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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E910AC433EF for ; Mon, 10 Jan 2022 15:22:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 45FDD6B0073; Mon, 10 Jan 2022 10:22:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4355F6B0074; Mon, 10 Jan 2022 10:22:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 324ED6B0075; Mon, 10 Jan 2022 10:22:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0117.hostedemail.com [216.40.44.117]) by kanga.kvack.org (Postfix) with ESMTP id 22A396B0073 for ; Mon, 10 Jan 2022 10:22:00 -0500 (EST) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id DBCC7181CB2CA for ; Mon, 10 Jan 2022 15:21:59 +0000 (UTC) X-FDA: 79014742758.22.18665E5 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf16.hostedemail.com (Postfix) with ESMTP id B52F018002E for ; Mon, 10 Jan 2022 15:21:56 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 4ABDB1F383; Mon, 10 Jan 2022 15:21:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1641828115; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qpTQmsspjI0q4mx2a8NrDJzrYQO5hqA3JJyE7DUO7w4=; b=Hk+f4nabnmeaiBbecxvUQ4Nmy+Uhh4ATDM6RvYRe7hK9hNq1S6kXXWWap4j4YzaiczcsM9 YkhRVBMw3/8j/WBv637mZBeg+c+ttp9boV06pnUZDE01Kn+m4RE5Cj88LFEdZUyqRyiyDu +zZDdBtusPwzUPsvl75R/mnJfRw11aw= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 56BCFA3B83; Mon, 10 Jan 2022 15:21:54 +0000 (UTC) Date: Mon, 10 Jan 2022 16:21:53 +0100 From: Michal Hocko To: Yu Zhao 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: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B52F018002E X-Stat-Signature: 58oqgohzb1heg9gcrwp7cstatsg15ot6 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=Hk+f4nab; spf=pass (imf16.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-HE-Tag: 1641828116-366918 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 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. > 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. -- Michal Hocko SUSE Labs