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Wed, 04 Aug 2021 15:55:11 -0700 (PDT) MIME-Version: 1.0 References: <20210804185004.1304692-1-surenb@google.com> <20210804155024.e4e42e1b7b087937271fa7ce@linux-foundation.org> In-Reply-To: <20210804155024.e4e42e1b7b087937271fa7ce@linux-foundation.org> From: Suren Baghdasaryan Date: Wed, 4 Aug 2021 15:55:00 -0700 Message-ID: Subject: Re: [PATCH v6 1/2] mm: introduce process_mrelease system call To: Andrew Morton Cc: Michal Hocko , Michal Hocko , 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" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 7FE69300ACF9 Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b="je/d+I73"; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf03.hostedemail.com: domain of surenb@google.com designates 209.85.219.171 as permitted sender) smtp.mailfrom=surenb@google.com X-Stat-Signature: igagrpt5pq8za6zaiqdtxof18sbwsixd X-HE-Tag: 1628117712-25378 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 4, 2021 at 3:50 PM Andrew Morton wrote: > > 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/ Thanks! > > > > > 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? Let me take a stab at it. Thanks!