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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3FB7DC4332F for ; Wed, 12 Jan 2022 08:08:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351426AbiALIIU (ORCPT ); Wed, 12 Jan 2022 03:08:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351416AbiALIIU (ORCPT ); Wed, 12 Jan 2022 03:08:20 -0500 Received: from mail-io1-xd32.google.com (mail-io1-xd32.google.com [IPv6:2607:f8b0:4864:20::d32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F957C06173F for ; Wed, 12 Jan 2022 00:08:20 -0800 (PST) Received: by mail-io1-xd32.google.com with SMTP id o7so2459377ioo.9 for ; Wed, 12 Jan 2022 00:08:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=WFX0A5hPtLq2y+4vv8Glr1WeFBcLpToPaecrV540Urk=; b=OBoRktJAv2XSBOFIYv6FTRsogQts1376KLhe7+5DMuFh7zRq5yAzGpqqXyDHj9Xjlb zotg52mPLRjGo6JHqs8a8N3MNFQXCWj/igX/71yKCdvHpQKVu0yd31fWY1gSFmUlwJ6X ZMSVBsO2CuLPHnyELp6xcWP2DErwfVG70j4xM2qnfBrXMI1aRbbazUqGDTiqtRrpqTbZ 9xV45uFJmSmfaJmdQKyEP3ks97tS5WK6/jLQ+x9FEdirZ2JWpo0rTci8disi/gFeyrJf CPpop5aA7QFRTB9cPJm4sFRxoK1R67hphj6jIur2TBzKWeY8Gj0aZAFIrw6WPXx6O3z5 WdwA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=WFX0A5hPtLq2y+4vv8Glr1WeFBcLpToPaecrV540Urk=; b=JOhxKU735Q5JioDhLC6kV6r3NtZJf1+6k6Tw/LccoxbgdpuncVRKANHtQkyJ4gHO9T jHZL2Ol9Jio+ZUBsWVYCdnjEd/aUBrPEsXJ7hqPNlgfWAoFuAtkEl6UKoe6b9g9LQrkn QdozvZoPYQ9kNqRBdwNjhtQ/YdEzAYCb/G5J/W4UFpsa7+ADTCw2IyJzTQovt4YvAxM+ cI3ibvA9oo+elJg2RiBPYr6snV/1KMDnG6sljctoxbLHvFhL4sAOOr4jz0LTqfmU8kCl 0K3iDw7aVJ8/LbI30b8Fx4zJrvwZyGWX5DsYNmjK3KphTUUALlYjrbzK9/BNJ0lSDZyt R4Xw== X-Gm-Message-State: AOAM530gf7sdc2fhK4o01J/iviZGbpqDgR4qNv59GB6UJdejOfK6JR/u DgApG1DJZ9xslGANaH9DWfiwkw== X-Google-Smtp-Source: ABdhPJxO3An+3xlKK9bsJDfMFJ5VcX2bkSlQ27yXvyOjxBnpGUi93F7uIIXHnwXvCww63eGPNQJTkQ== X-Received: by 2002:a05:6638:35a3:: with SMTP id v35mr3884475jal.137.1641974899399; Wed, 12 Jan 2022 00:08:19 -0800 (PST) Received: from google.com ([2620:15c:183:200:b6b6:70f4:b540:6383]) by smtp.gmail.com with ESMTPSA id d11sm7352276ilv.6.2022.01.12.00.08.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Jan 2022 00:08:18 -0800 (PST) Date: Wed, 12 Jan 2022 01:08:14 -0700 From: Yu Zhao To: Michal Hocko Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Konstantin Kharlamov Subject: Re: [PATCH v6 5/9] mm: multigenerational lru: mm_struct list Message-ID: References: <20220104202227.2903605-1-yuzhao@google.com> <20220104202227.2903605-6-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, Jan 10, 2022 at 04:21:53PM +0100, Michal Hocko wrote: > On Fri 07-01-22 17:19:28, Yu Zhao wrote: > > On Fri, Jan 07, 2022 at 10:06:15AM +0100, Michal Hocko wrote: > > > On Tue 04-01-22 13:22:24, Yu Zhao wrote: > > > > To exploit spatial locality, the aging prefers to walk page tables to > > > > search for young PTEs. And this patch paves the way for that. > > > > > > > > An mm_struct list is maintained for each memcg, and an mm_struct > > > > follows its owner task to the new memcg when this task is migrated. > > > > > > How does this work actually for the memcg reclaim? I can see you > > > lru_gen_migrate_mm on the task migration. My concern is, though, that > > > such a task leaves all the memory behind in the previous memcg (in > > > cgroup v2, in v1 you can opt in for charge migration). If you move the > > > mm to a new memcg then you age it somewhere where the memory is not > > > really consumed. > > > > There are two options to gather the accessed bit: page table walks and > > rmap walks. Page table walks sweep dense hotspots that are NOT > > misplaced in terms of reclaim scope (lruvec); rmap walks cover what > > page table walks miss, e.g., misplaced dense hotspots or sparse ones. > > > > Dense hotspots are stored in Bloom filters for each lruvec. > > > > If an mm leaves everything in the old memcg, page table walks in the > > new memcg reclaim path basically ignore this mm after the first scan, > > because everything is misplaced. > > OK, so do I get it right that pages mapped from a different memcg than > the reclaimed one are considered effectivelly non-present from the the > reclaim logic POV? This would be worth mentioning in the migration > callback because it is not really that straightforward to put those two > together. That's correct. Will document this in detail. > > In the old memcg reclaim path, page table walks won't see this mm > > at all. But rmap walks will catch everything later in the eviction > > path, i.e., lru_gen_look_around(). This function is less efficient > > compared with page table walks because, for each rmap walk of a > > non-shared page, it only can gather the accessed bit from 64 PTEs at > > most. But it's still a lot faster than the original rmap, which only > > gathers the accessed bit from a single PTE, for each walk of a > > non-shared page. > > Again, something that should be really documented. Noted.