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 E637AC352AA for ; Wed, 2 Oct 2019 10:45:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B002F218DE for ; Wed, 2 Oct 2019 10:45:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728021AbfJBKpP convert rfc822-to-8bit (ORCPT ); Wed, 2 Oct 2019 06:45:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34566 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725851AbfJBKpO (ORCPT ); Wed, 2 Oct 2019 06:45:14 -0400 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 8F56D30860BD; Wed, 2 Oct 2019 10:45:13 +0000 (UTC) Received: from [10.40.204.213] (ovpn-204-213.brq.redhat.com [10.40.204.213]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4460E5C226; Wed, 2 Oct 2019 10:44:51 +0000 (UTC) Subject: Re: [PATCH v11 0/6] mm / virtio: Provide support for unused page reporting To: David Hildenbrand , Alexander Duyck Cc: Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm list , "Michael S. Tsirkin" , Dave Hansen , LKML , Matthew Wilcox , Michal Hocko , linux-mm , Andrew Morton , Mel Gorman , Vlastimil Babka , Oscar Salvador , Yang Zhang , Pankaj Gupta , Konrad Rzeszutek Wilk , Rik van Riel , lcapitulino@redhat.com, "Wang, Wei W" , Andrea Arcangeli , Paolo Bonzini , Dan Williams References: <20191001152441.27008.99285.stgit@localhost.localdomain> <7233498c-2f64-d661-4981-707b59c78fd5@redhat.com> <1ea1a4e11617291062db81f65745b9c95fd0bb30.camel@linux.intel.com> <8bd303a6-6e50-b2dc-19ab-4c3f176c4b02@redhat.com> <0603ca4a-d667-f461-4ba7-ff3c0e9fd4df@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: <020ef7af-dae7-4d57-bed8-1ce912d50c1d@redhat.com> Date: Wed, 2 Oct 2019 06:44:48 -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: <0603ca4a-d667-f461-4ba7-ff3c0e9fd4df@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 02 Oct 2019 10:45:13 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/2/19 3:13 AM, David Hildenbrand wrote: > On 02.10.19 02:55, Alexander Duyck wrote: >> On Tue, Oct 1, 2019 at 12:16 PM Nitesh Narayan Lal wrote: >>> >>> On 10/1/19 12:21 PM, Alexander Duyck wrote: >>>> On Tue, 2019-10-01 at 17:35 +0200, David Hildenbrand wrote: >>>>> On 01.10.19 17:29, Alexander Duyck wrote: >>>>>> This series provides an asynchronous means of reporting to a hypervisor >>>>>> that a guest page is no longer in use and can have the data associated >>>>>> with it dropped. To do this I have implemented functionality that allows >>>>>> for what I am referring to as unused page reporting. The advantage of >>>>>> unused page reporting is that we can support a significant amount of >>>>>> memory over-commit with improved performance as we can avoid having to >>>>>> write/read memory from swap as the VM will instead actively participate >>>>>> in freeing unused memory so it doesn't have to be written. >>>>>> >>>>>> The functionality for this is fairly simple. When enabled it will allocate >>>>>> statistics to track the number of reported pages in a given free area. >>>>>> When the number of free pages exceeds this value plus a high water value, >>>>>> currently 32, it will begin performing page reporting which consists of >>>>>> pulling non-reported pages off of the free lists of a given zone and >>>>>> placing them into a scatterlist. The scatterlist is then given to the page >>>>>> reporting device and it will perform the required action to make the pages >>>>>> "reported", in the case of virtio-balloon this results in the pages being >>>>>> madvised as MADV_DONTNEED. After this they are placed back on their >>>>>> original free list. If they are not merged in freeing an additional bit is >>>>>> set indicating that they are a "reported" buddy page instead of a standard >>>>>> buddy page. The cycle then repeats with additional non-reported pages >>>>>> being pulled until the free areas all consist of reported pages. >>>>>> >>>>>> In order to try and keep the time needed to find a non-reported page to >>>>>> a minimum we maintain a "reported_boundary" pointer. This pointer is used >>>>>> by the get_unreported_pages iterator to determine at what point it should >>>>>> resume searching for non-reported pages. In order to guarantee pages do >>>>>> not get past the scan I have modified add_to_free_list_tail so that it >>>>>> will not insert pages behind the reported_boundary. Doing this allows us >>>>>> to keep the overhead to a minimum as re-walking the list without the >>>>>> boundary will result in as much as 18% additional overhead on a 32G VM. >>>>>> >>>>>> >>>> >>>> >>>>>> As far as possible regressions I have focused on cases where performing >>>>>> the hinting would be non-optimal, such as cases where the code isn't >>>>>> needed as memory is not over-committed, or the functionality is not in >>>>>> use. I have been using the will-it-scale/page_fault1 test running with 16 >>>>>> vcpus and have modified it to use Transparent Huge Pages. With this I see >>>>>> almost no difference with the patches applied and the feature disabled. >>>>>> Likewise I see almost no difference with the feature enabled, but the >>>>>> madvise disabled in the hypervisor due to a device being assigned. With >>>>>> the feature fully enabled in both guest and hypervisor I see a regression >>>>>> between -1.86% and -8.84% versus the baseline. I found that most of the >>>>>> overhead was due to the page faulting/zeroing that comes as a result of >>>>>> the pages having been evicted from the guest. >>>>> I think Michal asked for a performance comparison against Nitesh's >>>>> approach, to evaluate if keeping the reported state + tracking inside >>>>> the buddy is really worth it. Do you have any such numbers already? (or >>>>> did my tired eyes miss them in this cover letter? :/) >>>>> >>>> I thought what Michal was asking for was what was the benefit of using the >>>> boundary pointer. I added a bit up above and to the description for patch >>>> 3 as on a 32G VM it adds up to about a 18% difference without factoring in >>>> the page faulting and zeroing logic that occurs when we actually do the >>>> madvise. >>>> >>>> Do we have a working patch set for Nitesh's code? The last time I tried >>>> running his patch set I ran into issues with kernel panics. If we have a >>>> known working/stable patch set I can give it a try. >>> Did you try the v12 patch-set [1]? >>> I remember that you reported the CPU stall issue, which I fixed in the v12. >>> >>> [1] https://lkml.org/lkml/2019/8/12/593 >> So I tried testing with the spin_lock calls replaced with spin_lock >> _irq to resolve the IRQ issue. I also had shuffle enabled in order to >> increase the number of pages being dirtied. >> >> With that setup the bitmap approach is running significantly worse >> then my approach, even with the boundary removed. Since I had to > It would make sense to share the setup+benchmark+performance indication > that you measured. You don't have to share the actual numbers. +1 > >> modify the code to even getting working I am not comfortable posting >> numbers. My suggestion would be to look at reworking the patch set and >> post numbers for my patch set versus the bitmap approach and we can >> look at them then. I would prefer not to spend my time fixing and >> tuning a patch set that I am still not convinced is viable. > I agree, I think Nitesh should work on his patch set and try to > reproduce what you are seeing. Sure. I am always open to suggestions of different benchmarks/setup where I can run my patch-set. > > Also, I think to make a precise statement of "which overhead comes with > external tracking", Nitesh should switch to an approach (motivated by > Michal) like > > 1. Sense lockless if a page is still free > 2. start_isolate_page_range() > -> Failed? Skip > 3. test_pages_isolated() > -> No? undo_isolate_page_range(), skip > 4. Repeat for multiple pages + report > 5. undo_isolate_page_range() > > That is the bare minimum any external tracking will need = some overhead > for the tracking data. As a nice side effect, it get's rid of taking the > zone lock manually AFAIKS. > > But that's unrelated to your series, only to quantify "how much" does > external tracking actually cost. Exactly, first, we need to be sure that the overhead caused by bitmap scanning is not significant. If we are fine with the approach, I will certainly look into this as this would be an excellent enhancement. -- Thanks Nitesh