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=-3.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham 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 6AE5BC46470 for ; Tue, 21 May 2019 08:42:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F69D2173E for ; Tue, 21 May 2019 08:42:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=brauner.io header.i=@brauner.io header.b="Ofc5UreW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726870AbfEUImM (ORCPT ); Tue, 21 May 2019 04:42:12 -0400 Received: from mail-pg1-f169.google.com ([209.85.215.169]:41661 "EHLO mail-pg1-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726692AbfEUImL (ORCPT ); Tue, 21 May 2019 04:42:11 -0400 Received: by mail-pg1-f169.google.com with SMTP id z3so8223512pgp.8 for ; Tue, 21 May 2019 01:42:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brauner.io; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=fL2NycB/KBQwPHhyJm1TK8C2/P0KHX/e0jDcXqFMlXc=; b=Ofc5UreWBIBCwYkWRg3poRUI0RkUh9zFBpFMazgql8Eq4K1AQwC3CW/BRmyWVuy0If YpEU0indo2hVEy2p9tQt41yJd8MeelgTKIKvs2GoTsdkYbv7gxouQNWTIfwp3tOgXUlu iuMaEKsrvBdtucpuEY3mT1E/ZeFBu0mxEjZqm52eTdMw7Whna4qSRai1H9XdiJNksog2 53RR3LtYGEM8Xu48PvnIssFyeA9DdiyZWxbH+KTps4uyqrBEV1CD/et0r4BUmSxaYAqs yisSFZbWlIlvop0smOgfEZNwu/TkfqC2sReITQYQwNuzRu/w7pFK1n3q/KjMUCopC4/L KydA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=fL2NycB/KBQwPHhyJm1TK8C2/P0KHX/e0jDcXqFMlXc=; b=G0ixmv1s+1kifolC/J8KLid8ImGydY/aTkFsmjQq1tBJ7koiLaAq3Pjm106xPQcGnQ 2wVwfOtbQjM59HGWRpXsoMhv4xVL7KC/xJVzEDhNdsF0zsD0JT7R5QwNzjgxw/fE+o2b 0Pfqgm1vNRu8MUO7nvjHnxu/kEmYmIPOt99eGRsld3bDcik5kPyy/s1kRyqCP8bCvK1Y eWQJG0g01Tpte9JzHbe6NrDqEnjMjftoh6IPk9MO4J08zpr9q+zg4msZ4zoOAbGbpBeC lY6WF+jm0wl2nXhDwAp4oKdUQVHXLJZf2Vu8bmy3TsR6vQfWCtFVLfF9fPIiVO6oflSr S27A== X-Gm-Message-State: APjAAAXjbbxm6UUhWoVeqi3hUUYostJETt9WfHQ6YQJYGU9vS4GaQhEq 2Lu3ojDwgSPmRUzY9rNC+8pwsA== X-Google-Smtp-Source: APXvYqynUeUEzy72MP695EG5nsL6QCyxNd0eoISiaP6I/i+P560cW2wcRGnBreJqNUFhz98ZKE/JJA== X-Received: by 2002:a63:ed16:: with SMTP id d22mr79872044pgi.35.1558428130440; Tue, 21 May 2019 01:42:10 -0700 (PDT) Received: from brauner.io ([208.54.39.182]) by smtp.gmail.com with ESMTPSA id u11sm21973817pfh.130.2019.05.21.01.42.04 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 21 May 2019 01:42:09 -0700 (PDT) Date: Tue, 21 May 2019 10:42:00 +0200 From: Christian Brauner To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Michal Hocko , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , jannh@google.com Subject: Re: [RFC 0/7] introduce memory hinting API for external process Message-ID: <20190521084158.s5wwjgewexjzrsm6@brauner.io> References: <20190520035254.57579-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190520035254.57579-1-minchan@kernel.org> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote: > - Background > > The Android terminology used for forking a new process and starting an app > from scratch is a cold start, while resuming an existing app is a hot start. > While we continually try to improve the performance of cold starts, hot > starts will always be significantly less power hungry as well as faster so > we are trying to make hot start more likely than cold start. > > To increase hot start, Android userspace manages the order that apps should > be killed in a process called ActivityManagerService. ActivityManagerService > tracks every Android app or service that the user could be interacting with > at any time and translates that into a ranked list for lmkd(low memory > killer daemon). They are likely to be killed by lmkd if the system has to > reclaim memory. In that sense they are similar to entries in any other cache. > Those apps are kept alive for opportunistic performance improvements but > those performance improvements will vary based on the memory requirements of > individual workloads. > > - Problem > > Naturally, cached apps were dominant consumers of memory on the system. > However, they were not significant consumers of swap even though they are > good candidate for swap. Under investigation, swapping out only begins > once the low zone watermark is hit and kswapd wakes up, but the overall > allocation rate in the system might trip lmkd thresholds and cause a cached > process to be killed(we measured performance swapping out vs. zapping the > memory by killing a process. Unsurprisingly, zapping is 10x times faster > even though we use zram which is much faster than real storage) so kill > from lmkd will often satisfy the high zone watermark, resulting in very > few pages actually being moved to swap. > > - Approach > > The approach we chose was to use a new interface to allow userspace to > proactively reclaim entire processes by leveraging platform information. > This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages > that are known to be cold from userspace and to avoid races with lmkd > by reclaiming apps as soon as they entered the cached state. Additionally, > it could provide many chances for platform to use much information to > optimize memory efficiency. > > IMHO we should spell it out that this patchset complements MADV_WONTNEED > and MADV_FREE by adding non-destructive ways to gain some free memory > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > when memory pressure rises. > > To achieve the goal, the patchset introduce two new options for madvise. > One is MADV_COOL which will deactive activated pages and the other is > MADV_COLD which will reclaim private pages instantly. These new options > complement MADV_DONTNEED and MADV_FREE by adding non-destructive ways to > gain some free memory space. MADV_COLD is similar to MADV_DONTNEED in a way > that it hints the kernel that memory region is not currently needed and > should be reclaimed immediately; MADV_COOL is similar to MADV_FREE in a way > that it hints the kernel that memory region is not currently needed and > should be reclaimed when memory pressure rises. > > This approach is similar in spirit to madvise(MADV_WONTNEED), but the > information required to make the reclaim decision is not known to the app. > Instead, it is known to a centralized userspace daemon, and that daemon > must be able to initiate reclaim on its own without any app involvement. > To solve the concern, this patch introduces new syscall - > > struct pr_madvise_param { > int size; > const struct iovec *vec; > } > > int process_madvise(int pidfd, ssize_t nr_elem, int *behavior, > struct pr_madvise_param *restuls, > struct pr_madvise_param *ranges, > unsigned long flags); > > The syscall get pidfd to give hints to external process and provides > pair of result/ranges vector arguments so that it could give several > hints to each address range all at once. > > I guess others have different ideas about the naming of syscall and options > so feel free to suggest better naming. Yes, all new syscalls making use of pidfds should be named pidfd_. So please make this pidfd_madvise. Please make sure to Cc me on this in the future as I'm maintaining pidfds. Would be great to have Jann on this too since he's been touching both mm and parts of the pidfd stuff with me.