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=-2.2 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 A26ACC432C2 for ; Tue, 24 Sep 2019 15:52:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5B04B214AF for ; Tue, 24 Sep 2019 15:52:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5B04B214AF 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 E5B046B0005; Tue, 24 Sep 2019 11:52:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E0B886B0006; 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Tue, 24 Sep 2019 15:51:59 +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 47787600CC; Tue, 24 Sep 2019 15:51:43 +0000 (UTC) Subject: Re: [PATCH v10 0/6] mm / virtio: Provide support for unused page reporting To: David Hildenbrand , Michal Hocko , Alexander Duyck Cc: 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, linux-mm@kvack.org, vbabka@suse.cz, akpm@linux-foundation.org, mgorman@techsingularity.net, linux-arm-kernel@lists.infradead.org, osalvador@suse.de, yang.zhang.wz@gmail.com, pagupta@redhat.com, konrad.wilk@oracle.com, riel@surriel.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com References: <20190918175109.23474.67039.stgit@localhost.localdomain> <20190924142342.GX23050@dhcp22.suse.cz> From: Nitesh Narayan Lal Openpgp: preference=signencrypt Autocrypt: addr=nitesh@redhat.com; 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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 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.63]); Tue, 24 Sep 2019 15:51:59 +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 9/24/19 11:32 AM, David Hildenbrand wrote: > On 24.09.19 16:23, Michal Hocko wrote: >> On Wed 18-09-19 10:52:25, Alexander Duyck wrote: >> [...] >>> 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 sh= ould >>> 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 i= t >>> will not insert pages behind the reported_boundary. >>> >>> If another process needs to perform a massive manipulation of the fre= e >>> list, such as compaction, it can either reset a given individual boun= dary >>> which will push the boundary back to the list_head, or it can clear t= he >>> bit indicating the zone is actively processing which will result in t= he >>> reporting process resetting all of the boundaries for a given zone. >> Is this any different from the previous version? The last review >> feedback (both from me and Mel) was that we are not happy to have an >> externally imposed constrains on how the page allocator is supposed to= >> maintain its free lists. >> >> If this is really the only way to go forward then I would like to hear= >> very convincing arguments about other approaches not being feasible. > Adding to what Alexander said, I don't consider the other approaches > (especially the bitmap-based approach Nitesh is currently working on) > infeasible. There might be more rough edges (e.g., sparse zones) and > eventually sometimes a little more work to be done, but definitely > feasible. Incorporating stuff into the buddy might make some tasks > (e.g., identify free pages) more efficient. My plan was to get a framework ready which can perform decently and is acceptable upstream (keeping core-mm changes to a minimum) and then ke= ep optimizing it for different use-cases. Indeed, the bitmap-based approach may not be efficient for every availabl= e use case. But then I am not sure if we want to target that, considering it ma= y require mm-changes. > I still somewhat like the idea of capturing hints of free pages (in > whatever data structure) and then going over the hints, seeing if the > pages are still free. Then only temporarily isolating the still-free > pages, reporting them, and un-isolating them after they were reported. = I > like the idea that the pages are not fake-allocated but only temporaril= y > blocked. That works nicely e.g., with the movable zone (contain only > movable data). > > But anyhow, after decades of people working on free page > hinting/reporting, I am happy with anything that gets accepted upstream= :D +1 > --=20 Nitesh