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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 3AE41C31E5E for ; Wed, 19 Jun 2019 12:27:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0A7A521873 for ; Wed, 19 Jun 2019 12:27:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560947276; bh=gLkdy1d4kEKGgOnzOEe1UvPWgSeem7EjkULccV84xEA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rXp0kufDK1eMt1hiRhJnndqcZwwAzN1nbhVTdmaA98PPRfAYpnazIlp//GPVGh5RQ T/wbvNB7kXF3yyzD7M29+fXnA7qPbkU5K5SWrz59KrsmkHqJ0iEwGSF/3+6Pg+zI0Z 4j5J6uQzWfAzct+ChRCyS+EThgey4vkJ/PcOmYd8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731715AbfFSM1y (ORCPT ); Wed, 19 Jun 2019 08:27:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:49118 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727068AbfFSM1y (ORCPT ); Wed, 19 Jun 2019 08:27:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id DC7A6AD3B; Wed, 19 Jun 2019 12:27:51 +0000 (UTC) Date: Wed, 19 Jun 2019 14:27:50 +0200 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , linux-api@vger.kernel.org, Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , jannh@google.com, oleg@redhat.com, christian@brauner.io, oleksandr@redhat.com, hdanton@sina.com, lizeb@google.com Subject: Re: [PATCH v2 0/5] Introduce MADV_COLD and MADV_PAGEOUT Message-ID: <20190619122750.GN2968@dhcp22.suse.cz> References: <20190610111252.239156-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190610111252.239156-1-minchan@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 10-06-19 20:12:47, Minchan Kim wrote: > This patch is part of previous series: > https://lore.kernel.org/lkml/20190531064313.193437-1-minchan@kernel.org/T/#u > Originally, it was created for external madvise hinting feature. > > https://lkml.org/lkml/2019/5/31/463 > Michal wanted to separte the discussion from external hinting interface > so this patchset includes only first part of my entire patchset > > - introduce MADV_COLD and MADV_PAGEOUT hint to madvise. > > However, I keep entire description for others for easier understanding > why this kinds of hint was born. > > Thanks. > > This patchset is against on next-20190530. > > Below is description of previous entire patchset. > ================= &< ===================== > > - 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. > > To achieve the goal, the patchset introduce two new options for madvise. > One is MADV_COLD which will deactivate activated pages and the other is > MADV_PAGEOUT 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_PAGEOUT 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_COLD 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 all is a very good background information suitable for the cover letter. > 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; /* the size of this structure */ > int cookie; /* reserved to support atomicity */ > int nr_elem; /* count of below arrary fields */ > int __user *hints; /* hints for each range */ > /* to store result of each operation */ > const struct iovec __user *results; > /* input address ranges */ > const struct iovec __user *ranges; > }; > > int process_madvise(int pidfd, struct pr_madvise_param *u_param, > unsigned long flags); But this and the following paragraphs are referring to the later step when the madvise gains a remote process capabilities and that is out of the scope of this patch series so I would simply remove it from here. Andrew tends to put the cover letter into the first patch of the series and that would be indeed confusing here. -- Michal Hocko SUSE Labs