From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
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@xxxxxxxxxx/
[2] https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@xxxxxxxxxx/
[3] https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@xxxxxxxxxx/
[4] https://lore.kernel.org/linux-api/20201223075712.GA4719@xxxxxx/
Link: https://lkml.kernel.org/r/20210809185259.405936-1-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Florian Weimer <fweimer@xxxxxxxxxx>
Cc: Jan Engelhardt <jengelh@xxxxxxx>
Cc: Tim Murray <timmurray@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
--- a/mm/oom_kill.c~mm-introduce-process_mrelease-system-call
+++ a/mm/oom_kill.c
@@ -28,6 +28,7 @@
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/swap.h>
+#include <linux/syscalls.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
#include <linux/cpuset.h>
@@ -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 */
+}
_
