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=1.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_MUTT autolearn=no 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 1F698C04AAF for ; Tue, 21 May 2019 11:06:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D86F521773 for ; Tue, 21 May 2019 11:06:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558436762; bh=DPeYcIC286c4DTau4qykbZrwPhQCoU3ZcbeoTpirlE0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=uK6pWRmUXBz1ngcX+QflbZYubdLVaOwzg6bYzAWoHoZs1eFON/hTpuLuCda9UwK8J RXpPM6uoPQFR88g67v1LoOKA+tbpU7pTcgcmA9eUouQtFEJ7lMPf+ALyZZIqfvL71g 4dIoK7azpVRwagB/7cqiLY5Q0I6BmpVvPOubGbBA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727659AbfEULGA (ORCPT ); Tue, 21 May 2019 07:06:00 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:38349 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726242AbfEULGA (ORCPT ); Tue, 21 May 2019 07:06:00 -0400 Received: by mail-pg1-f195.google.com with SMTP id j26so8423969pgl.5 for ; Tue, 21 May 2019 04:05:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=KOZb8yQcjy+VjCqxduvm6OD6AUx3NXKhaQcxseL+T4k=; b=CA08YdMIhOU/VrYm5k9zPXXxOIVVirvReQ8Y2vIbgjyvR/my+aC7evfjsYLMswEKYu 2WAIX7SPn9ewBv3dRf5ErbnWeoH3xnY9J8WBoppqqmKLckLRXJgjedKaZkx8GNdOUFQU dDtuCcAcSjT/ENaln53Wnl7gArCEAukOPQ5ksWGjz8LdjWv9eLudbpaBY1RHZ47ZY0jD lr5tYJNYv77s6nCydHZUSzJAvSZftVRePPQnEgENa+BRrGzYNVdqv78HJd97q5qtcmSF K3cjY0TWfVcUl0KewMvxp6yT85emXsT3Ydg4x3M0GvNpBMbIGCwl/a1huFd0FZFA+p6m +pUg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition :content-transfer-encoding:in-reply-to:user-agent; bh=KOZb8yQcjy+VjCqxduvm6OD6AUx3NXKhaQcxseL+T4k=; b=iLvyp/CY3mD8IN9KTG8JzNnF9XAFaFvs9332nARsRvoqNVjGrlrmF2AUC3LO3kRJbG LRD42IDljhCUDFVgEWd5ZrP6HglbucIVV5KFZvE4gFchu9m/o23cJfTi/926gsWpBh7N Ju0WteOwywGBA3dkvt79iIX5emyqnkAbhT7C0g8SlRhVNRx6zJafpMQUYS/+MyQbJIiL pjjA9ueHPjQb5WX5au1COMo7SHZtQ6BwZPIywR85CCklAk4n+6FTKm4EIjUb7JAEjPER NCXtymt/aP+rTNjsbGq1XWY601EbR3w9DXjzSTz16CK5ag6t5fT5itWsN+TL/deQCXJZ VI4w== X-Gm-Message-State: APjAAAVJDmBsSKJTccX/2dBd1+OLrsMxrT2nsTokON+Ai6hRiai/4v+6 y2Oiis3CvSza5QvIElVC3kU= X-Google-Smtp-Source: APXvYqxlqlFPB+NUCI72RbnbT2TM6iFMigkYLu0cELmj7et0/QOSGQxsMk8DSdijr03Yep9LS5ijzw== X-Received: by 2002:a62:87c6:: with SMTP id i189mr88245711pfe.65.1558436759441; Tue, 21 May 2019 04:05:59 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id x7sm15581305pfm.82.2019.05.21.04.05.55 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 21 May 2019 04:05:58 -0700 (PDT) Date: Tue, 21 May 2019 20:05:52 +0900 From: Minchan Kim To: Christian Brauner 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: <20190521110552.GG219653@google.com> References: <20190520035254.57579-1-minchan@kernel.org> <20190521084158.s5wwjgewexjzrsm6@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190521084158.s5wwjgewexjzrsm6@brauner.io> 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 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. > > 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. Sure!