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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 DB554ECE587 for ; Tue, 1 Oct 2019 16:21:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A1A8221A4C for ; Tue, 1 Oct 2019 16:21:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1A8221A4C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 507D68E0007; Tue, 1 Oct 2019 12:21:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 492288E0001; Tue, 1 Oct 2019 12:21:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 358D38E0007; Tue, 1 Oct 2019 12:21:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0217.hostedemail.com [216.40.44.217]) by kanga.kvack.org (Postfix) with ESMTP id 0B2978E0001 for ; Tue, 1 Oct 2019 12:21:50 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id B15768243763 for ; Tue, 1 Oct 2019 16:21:49 +0000 (UTC) X-FDA: 75995731938.13.beast79_8446f9abc4029 X-HE-Tag: beast79_8446f9abc4029 X-Filterd-Recvd-Size: 5922 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Tue, 1 Oct 2019 16:21:48 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Oct 2019 09:21:46 -0700 X-IronPort-AV: E=Sophos;i="5.64,571,1559545200"; d="scan'208";a="181738489" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Oct 2019 09:21:46 -0700 Message-ID: <1ea1a4e11617291062db81f65745b9c95fd0bb30.camel@linux.intel.com> Subject: Re: [PATCH v11 0/6] mm / virtio: Provide support for unused page reporting From: Alexander Duyck To: David Hildenbrand , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, mst@redhat.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, osalvador@suse.de Cc: yang.zhang.wz@gmail.com, pagupta@redhat.com, konrad.wilk@oracle.com, nitesh@redhat.com, riel@surriel.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com Date: Tue, 01 Oct 2019 09:21:46 -0700 In-Reply-To: <7233498c-2f64-d661-4981-707b59c78fd5@redhat.com> References: <20191001152441.27008.99285.stgit@localhost.localdomain> <7233498c-2f64-d661-4981-707b59c78fd5@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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 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. - Alex