From 884a7e5964e06ed93c7771c0d7cf19c09a8946f1 Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Thu, 2 Sep 2021 15:00:29 -0700 Subject: mm: introduce process_mrelease system call 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://lkml.kernel.org/r/20210809185259.405936-1-surenb@google.com Signed-off-by: Suren Baghdasaryan Reviewed-by: Shakeel Butt Acked-by: David Hildenbrand Acked-by: Michal Hocko Acked-by: Christian Brauner Cc: David Rientjes Cc: Matthew Wilcox (Oracle) Cc: Johannes Weiner Cc: Roman Gushchin Cc: Rik van Riel Cc: Minchan Kim Cc: Christoph Hellwig Cc: Oleg Nesterov Cc: Jann Horn Cc: Geert Uytterhoeven Cc: Andy Lutomirski Cc: Christian Brauner Cc: Florian Weimer Cc: Jan Engelhardt Cc: Tim Murray Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) (limited to 'mm/oom_kill.c') diff --git a/mm/oom_kill.c b/mm/oom_kill.c index c729a4c4a1ac..831340e7ad8b 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_TGID); + if (!task) { + ret = -ESRCH; + goto put_pid; + } + + /* + * Make sure to choose a thread which still has a reference to mm + * during the group exit + */ + p = find_lock_task_mm(task); + if (!p) { + ret = -ESRCH; + goto put_task; + } + + mm = p->mm; + mmgrab(mm); + + /* If the work has been done already, just exit with success */ + if (test_bit(MMF_OOM_SKIP, &mm->flags)) + reap = false; + else if (!task_will_free_mem(p)) { + reap = false; + ret = -EINVAL; + } + task_unlock(p); + + if (!reap) + goto drop_mm; + + if (mmap_read_lock_killable(mm)) { + ret = -EINTR; + goto drop_mm; + } + if (!__oom_reap_task_mm(mm)) + ret = -EAGAIN; + mmap_read_unlock(mm); + +drop_mm: + mmdrop(mm); +put_task: + put_task_struct(task); +put_pid: + put_pid(pid); + return ret; +#else + return -ENOSYS; +#endif /* CONFIG_MMU */ +} -- cgit v1.2.3