (__isolate_free_page() does a similar thi= ng >>>> 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 mor= e >>> 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. > You are correct up to here. When we isolate the page it isn't counted > against the free pages. However after we complete the hint we end up > taking it out of isolation and returning it to the "free" state, so it > will be counted against the free pages. > >> If I am understanding it correctly you only want to hint the idle page= s, >> is that right? > Getting back to the ideas from our earlier discussion, we had 3 stages > for things. Free but not hinted, isolated due to hinting, and free and > hinted. So what we would need to do is identify the size of the first > pool that is free and not hinted by knowing the total number of free > pages, and then subtract the size of the pages that are hinted and > still free. To summarize, for now, I think it makes sense to stick with the current approach as this way we can avoid any locking in the allocation path and reduce the number of hypercalls for a bunch of MAX_ORDER - 1 page. For the next step other than the comments received in the code and what I mentioned in the cover email, I would like to do the following: 1. Explore the watermark idea suggested by Alex and bring down memhog execution time if possible. 2. Benchmark hinting v/s non-hinting more extensively. Let me know if you have any specific suggestions in terms of the tools I can run to do the same. (I am planning to run atleast netperf, hackbench and stress for this). > >>>>>>> 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 = van >>>>>> Riel and him saying it's actually better to take away recently use= d >>>>>> 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 t= o >>>>> populate the last page we were working on. The sweet spot will be t= hat >>>>> period of time that is somewhere in between so we don't trigger >>>>> unnecessary page faults and we don't need to perform additional swa= p >>>>> reads/writes. >>>> -- >>>> Regards >>>> Nitesh >>>> >> -- >> Regards >> Nitesh >> --=20 Regards Nitesh --Q2ysSGlqobWbBDV2hKjOD9Aas8wcksB0W-- --OxKmVXZle8XZPHQokqhweRMEdqZsPL0jS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAlyIDIgACgkQo4ZA3AYy ozl16w/+MPhJBHsfQs21XCb5Af8Ndn4Co95IeNoLaEbrqQlD+MovTAQhDLvOOltv eym/pc5iyzw1Uhma1LVjzVpRFH5Y9t+6VWRG0/hPNtNKNifzLC8jGAaxDVXZoJBW b47h1nFMImOaiE2OdFPyEPAxIAGMD4TGmHOUzZOAmD2181Q0lbjdleczK6anBhap cLpyUwZ9OlCAQlcJh6dQrZCHa/JG9ux6LP3mGMQMV3kndvw/OkWuB1MCN2T32NTS WmIdDBW3slioJX+YlIAlpaCVaZnIQRVR/b0gqboX8xAEIhMakh42DUZ8wDfRpHjC Y9pFLo8nTSUQ6oNTkHDlrfpmKOnUp8Qet8WhSGkyZLQdGA1NpLzngi8FPzlsq6ue kbUP1EkRP9UB0bCt47kat/C4ZSfgvR94Nh4aE0oU71iCcPM/lcHSI8F67nqKtphP /26tZoawnVIHPggNCY/kj2q/t5EIrqUdgY3wg0xoQnHigj75d3NM7sNq3vPcAexN DikwWwpaivcEt5Ff8CxsK41vqPRJ+X4XFizViYlUSjc0hQxMTLeqAkK68HtJ8b03 gOW6wshrcobFN2I/f7YIKGW5aJVEu6EGhxyyLVZo1KW46PGHPWSIrk9eVfpRvAb0 wREMTYRi/4u3/vT9CScZIh0I8aH/mI/pPX4iQHUpUbS29FfyvAI= =c52/ -----END PGP SIGNATURE----- --OxKmVXZle8XZPHQokqhweRMEdqZsPL0jS--