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Mon, 09 Aug 2021 08:23:55 -0700 (PDT) MIME-Version: 1.0 References: <20210808160823.3553954-1-surenb@google.com> In-Reply-To: <20210808160823.3553954-1-surenb@google.com> From: Shakeel Butt Date: Mon, 9 Aug 2021 08:23:44 -0700 Message-ID: Subject: Re: [PATCH v8 1/2] mm: introduce process_mrelease system call To: Suren Baghdasaryan Cc: Andrew Morton , 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 , 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: 7EE6AD0004B0 Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=EsSKEKNS; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf15.hostedemail.com: domain of shakeelb@google.com designates 209.85.208.172 as permitted sender) smtp.mailfrom=shakeelb@google.com X-Stat-Signature: 5dphzfaw6sqof73984zgicu7mwwjtkhr X-HE-Tag: 1628522637-181023 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 Sun, Aug 8, 2021 at 9:08 AM 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/ > > Signed-off-by: Suren Baghdasaryan Reviewed-by: Shakeel Butt