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oom: add per-mm oom disable count

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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>
This commit is contained in:
Ying Han
2010-10-26 14:21:23 -07:00
committed by Linus Torvalds
parent 0f4d208f19
commit 3d5992d2ac
5 changed files with 54 additions and 1 deletions
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30
fs/proc/base.c
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@@ -1047,6 +1047,21 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
return -EACCES;
}
task_lock(task);
if (!task->mm) {
task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
return -EINVAL;
}
if (oom_adjust != task->signal->oom_adj) {
if (oom_adjust == OOM_DISABLE)
atomic_inc(&task->mm->oom_disable_count);
if (task->signal->oom_adj == OOM_DISABLE)
atomic_dec(&task->mm->oom_disable_count);
}
/*
* Warn that /proc/pid/oom_adj is deprecated, see
* Documentation/feature-removal-schedule.txt.
@@ -1065,6 +1080,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
else
task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /
-OOM_DISABLE;
task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
@@ -1133,6 +1149,19 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
return -EACCES;
}
task_lock(task);
if (!task->mm) {
task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
return -EINVAL;
}
if (oom_score_adj != task->signal->oom_score_adj) {
if (oom_score_adj == OOM_SCORE_ADJ_MIN)
atomic_inc(&task->mm->oom_disable_count);
if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
atomic_dec(&task->mm->oom_disable_count);
}
task->signal->oom_score_adj = oom_score_adj;
/*
* Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
@@ -1143,6 +1172,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
else
task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /
OOM_SCORE_ADJ_MAX;
task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
return count;