x86,mm: make pagefault killable

When an oom killing occurs, almost all processes are getting stuck at the
following two points.

	1) __alloc_pages_nodemask
	2) __lock_page_or_retry

1) is not very problematic because TIF_MEMDIE leads to an allocation
failure and getting out from page allocator.

2) is more problematic.  In an OOM situation, zones typically don't have
page cache at all and memory starvation might lead to greatly reduced IO
performance.  When a fork bomb occurs, TIF_MEMDIE tasks don't die quickly,
meaning that a fork bomb may create new process quickly rather than the
oom-killer killing it.  Then, the system may become livelocked.

This patch makes the pagefault interruptible by SIGKILL.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1746f67c33de..57d3d5fade16 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -153,6 +153,7 @@ extern pgprot_t protection_map[16];
 #define FAULT_FLAG_MKWRITE      0x04    /* Fault was mkwrite of existing pte */
 #define FAULT_FLAG_ALLOW_RETRY  0x08    /* Retry fault if blocking */
 #define FAULT_FLAG_RETRY_NOWAIT 0x10    /* Don't drop mmap_sem and wait when retrying */
+#define FAULT_FLAG_KILLABLE     0x20    /* The fault task is in SIGKILL killable region */
 
 /*
  * This interface is used by x86 PAT code to identify a pfn mapping that is