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=-9.9 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 D0861C33CB1 for ; Sun, 19 Jan 2020 16:14:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E99020678 for ; Sun, 19 Jan 2020 16:14:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="fkp3ivs9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727586AbgASQOi (ORCPT ); Sun, 19 Jan 2020 11:14:38 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:36338 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726860AbgASQOi (ORCPT ); Sun, 19 Jan 2020 11:14:38 -0500 Received: by mail-pg1-f195.google.com with SMTP id k3so14242654pgc.3 for ; Sun, 19 Jan 2020 08:14:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=eTPL0qIft+PAJRKYhuZgerS2zPZNoYqzBPJ/hUNnofk=; b=fkp3ivs9BWu7f2qbRlFnK1Y2IKQewczE/s6Nfs50yHayGYxq851zFjxTBFbFGJj2FR HQf8ve2IM3luGjDGZ7DGUsaP+sfYmRPeA8hiMaYvmcqQgJlCoSKhlZg1ZJEweK1DAQJ8 GAhIyx1FSlk9i4tBIFVrzqgOEJ1JSD+nmRsY2XoValMX5zOQQNyeM7yGEZM/kuLFrNgN VGpnUbaZItCAwZ/jGuXfRx/upOAn30vaA3v2PQWnxCVCKMQjWMzFnW92uQajW/Gv/0cV NyrmZp63Ui5u6X5xAGiSw1qkUbhIABQQd5nqWOjgpNs6xMHwm7ntBfQ4fxfz0SOEjT1i alhQ== 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:in-reply-to:user-agent; bh=eTPL0qIft+PAJRKYhuZgerS2zPZNoYqzBPJ/hUNnofk=; b=LeE6pEjBB3AcB/e/vTxkF3ZAn9Awphu+ZALFuSw2HdAwuh7+yFEFWlwHcwHBzloSVR c7ghvkGsG4dyV90TMkWVFjzIv/frSysMbGUwTTmdGFoxO2D7iE/TvaRGk6nI5U9MeL7E 28G3JdtXHaa6N4tdqTFWbCznIXGd7nfQ83gKabrGl6/QwKorBx16xBrQ69BXjj7ld0iv ed6CxTexxYusp1HhhBoR9/kKa+Tje/QVRKJrGr97mLjC4u4Ow6qzeeYmG/PGGbpdWfwd 167l8kwXjEyUPsP6q8AzLDV0iU/U0egiszEYLRp5/uSdNhCcrg2LJsvAFGjPyKVbyJUq FI+Q== X-Gm-Message-State: APjAAAWWRS4ZaT+mJqRAXhVtdtX29cAHPfwtcQnwkVRll4gvpGvv9S6a i6s4aEImBFbDguelXYN2fCelOg== X-Google-Smtp-Source: APXvYqxiqCVKAw7n8mlcVT4SM73UEmqS8HKyvw+g+QV8PPCiNbHAECRa+6baAKip0NfyEPz+wJGTrw== X-Received: by 2002:a63:4d4c:: with SMTP id n12mr57301291pgl.212.1579450476748; Sun, 19 Jan 2020 08:14:36 -0800 (PST) Received: from sspatil-glaptop2.roam.corp.google.com ([66.167.121.235]) by smtp.gmail.com with ESMTPSA id l2sm14371111pjt.31.2020.01.19.08.14.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 19 Jan 2020 08:14:35 -0800 (PST) Date: Sun, 19 Jan 2020 08:14:31 -0800 From: sspatil@google.com To: kirill@shutemov.name, minchan@kernel.org, mhocko@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, oleksandr@redhat.com, surenb@google.com, timmurray@google.com, dancol@google.com, sonnyrao@google.com, bgeffon@google.com, hannes@cmpxchg.org, shakeelb@google.com, joaodias@google.com, ktkhai@virtuozzo.com, christian.brauner@ubuntu.com, sjpark@amazon.de Cc: Minchan Kim , Michal Hocko , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, oleksandr@redhat.com, Suren Baghdasaryan , Tim Murray , Daniel Colascione , 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: <20200119161431.GA94410@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? FWIW, I totally agree with the time-to-check-time-to-react problem. However, I'd like to clarify the ActivityManager/SystemServer case (I'll call it SystemServer from now on) For Android, every application (including the special SystemServer) are forked from Zygote. The reason ofcourse is to share as many libraries and classes between the two as possible to benefit from the preloading during boot. After applications start, (almost) all of the APIs end up calling into this SystemServer process over IPC (binder) and back to the application. In a fully running system, the SystemServer monitors every single process periodically to calculate their PSS / RSS and also decides which process is "important" to the user for interactivity. So, because of how these processes start _and_ the fact that the SystemServer is looping to monitor each process, it does tend to *know* which address range of the application is not used / useful. Besides, we can never rely on applications to clean things up themselves. We've had the "hey app1, the system is low on memory, please trim your memory usage down" notifications for a long time[1]. They rely on applications honoring the broadcasts and very few do. So, if we want to avoid the inevitable killing of the application and restarting it, some way to be able to tell the OS about unimportant memory in these applications will be useful. - ssp 1. https://developer.android.com/topic/performance/memory > > > 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? > > 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: sspatil-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API Date: Sun, 19 Jan 2020 08:14:31 -0800 Message-ID: <20200119161431.GA94410@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-oKw7cIdHH8eLwutG50LtGA@public.gmane.org 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 , 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? FWIW, I totally agree with the time-to-check-time-to-react problem. However, I'd like to clarify the ActivityManager/SystemServer case (I'll call it SystemServer from now on) For Android, every application (including the special SystemServer) are forked from Zygote. The reason ofcourse is to share as many libraries and classes between the two as possible to benefit from the preloading during boot. After applications start, (almost) all of the APIs end up calling into this SystemServer process over IPC (binder) and back to the application. In a fully running system, the SystemServer monitors every single process periodically to calculate their PSS / RSS and also decides which process is "important" to the user for interactivity. So, because of how these processes start _and_ the fact that the SystemServer is looping to monitor each process, it does tend to *know* which address range of the application is not used / useful. Besides, we can never rely on applications to clean things up themselves. We've had the "hey app1, the system is low on memory, please trim your memory usage down" notifications for a long time[1]. They rely on applications honoring the broadcasts and very few do. So, if we want to avoid the inevitable killing of the application and restarting it, some way to be able to tell the OS about unimportant memory in these applications will be useful. - ssp 1. https://developer.android.com/topic/performance/memory > > > 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? > > 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