Commit 35451bee authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: default avatarIzik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a913e182

include/linux/sched.h

+1 −1
Original line number 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_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 */

mm/ksm.c

+2 −0
Original line number 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) {

		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;

mm/oom_kill.c

+1 −1
Original line number 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.

	 */

	if (p->flags & PF_SWAPOFF)

	if (p->flags & PF_OOM_ORIGIN)

		return ULONG_MAX;



	/*

mm/swapfile.c

+2 −2
Original line number Diff line number Diff line
@@ -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 */

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