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=ham 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 E93EDC43381 for ; Wed, 13 Mar 2019 13:08:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A7F08214AE for ; Wed, 13 Mar 2019 13:08:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726562AbfCMNIq (ORCPT ); Wed, 13 Mar 2019 09:08:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47218 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725888AbfCMNIq (ORCPT ); Wed, 13 Mar 2019 09:08:46 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 93C6640F45; Wed, 13 Mar 2019 13:08:45 +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 17D346B8D5; Wed, 13 Mar 2019 13:08:34 +0000 (UTC) From: Nitesh Narayan Lal To: David Hildenbrand Cc: "Michael S. Tsirkin" , 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 , Alexander Duyck Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages References: <20190306155048.12868-1-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> <41ae8afe-72c9-58e6-0cbb-9375c91ce37a@redhat.com> <1ae522f1-1e98-9eef-324c-29585fe574d6@redhat.com> <8826829a-973d-8117-3fe3-8e33170acfb8@redhat.com> Organization: Red Hat Inc, Message-ID: <01a7e65a-fd17-3bfa-8350-c44065761bd5@redhat.com> Date: Wed, 13 Mar 2019 09:08:30 -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: <8826829a-973d-8117-3fe3-8e33170acfb8@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Ek4TzUhYxEXa0KQk26odtDuW1poCxLMMZ" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 13 Mar 2019 13:08:45 +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) --Ek4TzUhYxEXa0KQk26odtDuW1poCxLMMZ Content-Type: multipart/mixed; boundary="3Ig4s7Qeq3zXTtE58FZepklsBVvKXQ91F"; protected-headers="v1" From: Nitesh Narayan Lal To: David Hildenbrand Cc: "Michael S. Tsirkin" , 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 , Alexander Duyck Message-ID: <01a7e65a-fd17-3bfa-8350-c44065761bd5@redhat.com> Subject: Re: [RFC][Patch v9 2/6] KVM: Enables the kernel to isolate guest free pages --3Ig4s7Qeq3zXTtE58FZepklsBVvKXQ91F Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 3/13/19 8:17 AM, David Hildenbrand wrote: > On 13.03.19 12:54, Nitesh Narayan Lal wrote: >> On 3/12/19 5:13 PM, Alexander Duyck wrote: >>> On Tue, Mar 12, 2019 at 12:46 PM Nitesh Narayan Lal wrote: >>>> 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 wrot= e: >>>>>>>>>>> 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 b= uddy >>>>>>>>>>> pages. >>>>>>>>>> Actually there's one extra thing I think we should do, and tha= t is make >>>>>>>>>> sure we do not leave less than X% off the free memory at a tim= e. >>>>>>>>>> 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= memory >>>>>>>>> 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 i= t >>>>>>> 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 short= ly >>>>>>> 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 st= ay >>>>>>> free for a while. >>>>>>> >>>>>>>>> It is another reason why we >>>>>>>>> probably want a bit in the buddy pages somewhere to indicate if= a page >>>>>>>>> has been hinted or not as we can then use that to determine if = we have >>>>>>>>> to account for it in the statistics. >>>>>>>> The one benefit which I can see of having an explicit bit is tha= t 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 du= plicate >>>>>>>> hints while releasing pages. >>>>>>>> >>>>>>>> I still have to check PG_idle and PG_young which you mentioned b= ut I >>>>>>>> don't think we can reuse any existing bits. >>>>>>> Those are bits that are already there for 64b. I think those exis= t 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 ar= e the >>>>>>> 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= 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 ma= ny >>>>>>> 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. >>>>> You are correct up to here. When we isolate the page it isn't count= ed >>>>> against the free pages. However after we complete the hint we end u= p >>>>> 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 = pages, >>>>>> is that right? >>>>> Getting back to the ideas from our earlier discussion, we had 3 sta= ges >>>>> 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 fir= st >>>>> pool that is free and not hinted by knowing the total number of fre= e >>>>> 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 curr= ent >>>> 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. >>> I'm not sure what you are talking about by "avoid any locking in the >>> allocation path". Are you talking about the spin on idle bit, if so >>> then yes.=20 >> Yeap! >>> However I have been testing your patches and I was correct >>> in the assumption that you forgot to handle the zone lock when you >>> were freeing __free_one_page. >> Yes, these are the steps other than the comments you provided in the >> code. (One of them is to fix release_buddy_page()) >>> I just did a quick copy/paste from your >>> zone lock handling from the guest_free_page_hinting function into the= >>> release_buddy_pages function and then I was able to enable multiple >>> CPUs without any issues. >>> >>>> For the next step other than the comments received in the code and w= hat >>>> I mentioned in the cover email, I would like to do the following: >>>> 1. Explore the watermark idea suggested by Alex and bring down memho= g >>>> execution time if possible. >>> So there are a few things that are hurting us on the memhog test: >>> 1. The current QEMU patch is only madvising 4K pages at a time, this >>> is disabling THP and hurts the test. >> Makes sense, thanks for pointing this out. >>> 2. The fact that we madvise the pages away makes it so that we have t= o >>> fault the page back in in order to use it for the memhog test. In >>> order to avoid that penalty we may want to see if we can introduce >>> some sort of "timeout" on the pages so that we are only hinting away >>> old pages that have not been used for some period of time. >> Possibly using MADVISE_FREE should also help in this, I will try this = as >> well. > I was asking myself some time ago how MADVISE_FREE will be handled in > case of THP. Please let me know your findings :) I will do that. If we don't end up finding any appropriate page flag to track the age of free page. I am wondering if I can somehow use bitmap to track the free count for each PFN. > --=20 Regards Nitesh --3Ig4s7Qeq3zXTtE58FZepklsBVvKXQ91F-- --Ek4TzUhYxEXa0KQk26odtDuW1poCxLMMZ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAlyJAM8ACgkQo4ZA3AYy oznKeg//TzdsmVxg5nia+SpRaUxiEGYJEJkeHKnVLqz+oRShWZQkEFBYumUh2mBH SP+bsvOVtptdVOyg9KLh6KQl7vmXkmXrkK/xv78zzFGgmgNnQdTbZN5KAwCDbQJK fuj0kzsJTwI2mdktQsQhJ2CLjNJ//HLYbVHDxO18Ysggf55ubnpJkzyXYjyykW6K JQPrpO8++tMwrS6SN8xG8yK9jafVfoppSM9PaoBLrtlZpdGa/QoAwVkjEA0FlGHs WmipLp5B3vKdJoM7/4C5iY0OQ3oZrzKdXxkjdulNVK2j6QgzDs2GV7g6Q/N3euIe WG3Tuvx0uOPmU9EQNk5iIKswlh3GBM5lImxrAQdXw2I4OfIwUsiSdej30cmEy/iI zWcvz+RnXy3tBYpjX02rxZECz/ITlA6MSs2u4UkOcXSJo6O0y+3AJXY+vIwiNfIv 69485p2J1pXUBr8+p+sI/LAdTpBtVL+NUmTPyF70dezPKU/gFlawydYFV/yLICj5 7tDp2CW/Xg3a/ro8mjVwt6gZDp6MeA4XDKK2uAFkKIT16mWvB53EqsrlusUOfAgE 6nyHIZiu31sqmoW+LmOvLCcuDyJyptv1oHySAX4xDn99ifTQl8QQm4B4Sd0fV6Gf DlveoktVR/uffbHVPxdUEmgQR9KsR7kKDu0lRQd3rekYONy1QQg= =ULLn -----END PGP SIGNATURE----- --Ek4TzUhYxEXa0KQk26odtDuW1poCxLMMZ--