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=-2.5 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 94281C4CEC7 for ; Thu, 12 Sep 2019 12:00:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4771020830 for ; Thu, 12 Sep 2019 12:00:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4771020830 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E8B2A6B0003; Thu, 12 Sep 2019 08:00:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E3B9E6B0005; Thu, 12 Sep 2019 08:00:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE54E6B0006; Thu, 12 Sep 2019 08:00:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id ACAA06B0003 for ; Thu, 12 Sep 2019 08:00:53 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 1AFAF1F209 for ; Thu, 12 Sep 2019 12:00:53 +0000 (UTC) X-FDA: 75926127186.20.angle46_5ef2e47f74c24 X-HE-Tag: angle46_5ef2e47f74c24 X-Filterd-Recvd-Size: 12679 Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by imf43.hostedemail.com (Postfix) with ESMTP for ; Thu, 12 Sep 2019 12:00:52 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F289E10DCC8F; Thu, 12 Sep 2019 12:00:50 +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 75FC05F9C4; Thu, 12 Sep 2019 12:00:46 +0000 (UTC) Subject: Re: [PATCH v9 0/8] stg mail -e --version=v9 \ To: David Hildenbrand , Michal Hocko Cc: "Michael S. Tsirkin" , Alexander Duyck , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm list , Catalin Marinas , Dave Hansen , LKML , Matthew Wilcox , linux-mm , Andrew Morton , will@kernel.org, linux-arm-kernel@lists.infradead.org, Oscar Salvador , Yang Zhang , Pankaj Gupta , Konrad Rzeszutek Wilk , Rik van Riel , lcapitulino@redhat.com, "Wang, Wei W" , Andrea Arcangeli , ying.huang@intel.com, Paolo Bonzini , Dan Williams , Fengguang Wu , "Kirill A. Shutemov" References: <20190911113619.GP4023@dhcp22.suse.cz> <20190911080804-mutt-send-email-mst@kernel.org> <20190911121941.GU4023@dhcp22.suse.cz> <20190911122526.GV4023@dhcp22.suse.cz> <4748a572-57b3-31da-0dde-30138e550c3a@redhat.com> <20190911125413.GY4023@dhcp22.suse.cz> <736594d6-b9ae-ddb9-2b96-85648728ef33@redhat.com> <20190911132002.GA4023@dhcp22.suse.cz> <20190911135100.GC4023@dhcp22.suse.cz> <20190912071633.GL4023@dhcp22.suse.cz> 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: <880cb776-a5c0-026c-6c50-3d8d3c2bb2df@redhat.com> Date: Thu, 12 Sep 2019 08:00:45 -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: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.64]); Thu, 12 Sep 2019 12:00:51 +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: On 9/12/19 3:47 AM, David Hildenbrand wrote: > On 12.09.19 09:16, Michal Hocko wrote: >> On Wed 11-09-19 18:09:18, David Hildenbrand wrote: >>> On 11.09.19 15:51, Michal Hocko wrote: >>>> On Wed 11-09-19 15:20:02, Michal Hocko wrote: >>>> [...] >>>>>> 4. Continuously report, not the "one time report everything" appro= ach. >>>>> So you mean the allocator reporting this rather than an external co= de to >>>>> poll right? I do not know, how much this is nice to have than must = have? >>>> Another idea that I haven't really thought through so it might turne= d >>>> out to be completely bogus but let's try anyway. Your "report everyt= hing" >>>> just made me look and realize that free_pages_prepare already perfor= ms >>>> stuff that actually does something similar yet unrelated. >>>> >>>> We do report to special page poisoning, zeroying or >>>> CONFIG_DEBUG_PAGEALLOC to unmap the address from the kernel address >>>> space. This sounds like something fitting your model no? >>>> >>> AFAIKS, the poisoning/unmapping is done whenever a page is freed. I >>> don't quite see yet how that would help to remember if a page was >>> already reported. >> Do you still have to differ that state when each page is reported? > Ah, very good point. I can see that the reason for this was not > discussed in this thread so far. (Alexander, Nitesh, please correct me > if I am wrong). It's buried in the long history of free page > hinting/reporting. > > Some early patch sets tried to report during every free synchronously. > Free a page, report them to the hypervisor. This resulted in some issue= s > (especially, locking-related and the virtio + the hypervisor being > involved, resulting in unpredictable delays, quite some overhead ...). > It was no good. +1 If I remember correctly then Alexander had posted a patch-set prior to this series where he was reporting every page of a fixed order from __free_one_page(). But as you said it will be costly as it will involve one hypercall per page of reporting_order. > > One design decision then was to not report single pages, but a bunch of= > pages at once. This made it necessary to "remember" the pages to be > reported and to temporarily block them from getting allocated while > reporting. Until my v7 posting [1] I was doing this. We did not proceed with this as blocking allocation was not recommended for reporting. > > Nitesh implemented (at least) two "capture PFNs of free pages in an > array when freeing" approaches. One being synchronous from the freeing > CPU once the list was full (having similar issues as plain synchronous > reporting) and one being asynchronous by a separate thread (which solve= d > many locking issues). One issue with asynchronous + array approach was that it could have lead to false OOMs due to several pages being isolated at the same time. > > Turned out the a simple array can quickly lead to us having to drop > "reports" to the hypervisor because the array is full and the reporting= > thread was not able to keep up. Not good as well. Especially, if some > process frees a lot of memory this can happen quickly and Nitesh wa > sable to trigger this scenario frequently. +1 > > Finally, Nitesh decided to use the bitmap instead to keep track of page= s > to report. I'd like to note that this approach could still be combined > with an "array of potentially free PFNs". Only when the array/circular > buffer runs out of entries ("reporting thread cannot keep up"), we woul= d > have to go back to scanning the bitmap. I will have to think about it. > That was also the point where Alexander decided to look into integratin= g > tracking/handling reported/unreported pages directly in the buddy. > >>> After reporting the page we would have to switch some >>> state (Nitesh: bitmap bit, Alexander: page flag) to identify that. >> Yes, you can either store the state somewhere. >> >>> Of course, we could map the page and treat that as "the state" when w= e >>> reported it, but I am not sure that's such a good idea :) >>> >>> As always, I might be very wrong ... >> I still do not fully understand the usecase so I might be equally wron= g. >> My thinking is along these lines. Why should you scan free pages when >> you can effectively capture each freed page? If you go one step furthe= r >> then post_alloc_hook would be the counterpart to know that your page h= as >> been allocated. > I'd like to note that Nitesh's patch set contains the following hunk, > which is roughly what you were thinking :) > > > -static inline void __free_one_page(struct page *page, > +inline void __free_one_page(struct page *page, > unsigned long pfn, > struct zone *zone, unsigned int order, > - int migratetype) > + int migratetype, bool hint) > { > unsigned long combined_pfn; > unsigned long uninitialized_var(buddy_pfn); > @@ -980,7 +981,8 @@ static inline void __free_one_page(struct page *pag= e, > migratetype); > else > add_to_free_area(page, &zone->free_area[order], migratetype); > - > + if (hint) > + page_hinting_enqueue(page, order); > } > > > (ignore the hint parameter, when he would switch to a isolate vs. > alloc/free, that can go away and all we left is the enqueue part) Precisely. Although, there would be a scenario where the allocation will take place for a page whose order would be < REPORTING_ORDER. In that case, if I decide to ignore all the remaining pages and clear the previously head free page bit, I might end up losing the reporting opportunity. But I can certainly look into this. > > > Inside that callback we can remember the pages any way we want. Right > now in a bitmap. Maybe later in a array + bitmap (as discussed above). > Another idea I had was to simply go over all pages and report them when= > running into this "array full" condition. But I am not yet sure about > the performance implications on rather large machines. So the bitmap > idea might have some other limitations but seems to do its job. That's correct, I was actually trying to come up with a basic framework. Which is acceptable in terms of benefits and performance and that can fit= into most of the use-cases (if not all). After which my plan was to further optimize it. > > Hoe that makes things clearer and am not missing something. Thanks for explaining. > --=20 Thanks Nitesh