[...]
Previously I proposed a number of alternatives to accomplish this:
- https://lore.kernel.org/patchwork/patch/1060407 extending
I have no idea how stable these links are. Referencing via message id is
the common practice. For this link, we'd use
https://lkml.kernel.org/r/20190411014353.113252-3-surenb@xxxxxxxxxx/
instead.
pidfd_send_signal to allow memory reaping using oom_reaper thread;
- https://lore.kernel.org/patchwork/patch/1338196 extending
pidfd_send_signal to reap memory of the target process synchronously from
the context of the caller;
- https://lore.kernel.org/patchwork/patch/1344419/ to add MADV_DONTNEED
support for process_madvise implementing synchronous memory reaping.
The end of the last discussion culminated with suggestion to introduce a
dedicated system call (https://lore.kernel.org/patchwork/patch/1344418/#1553875)
The reasoning was that the new variant of process_madvise
a) does not work on an address range
b) is destructive
c) doesn't share much code at all with the rest of process_madvise
From the userspace point of view it was awkward and inconvenient to provide
memory range for this operation that operates on the entire address space.
Using special flags or address values to specify the entire address space
was too hacky.
I'd condense this description and only reference previous discussions to
put a main focus on what this patch actually does. Like
"
After previous discussions [1, 2, 3] the decision was made to introduce
a dedicated system call to cover this use case.
...
[1] https://lkml.kernel.org/r/20190411014353.113252-3-surenb@xxxxxxxxxx/
"
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
a process which was sent a SIGKILL signal.
The pidfd selects the process referred to by the PID file
descriptor.
(See pidofd_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 task does not have a pending SIGKILL or its memory is
shared with another process with no pending SIGKILL.
Hm, I do wonder if it would make sense to have a mode (e.g., via a flag)
to reap all but shared memory from a dying process. Future work.
ENOSYS This system call is not supported by kernels built with no
MMU support (CONFIG_MMU=n).
Maybe "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).
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
changes in v4:
- Replaced mmap_read_lock() with mmap_read_lock_killable(), per Michal Hocko
- Added EINTR error in the manual pages documentation
mm/oom_kill.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 58 insertions(+)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c729a4c4a1ac..86727794b0a8 100644
--- a/mm/oom_kill.c
+++ b/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 +1142,60 @@ 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;
+ unsigned int f_flags;
+ struct pid *pid;
+ long ret = 0;
+
+ if (flags != 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);
+ if (!task) {
+ ret = -ESRCH;
+ goto put_pid;
+ }
+
+ /*
+ * If the task is dying and in the process of releasing its memory
+ * then get its mm.
+ */
+ task_lock(task);
+ if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) {
+ mm = task->mm;
+ mmget(mm);
+ }
+ task_unlock(task);
+ if (!mm) {
+ ret = -EINVAL;
+ goto put_task;
+ }
+
+ if (mmap_read_lock_killable(mm)) {
+ ret = -EINTR;
+ goto put_mm;
+ }
+ if (!__oom_reap_task_mm(mm))
+ ret = -EAGAIN;
I'm not an expert on __oom_reap_task_mm(), but the whole approach makes
sense to. So feel free to add my
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
