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=-10.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 2C96AC4320A for ; Wed, 4 Aug 2021 22:50:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12DDF61073 for ; Wed, 4 Aug 2021 22:50:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235277AbhHDWum (ORCPT ); Wed, 4 Aug 2021 18:50:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:34802 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229775AbhHDWum (ORCPT ); Wed, 4 Aug 2021 18:50:42 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8D76F601FE; Wed, 4 Aug 2021 22:50:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1628117428; bh=au1jMsHrlZQGAFtzrot7CCPS+RgEAXFEcGYA0uxvwUA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=O4pj+MUbZwCirnYWew8Dlfb93x0HyiTgZGzxQRxfDe2cCKD9mmUaO/UBk3HS5o85X +iXxVrhGnbwzdi1E8oJHSppWyTUsv/w/Crsj4UEOIdnq3i7j+tsAGvPAtI8QFWeoMG MavZmyqLfP1+ptt0e4qk0PPEXD3nST0irkff/xDA= Date: Wed, 4 Aug 2021 15:50:24 -0700 From: Andrew Morton To: Suren Baghdasaryan Cc: mhocko@kernel.org, mhocko@suse.com, rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org, guro@fb.com, riel@surriel.com, minchan@kernel.org, christian@brauner.io, hch@infradead.org, oleg@redhat.com, david@redhat.com, jannh@google.com, shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de, timmurray@google.com, linux-api@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v6 1/2] mm: introduce process_mrelease system call Message-Id: <20210804155024.e4e42e1b7b087937271fa7ce@linux-foundation.org> In-Reply-To: <20210804185004.1304692-1-surenb@google.com> References: <20210804185004.1304692-1-surenb@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, 4 Aug 2021 11:50:03 -0700 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. > > After previous discussions [1, 2, 3] the decision was made [4] to introduce > a dedicated system call to cover this use case. > > 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 > an exiting process. > > The pidfd selects the process referred to by the PID file > descriptor. > (See pidofd_open(2) for further information) I did s/pidofd_open/pidfd_open/ > > 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 memory of the task cannot be released because the > process is not exiting, the address space is shared > with another live process or there is a core dump in > progress. > > ENOSYS This system call is not supported, for example, without > MMU support built into Linux. > > ESRCH The target process does not exist (i.e., it has terminated > and been waited on). > > ... > > mm/oom_kill.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 65 insertions(+) The code is nice and simple. Can we get a test suite into tools/testing/selftests?