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=-8.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_NEOMUTT autolearn=unavailable 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 0B485C04E87 for ; Tue, 21 May 2019 12:15:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3A7F217D4 for ; Tue, 21 May 2019 12:15:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728101AbfEUMPr (ORCPT ); Tue, 21 May 2019 08:15:47 -0400 Received: from mail-qt1-f169.google.com ([209.85.160.169]:40207 "EHLO mail-qt1-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726900AbfEUMPq (ORCPT ); Tue, 21 May 2019 08:15:46 -0400 Received: by mail-qt1-f169.google.com with SMTP id k24so20143672qtq.7 for ; Tue, 21 May 2019 05:15:45 -0700 (PDT) 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=m10K91xZiky9XuaFifpls41iCrhL5IxmkHVHI+nmI78=; b=nrGRI0muBly68Mhnj4hPTDHxmwrGQC6oTj/PeGVEBs1zbQySHMi967Cb6Zd9Qb0cEl V8qxFaCKeSNU8Lz7R9slROlHWENGEsOZpR9GxC77UL5S7BpdhzgbCz8cs+wN586k+/vn CYJxKozetGoW4JD4hYIPSYQXUG0fuoSEP7JrEZbcThsqp2bttVq6cWCxEnKaoCHiaEWL FVmP7Hxsemyw7utgixcmOluoiUWVNzR4T13Oz8StNATY8y8XLgSN9+MlAYW9AbN6LtqG Dl3kan1HxISKcfwDm1xRzIEG5GSIAAxPwqNPKfTR6boDKJS3gP8HxlrqDcxufyqT9vz8 XSZw== X-Gm-Message-State: APjAAAUyEmY8oDbuoHoZxUWVbjx7NzG0q0nC16PL5Xn3gv7ke6fFOgZH gSMMnwwvhVTGnC8g+M4JCj8Kyw== X-Google-Smtp-Source: APXvYqxffB5wl3LjQOe5oYpjSlTb9ABOX/Diiui+Kry0FpNN5aC8sXH5lxcJbomIVigpeBr/kw6cLA== X-Received: by 2002:ac8:2de1:: with SMTP id q30mr66863571qta.312.1558440945186; Tue, 21 May 2019 05:15:45 -0700 (PDT) Received: from localhost (nat-pool-brq-t.redhat.com. [213.175.37.10]) by smtp.gmail.com with ESMTPSA id x3sm11330559qtk.75.2019.05.21.05.15.43 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 21 May 2019 05:15:44 -0700 (PDT) Date: Tue, 21 May 2019 14:15:42 +0200 From: Oleksandr Natalenko To: Christian Brauner Cc: Minchan Kim , 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: <20190521121542.3hfvouyynw2haail@butterfly.localdomain> References: <20190520035254.57579-1-minchan@kernel.org> <20190521084158.s5wwjgewexjzrsm6@brauner.io> <20190521110552.GG219653@google.com> <20190521113029.76iopljdicymghvq@brauner.io> <20190521114120.GJ219653@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 21, 2019 at 02:04:00PM +0200, Christian Brauner wrote: > On May 21, 2019 1:41:20 PM GMT+02:00, Minchan Kim wrote: > >On Tue, May 21, 2019 at 01:30:32PM +0200, Christian Brauner wrote: > >> On Tue, May 21, 2019 at 08:05:52PM +0900, Minchan Kim wrote: > >> > On Tue, May 21, 2019 at 10:42:00AM +0200, Christian Brauner wrote: > >> > > 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. > >> > > >> > I don't have any particular preference but just wondering why pidfd > >is > >> > so special to have it as prefix of system call name. > >> > >> It's a whole new API to address processes. We already have > >> clone(CLONE_PIDFD) and pidfd_send_signal() as you have seen since you > >> exported pidfd_to_pid(). And we're going to have pidfd_open(). Your > >> syscall works only with pidfds so it's tied to this api as well so it > >> should follow the naming scheme. This also makes life easier for > >> userspace and is consistent. > > > >Okay. I will change the API name at next revision. > >Thanks. > > Thanks! > Fwiw, there's been a similar patch by Oleksandr for pidfd_madvise I stumbled upon a few days back: > https://gitlab.com/post-factum/pf-kernel/commit/0595f874a53fa898739ac315ddf208554d9dc897 > > He wanted to be cc'ed but I forgot. Thanks :). FWIW, since this submission is essentially a continuation of our discussion involving my earlier KSM submissions here, I won't move my gitlab branch forward and will be happy to assist with what we have here, be it pidfd_madvise() or a set or /proc files (or smth else). > > Christian > -- Best regards, Oleksandr Natalenko (post-factum) Senior Software Maintenance Engineer