memcg: give current access to memory reserves if it's trying to die

When a memcg is oom and current has already received a SIGKILL, then give
it access to memory reserves with a higher scheduling priority so that it
may quickly exit and free its memory.

This is identical to the global oom killer and is done even before
checking for panic_on_oom: a pending SIGKILL here while panic_on_oom is
selected is guaranteed to have come from userspace; the thread only needs
access to memory reserves to exit and thus we don't unnecessarily panic
the machine until the kernel has no last resort to free memory.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 3100bc57036..62a5cec08a1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -549,6 +549,17 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
         unsigned int points = 0;
         struct task_struct *p;
 
+        /*
+         * If current has a pending SIGKILL, then automatically select it.  The
+         * goal is to allow it to allocate so that it may quickly exit and free
+         * its memory.
+         */
+        if (fatal_signal_pending(current)) {
+                set_thread_flag(TIF_MEMDIE);
+                boost_dying_task_prio(current, NULL);
+                return;
+        }
+
         check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0, NULL);
         limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT;
         read_lock(&tasklist_lock);