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ksm: unmerge is an origin of OOMs

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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>
This commit is contained in:
Hugh Dickins
2009-09-21 17:02:27 -07:00
committed by Linus Torvalds
parent a913e182ab
commit 35451beecb
4 changed files with 6 additions and 4 deletions
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2
mm/ksm.c
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@@ -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;