oom: add per-mm oom disable count
It's pointless to kill a task if another thread sharing its mm cannot be
killed to allow future memory freeing. A subsequent patch will prevent
kills in such cases, but first it's necessary to have a way to flag a task
that shares memory with an OOM_DISABLE task that doesn't incur an
additional tasklist scan, which would make select_bad_process() an O(n^2)
function.
This patch adds an atomic counter to struct mm_struct that follows how
many threads attached to it have an oom_score_adj of OOM_SCORE_ADJ_MIN.
They cannot be killed by the kernel, so their memory cannot be freed in
oom conditions.
This only requires task_lock() on the task that we're operating on, it
does not require mm->mmap_sem since task_lock() pins the mm and the
operation is atomic.
[rientjes@google.com: changelog and sys_unshare() code]
[rientjes@google.com: protect oom_disable_count with task_lock in fork]
[rientjes@google.com: use old_mm for oom_disable_count in exec]
Signed-off-by: Ying Han <yinghan@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/fork.c b/kernel/fork.c
index c445f8c..e87aaaa 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -65,6 +65,7 @@
#include <linux/perf_event.h>
#include <linux/posix-timers.h>
#include <linux/user-return-notifier.h>
+#include <linux/oom.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -488,6 +489,7 @@
mm->cached_hole_size = ~0UL;
mm_init_aio(mm);
mm_init_owner(mm, p);
+ atomic_set(&mm->oom_disable_count, 0);
if (likely(!mm_alloc_pgd(mm))) {
mm->def_flags = 0;
@@ -741,6 +743,8 @@
/* Initializing for Swap token stuff */
mm->token_priority = 0;
mm->last_interval = 0;
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_inc(&mm->oom_disable_count);
tsk->mm = mm;
tsk->active_mm = mm;
@@ -1299,8 +1303,13 @@
bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
bad_fork_cleanup_mm:
- if (p->mm)
+ if (p->mm) {
+ task_lock(p);
+ if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&p->mm->oom_disable_count);
+ task_unlock(p);
mmput(p->mm);
+ }
bad_fork_cleanup_signal:
if (!(clone_flags & CLONE_THREAD))
free_signal_struct(p->signal);
@@ -1693,6 +1702,10 @@
active_mm = current->active_mm;
current->mm = new_mm;
current->active_mm = new_mm;
+ if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+ atomic_dec(&mm->oom_disable_count);
+ atomic_inc(&new_mm->oom_disable_count);
+ }
activate_mm(active_mm, new_mm);
new_mm = mm;
}