Commit fb794bcb authored Aug 06, 2014 by David Rientjes Committed by Linus Torvalds Aug 06, 2014

mm, oom: remove unnecessary exit_state check



The oom killer scans each process and determines whether it is eligible
for oom kill or whether the oom killer should abort because of
concurrent memory freeing.  It will abort when an eligible process is
found to have TIF_MEMDIE set, meaning it has already been oom killed and
we're waiting for it to exit.

Processes with task->mm == NULL should not be considered because they
are either kthreads or have already detached their memory and killing
them would not lead to memory freeing.  That memory is only freed after
exit_mm() has returned, however, and not when task->mm is first set to
NULL.

Clear TIF_MEMDIE after exit_mm()'s mmput() so that an oom killed process
is no longer considered for oom kill, but only until exit_mm() has
returned.  This was fragile in the past because it relied on
exit_notify() to be reached before no longer considering TIF_MEMDIE
processes.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d0177639

kernel/exit.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -455,6 +455,7 @@ static void exit_mm(struct task_struct * tsk)
		task_unlock(tsk);
		mm_update_next_owner(mm);
		mmput(mm);
		clear_thread_flag(TIF_MEMDIE);
		}

		/*

mm/oom_kill.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -258,8 +258,6 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
		unsigned long totalpages, const nodemask_t *nodemask,
		bool force_kill)
		{
		if (task->exit_state)
		return OOM_SCAN_CONTINUE;
		if (oom_unkillable_task(task, NULL, nodemask))
		return OOM_SCAN_CONTINUE;