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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 81EC0C32753 for ; Wed, 14 Aug 2019 12:49:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 583E42083B for ; Wed, 14 Aug 2019 12:49:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727685AbfHNMtl convert rfc822-to-8bit (ORCPT ); Wed, 14 Aug 2019 08:49:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53134 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726365AbfHNMtl (ORCPT ); Wed, 14 Aug 2019 08:49:41 -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 9932A300BEB1; Wed, 14 Aug 2019 12:49:40 +0000 (UTC) Received: from [10.18.17.163] (dhcp-17-163.bos.redhat.com [10.18.17.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EF48D805FA; Wed, 14 Aug 2019 12:49:32 +0000 (UTC) Subject: Re: [virtio-dev] Re: [RFC][Patch v12 1/2] mm: page_reporting: core infrastructure To: David Hildenbrand , Alexander Duyck Cc: kvm list , LKML , linux-mm , virtio-dev@lists.oasis-open.org, Paolo Bonzini , lcapitulino@redhat.com, Pankaj Gupta , "Wang, Wei W" , Yang Zhang , Rik van Riel , "Michael S. Tsirkin" , dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli , john.starks@microsoft.com, Dave Hansen , Michal Hocko , cohuck@redhat.com References: <20190812131235.27244-1-nitesh@redhat.com> <20190812131235.27244-2-nitesh@redhat.com> <32f61f87-6205-5001-866c-a84e20fc9d85@redhat.com> <3409b5cc-59e0-28d2-de5f-aa7cadaf434c@redhat.com> From: Nitesh Narayan Lal Openpgp: preference=signencrypt Autocrypt: addr=nitesh@redhat.com; prefer-encrypt=mutual; keydata= mQINBFl4pQoBEADT/nXR2JOfsCjDgYmE2qonSGjkM1g8S6p9UWD+bf7YEAYYYzZsLtbilFTe z4nL4AV6VJmC7dBIlTi3Mj2eymD/2dkKP6UXlliWkq67feVg1KG+4UIp89lFW7v5Y8Muw3Fm uQbFvxyhN8n3tmhRe+ScWsndSBDxYOZgkbCSIfNPdZrHcnOLfA7xMJZeRCjqUpwhIjxQdFA7 n0s0KZ2cHIsemtBM8b2WXSQG9CjqAJHVkDhrBWKThDRF7k80oiJdEQlTEiVhaEDURXq+2XmG jpCnvRQDb28EJSsQlNEAzwzHMeplddfB0vCg9fRk/kOBMDBtGsTvNT9OYUZD+7jaf0gvBvBB lbKmmMMX7uJB+ejY7bnw6ePNrVPErWyfHzR5WYrIFUtgoR3LigKnw5apzc7UIV9G8uiIcZEn C+QJCK43jgnkPcSmwVPztcrkbC84g1K5v2Dxh9amXKLBA1/i+CAY8JWMTepsFohIFMXNLj+B RJoOcR4HGYXZ6CAJa3Glu3mCmYqHTOKwezJTAvmsCLd3W7WxOGF8BbBjVaPjcZfavOvkin0u DaFvhAmrzN6lL0msY17JCZo046z8oAqkyvEflFbC0S1R/POzehKrzQ1RFRD3/YzzlhmIowkM BpTqNBeHEzQAlIhQuyu1ugmQtfsYYq6FPmWMRfFPes/4JUU/PQARAQABtCVOaXRlc2ggTmFy YXlhbiBMYWwgPG5pbGFsQHJlZGhhdC5jb20+iQI9BBMBCAAnBQJZeKUKAhsjBQkJZgGABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheAAAoJEKOGQNwGMqM56lEP/A2KMs/pu0URcVk/kqVwcBhU SnvB8DP3lDWDnmVrAkFEOnPX7GTbactQ41wF/xwjwmEmTzLrMRZpkqz2y9mV0hWHjqoXbOCS 6RwK3ri5e2ThIPoGxFLt6TrMHgCRwm8YuOSJ97o+uohCTN8pmQ86KMUrDNwMqRkeTRW9wWIQ EdDqW44VwelnyPwcmWHBNNb1Kd8j3xKlHtnS45vc6WuoKxYRBTQOwI/5uFpDZtZ1a5kq9Ak/ MOPDDZpd84rqd+IvgMw5z4a5QlkvOTpScD21G3gjmtTEtyfahltyDK/5i8IaQC3YiXJCrqxE r7/4JMZeOYiKpE9iZMtS90t4wBgbVTqAGH1nE/ifZVAUcCtycD0f3egX9CHe45Ad4fsF3edQ ESa5tZAogiA4Hc/yQpnnf43a3aQ67XPOJXxS0Qptzu4vfF9h7kTKYWSrVesOU3QKYbjEAf95 NewF9FhAlYqYrwIwnuAZ8TdXVDYt7Z3z506//sf6zoRwYIDA8RDqFGRuPMXUsoUnf/KKPrtR ceLcSUP/JCNiYbf1/QtW8S6Ca/4qJFXQHp0knqJPGmwuFHsarSdpvZQ9qpxD3FnuPyo64S2N Dfq8TAeifNp2pAmPY2PAHQ3nOmKgMG8Gn5QiORvMUGzSz8Lo31LW58NdBKbh6bci5+t/HE0H pnyVf5xhNC/FuQINBFl4pQoBEACr+MgxWHUP76oNNYjRiNDhaIVtnPRqxiZ9v4H5FPxJy9UD Bqr54rifr1E+K+yYNPt/Po43vVL2cAyfyI/LVLlhiY4yH6T1n+Di/hSkkviCaf13gczuvgz4 KVYLwojU8+naJUsiCJw01MjO3pg9GQ+47HgsnRjCdNmmHiUQqksMIfd8k3reO9SUNlEmDDNB XuSzkHjE5y/R/6p8uXaVpiKPfHoULjNRWaFc3d2JGmxJpBdpYnajoz61m7XJlgwl/B5Ql/6B dHGaX3VHxOZsfRfugwYF9CkrPbyO5PK7yJ5vaiWre7aQ9bmCtXAomvF1q3/qRwZp77k6i9R3 tWfXjZDOQokw0u6d6DYJ0Vkfcwheg2i/Mf/epQl7Pf846G3PgSnyVK6cRwerBl5a68w7xqVU 4KgAh0DePjtDcbcXsKRT9D63cfyfrNE+ea4i0SVik6+N4nAj1HbzWHTk2KIxTsJXypibOKFX 2VykltxutR1sUfZBYMkfU4PogE7NjVEU7KtuCOSAkYzIWrZNEQrxYkxHLJsWruhSYNRsqVBy KvY6JAsq/i5yhVd5JKKU8wIOgSwC9P6mXYRgwPyfg15GZpnw+Fpey4bCDkT5fMOaCcS+vSU1 UaFmC4Ogzpe2BW2DOaPU5Ik99zUFNn6cRmOOXArrryjFlLT5oSOe4IposgWzdwARAQABiQIl BBgBCAAPBQJZeKUKAhsMBQkJZgGAAAoJEKOGQNwGMqM5ELoP/jj9d9gF1Al4+9bngUlYohYu 0sxyZo9IZ7Yb7cHuJzOMqfgoP4tydP4QCuyd9Q2OHHL5AL4VFNb8SvqAxxYSPuDJTI3JZwI7 d8JTPKwpulMSUaJE8ZH9n8A/+sdC3CAD4QafVBcCcbFe1jifHmQRdDrvHV9Es14QVAOTZhnJ vweENyHEIxkpLsyUUDuVypIo6y/Cws+EBCWt27BJi9GH/EOTB0wb+2ghCs/i3h8a+bi+bS7L FCCm/AxIqxRurh2UySn0P/2+2eZvneJ1/uTgfxnjeSlwQJ1BWzMAdAHQO1/lnbyZgEZEtUZJ x9d9ASekTtJjBMKJXAw7GbB2dAA/QmbA+Q+Xuamzm/1imigz6L6sOt2n/X/SSc33w8RJUyor SvAIoG/zU2Y76pKTgbpQqMDmkmNYFMLcAukpvC4ki3Sf086TdMgkjqtnpTkEElMSFJC8npXv 3QnGGOIfFug/qs8z03DLPBz9VYS26jiiN7QIJVpeeEdN/LKnaz5LO+h5kNAyj44qdF2T2AiF HxnZnxO5JNP5uISQH3FjxxGxJkdJ8jKzZV7aT37sC+Rp0o3KNc+GXTR+GSVq87Xfuhx0LRST NK9ZhT0+qkiN7npFLtNtbzwqaqceq3XhafmCiw8xrtzCnlB/C4SiBr/93Ip4kihXJ0EuHSLn VujM7c/b4pps Organization: Red Hat Inc, Message-ID: <1833c84f-3fdf-759c-aafe-5aba809a6e74@redhat.com> Date: Wed, 14 Aug 2019 08:49:32 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <3409b5cc-59e0-28d2-de5f-aa7cadaf434c@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US 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 [10.5.110.40]); Wed, 14 Aug 2019 12:49:40 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 8/14/19 3:07 AM, David Hildenbrand wrote: > On 14.08.19 01:14, Alexander Duyck wrote: >> On Tue, Aug 13, 2019 at 3:34 AM David Hildenbrand wrote: >>>>>>> +static int process_free_page(struct page *page, >>>>>>> + struct page_reporting_config *phconf, int count) >>>>>>> +{ >>>>>>> + int mt, order, ret = 0; >>>>>>> + >>>>>>> + mt = get_pageblock_migratetype(page); >>>>>>> + order = page_private(page); >>>>>>> + ret = __isolate_free_page(page, order); >>>>>>> + >>>>> I just started looking into the wonderful world of >>>>> isolation/compaction/migration. >>>>> >>>>> I don't think saving/restoring the migratetype is correct here. AFAIK, >>>>> MOVABLE/UNMOVABLE/RECLAIMABLE is just a hint, doesn't mean that e.g., >>>>> movable pages and up in UNMOVABLE or ordinary kernel allocations on >>>>> MOVABLE. So that shouldn't be an issue - I guess. >>>>> >>>>> 1. You should never allocate something that is no >>>>> MOVABLE/UNMOVABLE/RECLAIMABLE. Especially not, if you have ISOLATE or >>>>> CMA here. There should at least be a !is_migrate_isolate_page() check >>>>> somewhere >>>>> >>>>> 2. set_migratetype_isolate() takes the zone lock, so to avoid racing >>>>> with isolation code, you have to hold the zone lock. Your code seems to >>>>> do that, so at least you cannot race against isolation. >>>>> >>>>> 3. You could end up temporarily allocating something in the >>>>> ZONE_MOVABLE. The pages you allocate are, however, not movable. There >>>>> would have to be a way to make alloc_contig_range()/offlining code >>>>> properly wait until the pages have been processed. Not sure about the >>>>> real implications, though - too many details in the code (I wonder if >>>>> Alex' series has a way of dealing with that) >>>>> >>>>> When you restore the migratetype, you could suddenly overwrite e.g., >>>>> ISOLATE, which feels wrong. >>>> >>>> I was triggering an occasional CPU stall bug earlier, with saving and restoring >>>> the migratetype I was able to fix it. >>>> But I will further look into this to figure out if it is really required. >>>> >>> You should especially look into handling isolated/cma pages. Maybe that >>> was the original issue. Alex seems to have added that in his latest >>> series (skipping isolated/cma pageblocks completely) as well. >> So as far as skipping isolated pageblocks, I get the reason for >> skipping isolated, but why would we need to skip CMA? I had made the >> change I did based on comments you had made earlier. But while working >> on some of the changes to address isolation better and looking over >> several spots in the code it seems like CMA is already being used as >> an allocation fallback for MIGRATE_MOVABLE. If that is the case >> wouldn't it make sense to allow pulling pages and reporting them while >> they are in the free_list? > I was assuming that CMA is also to be skipped because "static int > fallbacks[MIGRATE_TYPES][4]" in mm/page_alloc.c doesn't handle CMA at > all, meaning we should never fallback to CMA or from CMA to another type > - at least when stealing pages from another migratetype. So it smells > like MIGRATE_CMA is static -> the area is marked once and will never be > converted to something else (except MIGRATE_ISOLATE temporarily). > > I assume you are talking about gfp_to_alloc_flags()/prepare_alloc_pages(): I am also trying to look into this to get more understanding of it. Another thing which I am looking into right now is the difference between get/set_pcppage_migratetype() and ge/set_pageblock_migratetype(). To an extent, I do understand what is the benefit of using get/set_pcppage_migratetype() by reading the comments. However, I am not sure how it gets along with MIGRATE_CMA. Hopefully, I will have an understanding of it soon. > #ifdef CONFIG_CMA > if (gfpflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE) > alloc_flags |= ALLOC_CMA; > #endif > > Yeah, this looks like MOVABLE allocations can fallback to CMA > pageblocks. And from what I read, "CMA may use its own migratetype > (MIGRATE_CMA) which behaves similarly to ZONE_MOVABLE but can be put in > arbitrary places." > > So I think you are right, it could be that it is safe to temporarily > pull out CMA pages (in contrast to isolated pages) - assuming it is fine > to have temporary unmovable allocations on them (different discussion). > > (I am learning about the details as we discuss :) ) > > The important part would then be to never allocate from the isolated > pageblocks and to never overwrite MIGRATE_ISOLATE. Agreed. I think I should just avoid isolating pages with migratetype MIGRATE_ISOLATE. Adding a check with is_migrate_isolate_page() before isolating the page should do it. > -- Thanks Nitesh