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Commit 35451bee authored Sep 21, 2009 by Hugh Dickins Committed by Linus Torvalds Sep 22, 2009

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>

parent a913e182

include/linux/sched.h

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1720,7 +1720,7 @@ extern cputime_t task_gtime(struct task_struct *p);
	#define PF_FROZEN 0x00010000 /* frozen for system suspend */		#define PF_FROZEN 0x00010000 /* frozen for system suspend */
	#define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */		#define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */
	#define PF_KSWAPD 0x00040000 /* I am kswapd */		#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_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */
	#define PF_KTHREAD 0x00200000 /* I am a kernel thread */		#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
	#define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */		#define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */

mm/ksm.c

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -1557,7 +1557,9 @@ static ssize_t run_store(struct kobject kobj, struct kobj_attribute attr,
	if (ksm_run != flags) {		if (ksm_run != flags) {
	ksm_run = flags;		ksm_run = flags;
	if (flags & KSM_RUN_UNMERGE) {		if (flags & KSM_RUN_UNMERGE) {
			current->flags \|= PF_OOM_ORIGIN;
	err = unmerge_and_remove_all_rmap_items();		err = unmerge_and_remove_all_rmap_items();
			current->flags &= ~PF_OOM_ORIGIN;
	if (err) {		if (err) {
	ksm_run = KSM_RUN_STOP;		ksm_run = KSM_RUN_STOP;
	count = err;		count = err;

mm/oom_kill.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -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.		* 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;		return ULONG_MAX;

	/*		/*

mm/swapfile.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -1575,9 +1575,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
	p->flags &= ~SWP_WRITEOK;		p->flags &= ~SWP_WRITEOK;
	spin_unlock(&swap_lock);		spin_unlock(&swap_lock);

	current->flags \|= PF_SWAPOFF;		current->flags \|= PF_OOM_ORIGIN;
	err = try_to_unuse(type);		err = try_to_unuse(type);
	current->flags &= ~PF_SWAPOFF;		current->flags &= ~PF_OOM_ORIGIN;

	if (err) {		if (err) {
	/* re-insert swap space back into swap_list */		/* re-insert swap space back into swap_list */