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=-0.8 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_SANE_1 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 4F15DC2D0CE for ; Tue, 21 Jan 2020 18:11:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 173C82465B for ; Tue, 21 Jan 2020 18:11:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579630279; bh=njSzAM5BVoktu+NVLcIvRfWaT7QxAsiNOcXypmAdjB0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=zFEo0QHL+nswlgL9ydR77ZxGrxQhuwLDyBQanAHeMOO4B2z4zTlWJoFKMc+bi2DY9 uqG4Ofg673gLDLiM4hIOAEgk/wTdUdRWbjgZY8tHNeDgw8n7ZVD9/fV3ogQznEkhJP kFC+gKeDEYA3G1mRRJymRzl72Gmz3ri5xgROgz88= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729281AbgAUSLS (ORCPT ); Tue, 21 Jan 2020 13:11:18 -0500 Received: from mail-pf1-f196.google.com ([209.85.210.196]:35510 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728186AbgAUSLS (ORCPT ); Tue, 21 Jan 2020 13:11:18 -0500 Received: by mail-pf1-f196.google.com with SMTP id i23so1903852pfo.2; Tue, 21 Jan 2020 10:11:17 -0800 (PST) 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:in-reply-to:user-agent; bh=RZ+UzF1ke9VKh6CSTY/ooI3vzWKiS8jZf7sDVSihHD4=; b=NEFX/ezysY8snsP6VwgBPghhixLPcadjK8oX5390jYlUyypNu5b/NtrWPgM8jPKgKo ZYNjJeCNesZwyzi2bx96bBjOqUOTTlWhBT6lp/fEDzrlq0ifFrL0gfRriLISXIeWkeea PhqMc7Mgk3CT+qm/hbcBoj9YoaFtuOyw26szMr5QS8vSDIROS8D76NvrU2TjDOWbmqWn 0g0CzOvdPkkJlFf29WjCfuofnqqaN0pmSRFeD+8T9Pg2VG0rKrpqmRu/wV5IzMT7+F9U MjcOhkH5b9amo2LQdXTP4KU6jirr+/CWk0FFQAqDuqPvwYGY4LH1aRTPGv0jDDerymb9 2eRA== 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:in-reply-to:user-agent; bh=RZ+UzF1ke9VKh6CSTY/ooI3vzWKiS8jZf7sDVSihHD4=; b=B58Ai3h3GggtlqVAO23HabMO7L/FacK+HJ7I/wyg/0qR2z9flU1y2e1Q7dh2Dj+grW QrNsosw2IVOI15JvB8jBUbGmOgvQMDkYN0JptCNxPB2pEzWEe2ckxpEglg2iY8HfBvRD cyNy4PeaJ77D/MGCK3S7ypIRmuPfE12tUZtLkuYI/RumtLrRQUKMwWV1b+m2jurj0vLe f/0gb5y+hOudlRodfAbt7YrNzpRhprYzLYnKY1xS2X1kKAFJVpfpR8Sr+RwcT9bXZZbT Tzqez/hoDPTrkp3h33HNDMZwQSQtNt70JG6aJEuhXF3mzlhqeZX0MU/8Z8tcEtnMp1Ni EdUA== X-Gm-Message-State: APjAAAUDFOonu/MH7HRlG4BolhpXHWFWQZn+JafVtytZUnBx2LGwV8S8 Vpfxiw29BA+m8XEs77YH/os= X-Google-Smtp-Source: APXvYqwjymOoEv8Ry2p1p8dCMolpdzxYn1+qfp4noIIgwqrM4twhYUXGvrTZzkbYodH1/ny+0fD11g== X-Received: by 2002:aa7:9111:: with SMTP id 17mr5827628pfh.163.1579630277160; Tue, 21 Jan 2020 10:11:17 -0800 (PST) Received: from google.com ([2620:15c:211:1:3e01:2939:5992:52da]) by smtp.gmail.com with ESMTPSA id i11sm122167pjg.0.2020.01.21.10.11.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jan 2020 10:11:15 -0800 (PST) Date: Tue, 21 Jan 2020 10:11:13 -0800 From: Minchan Kim To: "Kirill A. Shutemov" Cc: Michal Hocko , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, oleksandr@redhat.com, Suren Baghdasaryan , Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Johannes Weiner , Shakeel Butt , John Dias , ktkhai@virtuozzo.com, christian.brauner@ubuntu.com, sjpark@amazon.de Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Message-ID: <20200121181113.GE140922@google.com> References: <20200116235953.163318-1-minchan@kernel.org> <20200116235953.163318-3-minchan@kernel.org> <20200117115225.GV19428@dhcp22.suse.cz> <20200117155837.bowyjpndfiym6cgs@box> <20200117173239.GB140922@google.com> <20200117212653.7uftw3lk35oykkmb@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200117212653.7uftw3lk35oykkmb@box> 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 Sat, Jan 18, 2020 at 12:26:53AM +0300, Kirill A. Shutemov wrote: > On Fri, Jan 17, 2020 at 09:32:39AM -0800, Minchan Kim wrote: > > On Fri, Jan 17, 2020 at 06:58:37PM +0300, Kirill A. Shutemov wrote: > > > On Fri, Jan 17, 2020 at 12:52:25PM +0100, Michal Hocko wrote: > > > > On Thu 16-01-20 15:59:50, Minchan Kim wrote: > > > > > There is usecase that System Management Software(SMS) want to give > > > > > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > > > > > in the case of Android, it is the ActivityManagerService. > > > > > > > > > > It's 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 the centralized userspace daemon(ActivityManagerService), > > > > > and that daemon must be able to initiate reclaim on its own without > > > > > any app involvement. > > > > > > > > > > To solve the issue, this patch introduces new syscall process_madvise(2). > > > > > It uses pidfd of an external processs to give the hint. > > > > > > > > > > int process_madvise(int pidfd, void *addr, size_t length, int advise, > > > > > unsigned long flag); > > > > > > > > > > Since it could affect other process's address range, only privileged > > > > > process(CAP_SYS_PTRACE) or something else(e.g., being the same UID) > > > > > gives it the right to ptrace the process could use it successfully. > > > > > The flag argument is reserved for future use if we need to extend the > > > > > API. > > > > > > > > > > I think supporting all hints madvise has/will supported/support to > > > > > process_madvise is rather risky. Because we are not sure all hints make > > > > > sense from external process and implementation for the hint may rely on > > > > > the caller being in the current context so it could be error-prone. > > > > > Thus, I just limited hints as MADV_[COLD|PAGEOUT] in this patch. > > > > > > > > > > If someone want to add other hints, we could hear hear the usecase and > > > > > review it for each hint. It's more safe for maintainace rather than > > > > > introducing a buggy syscall but hard to fix it later. > > > > > > > > I have brought this up when we discussed this in the past but there is > > > > no reflection on that here so let me bring that up again. > > > > > > > > I believe that the interface has an inherent problem that it is racy. > > > > The external entity needs to know the address space layout of the target > > > > process to do anyhing useful on it. The address space is however under > > > > the full control of the target process though and the external entity > > > > has no means to find out that the layout has changed. So > > > > time-to-check-time-to-act is an inherent problem. > > > > > > > > This is a serious design flaw and it should be explained why it doesn't > > > > matter or how to use the interface properly to prevent that problem. > > > > > > I agree, it looks flawed. > > > > > > Also I don't see what System Management Software can generically do on > > > sub-process level. I mean how can it decide which part of address space is > > > less important than other. > > > > > > I see how a manager can indicate that this process (or a group of > > > processes) is less important than other, but on per-addres-range basis? > > > > For example, memory ranges shared by several processes or critical for the > > latency, we could avoid those ranges to be cold/pageout to prevent > > unncecessary CPU burning/paging. > > Hmm.. I still don't see why any external entity has a better (or any) > knowledge about the matter. The process has to do this, no? I think Sandeep already gave enough information in other thread. > > > I also think people don't want to give an KSM hint to non-mergeable area. > > And how the manager knows which data is mergable? Oleksandr, could you say your thought why you need address range based API? > > If you are intimate enough with the process' internal state feel free to > inject syscall into the process with ptrace. Why bother with half-measures? Concern is we want to act the hint in caller's context, not calle because calle is usually very limited in cpuset/cgroups or even freezed state so they couldn't act by themselves quick enough, which makes many problems. One of efforts to solve the issue was "Expedited memory reclaim" https://lwn.net/Articles/785709/ That could be also a good candidate for process_madvise API. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Date: Tue, 21 Jan 2020 10:11:13 -0800 Message-ID: <20200121181113.GE140922@google.com> References: <20200116235953.163318-1-minchan@kernel.org> <20200116235953.163318-3-minchan@kernel.org> <20200117115225.GV19428@dhcp22.suse.cz> <20200117155837.bowyjpndfiym6cgs@box> <20200117173239.GB140922@google.com> <20200117212653.7uftw3lk35oykkmb@box> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200117212653.7uftw3lk35oykkmb@box> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Kirill A. Shutemov" Cc: Michal Hocko , Andrew Morton , LKML , linux-mm , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, oleksandr-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Suren Baghdasaryan , Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Johannes Weiner , Shakeel Butt , John Dias , ktkhai-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org, christian.brauner-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org, sjpark-ebkRAfMGSJGzQB+pC5nmwQ@public.gmane.org List-Id: linux-api@vger.kernel.org On Sat, Jan 18, 2020 at 12:26:53AM +0300, Kirill A. Shutemov wrote: > On Fri, Jan 17, 2020 at 09:32:39AM -0800, Minchan Kim wrote: > > On Fri, Jan 17, 2020 at 06:58:37PM +0300, Kirill A. Shutemov wrote: > > > On Fri, Jan 17, 2020 at 12:52:25PM +0100, Michal Hocko wrote: > > > > On Thu 16-01-20 15:59:50, Minchan Kim wrote: > > > > > There is usecase that System Management Software(SMS) want to give > > > > > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > > > > > in the case of Android, it is the ActivityManagerService. > > > > > > > > > > It's 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 the centralized userspace daemon(ActivityManagerService), > > > > > and that daemon must be able to initiate reclaim on its own without > > > > > any app involvement. > > > > > > > > > > To solve the issue, this patch introduces new syscall process_madvise(2). > > > > > It uses pidfd of an external processs to give the hint. > > > > > > > > > > int process_madvise(int pidfd, void *addr, size_t length, int advise, > > > > > unsigned long flag); > > > > > > > > > > Since it could affect other process's address range, only privileged > > > > > process(CAP_SYS_PTRACE) or something else(e.g., being the same UID) > > > > > gives it the right to ptrace the process could use it successfully. > > > > > The flag argument is reserved for future use if we need to extend the > > > > > API. > > > > > > > > > > I think supporting all hints madvise has/will supported/support to > > > > > process_madvise is rather risky. Because we are not sure all hints make > > > > > sense from external process and implementation for the hint may rely on > > > > > the caller being in the current context so it could be error-prone. > > > > > Thus, I just limited hints as MADV_[COLD|PAGEOUT] in this patch. > > > > > > > > > > If someone want to add other hints, we could hear hear the usecase and > > > > > review it for each hint. It's more safe for maintainace rather than > > > > > introducing a buggy syscall but hard to fix it later. > > > > > > > > I have brought this up when we discussed this in the past but there is > > > > no reflection on that here so let me bring that up again. > > > > > > > > I believe that the interface has an inherent problem that it is racy. > > > > The external entity needs to know the address space layout of the target > > > > process to do anyhing useful on it. The address space is however under > > > > the full control of the target process though and the external entity > > > > has no means to find out that the layout has changed. So > > > > time-to-check-time-to-act is an inherent problem. > > > > > > > > This is a serious design flaw and it should be explained why it doesn't > > > > matter or how to use the interface properly to prevent that problem. > > > > > > I agree, it looks flawed. > > > > > > Also I don't see what System Management Software can generically do on > > > sub-process level. I mean how can it decide which part of address space is > > > less important than other. > > > > > > I see how a manager can indicate that this process (or a group of > > > processes) is less important than other, but on per-addres-range basis? > > > > For example, memory ranges shared by several processes or critical for the > > latency, we could avoid those ranges to be cold/pageout to prevent > > unncecessary CPU burning/paging. > > Hmm.. I still don't see why any external entity has a better (or any) > knowledge about the matter. The process has to do this, no? I think Sandeep already gave enough information in other thread. > > > I also think people don't want to give an KSM hint to non-mergeable area. > > And how the manager knows which data is mergable? Oleksandr, could you say your thought why you need address range based API? > > If you are intimate enough with the process' internal state feel free to > inject syscall into the process with ptrace. Why bother with half-measures? Concern is we want to act the hint in caller's context, not calle because calle is usually very limited in cpuset/cgroups or even freezed state so they couldn't act by themselves quick enough, which makes many problems. One of efforts to solve the issue was "Expedited memory reclaim" https://lwn.net/Articles/785709/ That could be also a good candidate for process_madvise API.