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=-3.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 84F08C3F68F for ; Sat, 18 Jan 2020 09:40:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5124221D7D for ; Sat, 18 Jan 2020 09:40:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="cOPyeCdi" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727107AbgARJku (ORCPT ); Sat, 18 Jan 2020 04:40:50 -0500 Received: from mail-wr1-f68.google.com ([209.85.221.68]:40367 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726602AbgARJkt (ORCPT ); Sat, 18 Jan 2020 04:40:49 -0500 Received: by mail-wr1-f68.google.com with SMTP id c14so24868130wrn.7; Sat, 18 Jan 2020 01:40:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to; bh=uecpYHIlA8EXuE0WlfcP8oL9kLAa1BwGMQHRzItHdQI=; b=cOPyeCdiesvnDtg9QJvwJUPdfpmXUvhjsWG8NAqroLXL+mTRADvlQ9k/k4be0zHSyA iOd4wfzdh5tGfxhEOPc7YQxQ27c3Hm1JbGi2l5EgkXTBIC4M+YDpPfAjgpaN93N+8L02 qCtyyNU0Io4nyp0SMgmE/Ny6nrhyUGoh0f+yc6tl7wdjWhBeojSvjAdHq90KXjZ6Koj+ j2sujyKO0NUEWOXa7nc+PZStuHkMMEtUsgZvQQ2Jb4k9xvMFtGsXLF2xXmxzJhcHSOJ7 g7tE3vxHUzLXUYIXxYem0ZyvnOnLya0T+N8hlPGyus2twVnZTU8RBpW+8HbA4Mln9QAg pyJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to; bh=uecpYHIlA8EXuE0WlfcP8oL9kLAa1BwGMQHRzItHdQI=; b=lJdvbuzjjzhkLQB+M+1+MU7Ekf0xVv1NV1dBbLalSnu7XD/7B8EuxX+ce1QaEDeixm tvwKSo6LZrVk7MsJEW+SFoc1V1X5/Af45NVN/Q8pP41s+il2aHNWrOK0b7Q7rqRgRhkl KO/MaAUCuc8fc9JZi3UNMNEv/ixXU5ThXDHtKGFJDDMF6+ASfq2fx8Qj3BnLFvpX+T+U avZeYqa7rn3Lm1tbEgPjKPCKic+B/gyJLb4yTtLB9us9H87IyVihR0uzks/d+aijobwX bv7Dpw2rVIp56chDoOuVi8ZVSoC1VKI0SnCdHFiIWzExjUjHKgpKn72VVb378phonPFy L+ZQ== X-Gm-Message-State: APjAAAW4tS+Rqy/TWDdhA9RxcnSpXlT24sovlKY72VuqvVRaUtSJrvm1 VU3vyw77dR27fvZOEpyfTPM= X-Google-Smtp-Source: APXvYqwLBqSwG1yBxDMw1A5PEKxZ4fjGJDsR3X4P36SMAVjfbbU0cf6OTOIejp6kPjaKdivMlscJVA== X-Received: by 2002:adf:dfcf:: with SMTP id q15mr7586856wrn.404.1579340447732; Sat, 18 Jan 2020 01:40:47 -0800 (PST) Received: from localhost.localdomain ([2a02:2450:10d2:194d:71c1:e5a:f945:a5c3]) by smtp.gmail.com with ESMTPSA id j12sm38374188wrt.55.2020.01.18.01.40.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Jan 2020 01:40:47 -0800 (PST) From: SeongJae Park To: "Kirill A. Shutemov" Cc: Minchan Kim , 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: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Date: Sat, 18 Jan 2020 10:40:38 +0100 Message-Id: <20200118094038.10507-1-sj38.park@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200117212653.7uftw3lk35oykkmb@box> (raw) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 18 Jan 2020 00:26:53 +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 also think people don't want to give an KSM hint to non-mergeable area. > > And how the manager knows which data is mergable? Couldn't 'idle_page_tracking' like features could be used by the external manager processes to know that? Thanks, SeongJae Park > > 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? > > -- > Kirill A. Shutemov > > From mboxrd@z Thu Jan 1 00:00:00 1970 From: SeongJae Park Subject: Re: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Date: Sat, 18 Jan 2020 10:40:38 +0100 Message-ID: <20200118094038.10507-1-sj38.park@gmail.com> References: <20200117212653.7uftw3lk35oykkmb@box> Return-path: In-Reply-To: <20200117212653.7uftw3lk35oykkmb@box> (raw) Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Kirill A. Shutemov" Cc: Minchan Kim , 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, 18 Jan 2020 00:26:53 +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 also think people don't want to give an KSM hint to non-mergeable area. > > And how the manager knows which data is mergable? Couldn't 'idle_page_tracking' like features could be used by the external manager processes to know that? Thanks, SeongJae Park > > 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? > > -- > Kirill A. Shutemov > >