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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 515A0C432BE for ; Tue, 3 Aug 2021 17:28:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3383460E78 for ; Tue, 3 Aug 2021 17:28:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238213AbhHCR2K (ORCPT ); Tue, 3 Aug 2021 13:28:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237938AbhHCR2J (ORCPT ); Tue, 3 Aug 2021 13:28:09 -0400 Received: from mail-yb1-xb2f.google.com (mail-yb1-xb2f.google.com [IPv6:2607:f8b0:4864:20::b2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4C9FC061757 for ; Tue, 3 Aug 2021 10:27:57 -0700 (PDT) Received: by mail-yb1-xb2f.google.com with SMTP id p145so20393864ybg.6 for ; Tue, 03 Aug 2021 10:27:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=tTZ5g4GTILsDQHp1eqPRFqPGKzM3iGG8XzvZFkbQn5Q=; b=Q2WtkHAqT08j9j6JZNFmzJDazhybSJWhcsPGUi93jChlAh7Ooo/2WM/Wagoul/9Nl0 Y+kU5GD/nFBQ4T5SPxSvqmnXMmhvTTp3EaP3e89PAQkKwV66ajjGdizUmux4142dQqxR BU7E0KbviB2lKuItNBO9ITKSEBuNXA0f83J07AJxgGXFXVDQ2FeES+ydhEnE67NdTR48 iMe8SZwe0c0Wc6RFTlxHCS7TCO/IvG07Npz0znwrjnhhxsHhZxUdaNROpbTbkmjKhAk8 lGcptZtMb69rNGTYsyY7wEdqJf/qcrp+gRRGAL9+aMIrACMSwlbky78bIaiDZj9BMG48 4ycg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=tTZ5g4GTILsDQHp1eqPRFqPGKzM3iGG8XzvZFkbQn5Q=; b=dd0pNOe32TfE4vTHjq9+OMDno/v5KX2dkdF2hM2abT6YMR4+cU75VCdFPeTYTsfDqn ppDwe9Uz4CSoLf1Z4yph1IjtXYqI24vv/k4nuX/uHPWj4Z3ZHGcm7fhNSj/XfXJqjViS OrBOmM1sfyiwtGSPkbQnGkMZV80jL8MLweng2QYihAlzDhET6qRVNTS+f5AQL+iCCZp5 uq3R4KOZmV8WukSCqCUbO3KL1/R44DptFMDekf9Lbt+MbMRinJWtdrQMg5kV7KClMAR3 CTeljiBdzOMyob6mh0DV06HO0j9nu9H5guGPV5gWjQGIM59rWiE68KQLYfLl1J+hV5id seLQ== X-Gm-Message-State: AOAM532cIdgW+E9QHltXxhYr+H4KFZZB28CoeyvNlzP1otcmKbPE5OQ7 kONn09JeXQPaI6WLp0vrGYVOlroMgI+6LA+wd3+q7g== X-Google-Smtp-Source: ABdhPJzQyiU4rreG5VZBo/3+o/Cqn4zQ4RIZdZLrfNJKLQ/gBgJysO57Kkp1iRQQ1WakNnYBMblrGG3vb9gVi120A4w= X-Received: by 2002:a25:bc2:: with SMTP id 185mr28865645ybl.23.1628011676754; Tue, 03 Aug 2021 10:27:56 -0700 (PDT) MIME-Version: 1.0 References: <20210802221431.2251210-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 3 Aug 2021 10:27:45 -0700 Message-ID: Subject: Re: [PATCH v4 1/2] mm: introduce process_mrelease system call To: Michal Hocko Cc: Andrew Morton , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Minchan Kim , Christian Brauner , Christoph Hellwig , Oleg Nesterov , David Hildenbrand , Jann Horn , Shakeel Butt , Andy Lutomirski , Christian Brauner , Florian Weimer , Jan Engelhardt , Tim Murray , Linux API , linux-mm , LKML , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 3, 2021 at 1:39 AM Michal Hocko wrote: > > On Mon 02-08-21 15:14:30, Suren Baghdasaryan wrote: > > In modern systems it's not unusual to have a system component monitoring > > memory conditions of the system and tasked with keeping system memory > > pressure under control. One way to accomplish that is to kill > > non-essential processes to free up memory for more important ones. > > Examples of this are Facebook's OOM killer daemon called oomd and > > Android's low memory killer daemon called lmkd. > > For such system component it's important to be able to free memory > > quickly and efficiently. Unfortunately the time process takes to free > > up its memory after receiving a SIGKILL might vary based on the state > > of the process (uninterruptible sleep), size and OPP level of the core > > the process is running. A mechanism to free resources of the target > > process in a more predictable way would improve system's ability to > > control its memory pressure. > > Introduce process_mrelease system call that releases memory of a dying > > process from the context of the caller. This way the memory is freed in > > a more controllable way with CPU affinity and priority of the caller. > > The workload of freeing the memory will also be charged to the caller. > > The operation is allowed only on a dying process. > > > > Previously I proposed a number of alternatives to accomplish this: > > - https://lore.kernel.org/patchwork/patch/1060407 extending > > Please use the msg-id based urls https://lore.kernel.org/lkml/20190411014353.113252-3-surenb@google.com/ Will do. Thanks! > > > pidfd_send_signal to allow memory reaping using oom_reaper thread; > > - https://lore.kernel.org/patchwork/patch/1338196 extending > > https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@google.com/ > > > pidfd_send_signal to reap memory of the target process synchronously from > > the context of the caller; > > - https://lore.kernel.org/patchwork/patch/1344419/ to add MADV_DONTNEED > > support for process_madvise implementing synchronous memory reaping. > > https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@google.com/ > > > The end of the last discussion culminated with suggestion to introduce a > > dedicated system call (https://lore.kernel.org/patchwork/patch/1344418/#1553875) > > https://lore.kernel.org/linux-api/20201223075712.GA4719@lst.de/ > > > The reasoning was that the new variant of process_madvise > > a) does not work on an address range > > b) is destructive > > c) doesn't share much code at all with the rest of process_madvise > > >From the userspace point of view it was awkward and inconvenient to provide > > memory range for this operation that operates on the entire address space. > > Using special flags or address values to specify the entire address space > > was too hacky. > > > > The API is as follows, > > > > int process_mrelease(int pidfd, unsigned int flags); > > > > DESCRIPTION > > The process_mrelease() system call is used to free the memory of > > a process which was sent a SIGKILL signal. > > This is not really precise. The implementation will allow to use the > syscall on any exiting or fatal signal received process. Not just those > that have been SIGKILLed, right? For the purpose of the man page I would > go with exiting process for the wording. Ack. > > > The pidfd selects the process referred to by the PID file > > descriptor. > > (See pidofd_open(2) for further information) > > > > The flags argument is reserved for future use; currently, this > > argument must be specified as 0. > > > > RETURN VALUE > > On success, process_mrelease() returns 0. On error, -1 is > > returned and errno is set to indicate the error. > > > > ERRORS > > EBADF pidfd is not a valid PID file descriptor. > > > > EAGAIN Failed to release part of the address space. > > > > EINTR The call was interrupted by a signal; see signal(7). > > > > EINVAL flags is not 0. > > > > EINVAL The task does not have a pending SIGKILL or its memory is > > shared with another process with no pending SIGKILL. > > again, wording here. I would go with > EINVAL The memory of the task cannot be released because the > process is not exiting, the address space is shared > with an alive process or there is a core dump is in > progress.. Ack. > > > > ENOSYS This system call is not supported by kernels built with no > > MMU support (CONFIG_MMU=n). > > > > ESRCH The target process does not exist (i.e., it has terminated > > and been waited on). > > > > Signed-off-by: Suren Baghdasaryan > > --- > > changes in v4: > > - Replaced mmap_read_lock() with mmap_read_lock_killable(), per Michal Hocko > > - Added EINTR error in the manual pages documentation > > > > mm/oom_kill.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 58 insertions(+) > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index c729a4c4a1ac..86727794b0a8 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -28,6 +28,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -1141,3 +1142,60 @@ void pagefault_out_of_memory(void) > > out_of_memory(&oc); > > mutex_unlock(&oom_lock); > > } > > + > > +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) > > +{ > > +#ifdef CONFIG_MMU > > + struct mm_struct *mm = NULL; > > + struct task_struct *task; > > + unsigned int f_flags; > > + struct pid *pid; > > + long ret = 0; > > + > > + if (flags != 0) > > + return -EINVAL; > > + > > + pid = pidfd_get_pid(pidfd, &f_flags); > > + if (IS_ERR(pid)) > > + return PTR_ERR(pid); > > + > > + task = get_pid_task(pid, PIDTYPE_PID); > > + if (!task) { > > + ret = -ESRCH; > > + goto put_pid; > > + } > > + > > + /* > > + * If the task is dying and in the process of releasing its memory > > + * then get its mm. > > + */ > > + task_lock(task); > > Don't we need find_lock_task_mm here? Yes, we do. Will fix in the next rev. > > > + if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) { > > + mm = task->mm; > > + mmget(mm); > > + } > > + task_unlock(task); > > + if (!mm) { > > Do we want to treat MMF_OOM_SKIP as a failure? Yeah, I don't think we want to create additional contention if oom-killer is already working on this mm. Should we return EBUSY in this case? Other possible options is ESRCH, indicating that this process is a goner, so don't bother. WDYT? > > > + ret = -EINVAL; > > + goto put_task; > > + } > > + > > + if (mmap_read_lock_killable(mm)) { > > + ret = -EINTR; > > + goto put_mm; > > + } > > + if (!__oom_reap_task_mm(mm)) > > + ret = -EAGAIN; > > + mmap_read_unlock(mm); > > + > > +put_mm: > > + mmput(mm); > > +put_task: > > + put_task_struct(task); > > +put_pid: > > + put_pid(pid); > > + return ret; > > +#else > > + return -ENOSYS; > > +#endif /* CONFIG_MMU */ > > +} > > -- > > 2.32.0.554.ge1b32706d8-goog > Thanks for the review! > -- > Michal Hocko > SUSE Labs