[PATCH 2/3] ksm: unmerge is an origin of OOMs

From: Hugh Dickins
Date: Sat Sep 05 2009 - 17:26:18 EST


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@xxxxxxxxxxxxx>
---

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(-)

--- mmotm/include/linux/sched.h 2009-09-05 14:40:16.000000000 +0100
+++ linux/include/linux/sched.h 2009-09-05 16:41:55.000000000 +0100
@@ -1755,7 +1755,7 @@ extern cputime_t task_gtime(struct task_
#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 */
--- mmotm/mm/ksm.c 2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/ksm.c 2009-09-05 16:41:55.000000000 +0100
@@ -1564,7 +1564,9 @@ static ssize_t run_store(struct kobject
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;
--- mmotm/mm/oom_kill.c 2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/oom_kill.c 2009-09-05 16:41:55.000000000 +0100
@@ -103,7 +103,7 @@ unsigned long badness(struct task_struct
/*
* 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;

/*
--- mmotm/mm/swapfile.c 2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/swapfile.c 2009-09-05 16:41:55.000000000 +0100
@@ -1573,9 +1573,9 @@ SYSCALL_DEFINE1(swapoff, const char __us
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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