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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A2730C4338F for ; Mon, 9 Aug 2021 11:55:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7293C6101E for ; Mon, 9 Aug 2021 11:55:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233156AbhHILzl (ORCPT ); Mon, 9 Aug 2021 07:55:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:46880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233069AbhHILzl (ORCPT ); Mon, 9 Aug 2021 07:55:41 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AB3C260F55; Mon, 9 Aug 2021 11:55:15 +0000 (UTC) Date: Mon, 9 Aug 2021 13:55:12 +0200 From: Christian Brauner To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, 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, 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 v8 1/2] mm: introduce process_mrelease system call Message-ID: <20210809115512.hdpj2cxqkmd3myee@wittgenstein> References: <20210808160823.3553954-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210808160823.3553954-1-surenb@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Sun, Aug 08, 2021 at 09:08:22AM -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 pidfd_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 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). > > [1] https://lore.kernel.org/lkml/20190411014353.113252-3-surenb@google.com/ > [2] https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@google.com/ > [3] https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@google.com/ > [4] https://lore.kernel.org/linux-api/20201223075712.GA4719@lst.de/ > > Link: https://lore.kernel.org/r/20210808160823.3553954-1-surenb@google.com > Signed-off-by: Suren Baghdasaryan > --- > changes in v8: > - Replaced mmget with mmgrab, per Shakeel Butt > - Refactored the code to simplify and fix the task_lock release issue, > per Michal Hocko > > mm/oom_kill.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 70 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index c729a4c4a1ac..f8acc26f7300 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1141,3 +1142,72 @@ 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; > + struct task_struct *p; > + unsigned int f_flags; > + bool reap = true; > + struct pid *pid; > + long ret = 0; > + > + if (flags) > + return -EINVAL; > + > + pid = pidfd_get_pid(pidfd, &f_flags); > + if (IS_ERR(pid)) > + return PTR_ERR(pid); > + > + task = get_pid_task(pid, PIDTYPE_PID); Technically, we really want PIDTYPE_TGID here. Currently, a pidfd can't be created for a thread that isn't a thread-group leader. And while we do make sure that when a pidfd is created the thread is a thread-group leader, i.e. has a PIDTYPE_TGID entry in its struct pid we might in the future not carry this restriction and will allow pidfds to refer to a single thread. When we do that we need to take a good look at all users carefully. So I'd prefer if this is changed to task = get_pid_task(pid, PIDTYPE_TGID); to clearly express that the assumption is that this is a thread-group leader. Otherwise, Acked-by: Christian Brauner