From 35451beecbd7c86ce3249d543594517a5fe9a0cd Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Date: Mon, 21 Sep 2009 17:02:27 -0700
Subject: [PATCH] ksm: unmerge is an origin of OOMs

Just as the swapoff system call allocates many pages of RAM to various
processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
(unmerge) is liable to allocate many pages of RAM to various processes,
perhaps triggering OOM; and each is normally run from a modest admin
process (swapoff or shell), easily repeated until it succeeds.

So treat unmerge_and_remove_all_rmap_items() in the same way that we treat
try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and bracket both
with that, to ask the OOM killer to kill them first, to prevent them from
spawning more and more OOM kills.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/sched.h | 2 +-
 mm/ksm.c              | 2 ++
 mm/oom_kill.c         | 2 +-
 mm/swapfile.c         | 4 ++--
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8f3e63cb33a6..899d7304d594 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1720,7 +1720,7 @@ extern cputime_t task_gtime(struct task_struct *p);
 #define PF_FROZEN	0x00010000	/* frozen for system suspend */
 #define PF_FSTRANS	0x00020000	/* inside a filesystem transaction */
 #define PF_KSWAPD	0x00040000	/* I am kswapd */
-#define PF_SWAPOFF	0x00080000	/* I am in swapoff */
+#define PF_OOM_ORIGIN	0x00080000	/* Allocating much memory to others */
 #define PF_LESS_THROTTLE 0x00100000	/* Throttle me less: I clean memory */
 #define PF_KTHREAD	0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE	0x00400000	/* randomize virtual address space */
diff --git a/mm/ksm.c b/mm/ksm.c
index e11e7a5ac84f..37cc37325094 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1557,7 +1557,9 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (ksm_run != flags) {
 		ksm_run = flags;
 		if (flags & KSM_RUN_UNMERGE) {
+			current->flags |= PF_OOM_ORIGIN;
 			err = unmerge_and_remove_all_rmap_items();
+			current->flags &= ~PF_OOM_ORIGIN;
 			if (err) {
 				ksm_run = KSM_RUN_STOP;
 				count = err;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a7b2460e922b..da4c342f2641 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -79,7 +79,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	/*
 	 * swapoff can easily use up all memory, so kill those first.
 	 */
-	if (p->flags & PF_SWAPOFF)
+	if (p->flags & PF_OOM_ORIGIN)
 		return ULONG_MAX;
 
 	/*
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 74f1102e8749..f1bf19daadc6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1575,9 +1575,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	p->flags &= ~SWP_WRITEOK;
 	spin_unlock(&swap_lock);
 
-	current->flags |= PF_SWAPOFF;
+	current->flags |= PF_OOM_ORIGIN;
 	err = try_to_unuse(type);
-	current->flags &= ~PF_SWAPOFF;
+	current->flags &= ~PF_OOM_ORIGIN;
 
 	if (err) {
 		/* re-insert swap space back into swap_list */