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From: Oleg Nesterov on 5 Apr 2010 10:30
This is the David's patch rediffed agains the recent changes in -mm.

As David pointed out, we should fix select_bad_process() which currently
always selects the first process which was not filtered out before
oom_badness(), no matter what oom_badness() returns.

Change the code to ignore the process if oom_badness() returns 0, this
matters Documentation/filesystems/proc.txt and this merely looks better.

This also allows us to do more cleanups:

- no need to check OOM_SCORE_ADJ_MIN in select_bad_process(),
oom_badness() returns 0 in this case.

- oom_badness() can simply return 0 instead of -1 if the task
has no ->mm.

Now we can make it "unsigned" again, the signness and the
special "points >= 0" in select_bad_process() was added to
preserve the current behaviour.

Suggested-by: David Rientjes <rientjes(a)google.com>
Signed-off-by: Oleg Nesterov <oleg(a)redhat.com>
---

include/linux/oom.h | 3 ++-
mm/oom_kill.c | 11 ++++-------
2 files changed, 6 insertions(+), 8 deletions(-)

--- MM/include/linux/oom.h~5_BADNESS_DONT_RET_NEGATIVE 2010-04-05 15:39:21.000000000 +0200
+++ MM/include/linux/oom.h 2010-04-05 15:44:49.000000000 +0200
@@ -40,7 +40,8 @@ enum oom_constraint {
CONSTRAINT_MEMORY_POLICY,
};

-extern int oom_badness(struct task_struct *p, unsigned long totalpages);
+extern unsigned int oom_badness(struct task_struct *p,
+ unsigned long totalpages);
extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
extern void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_flags);

--- MM/mm/oom_kill.c~5_BADNESS_DONT_RET_NEGATIVE 2010-04-05 15:39:21.000000000 +0200
+++ MM/mm/oom_kill.c 2010-04-05 16:09:58.000000000 +0200
@@ -153,7 +153,7 @@ static unsigned long oom_forkbomb_penalt
* predictable as possible. The goal is to return the highest value for the
* task consuming the most memory to avoid subsequent oom conditions.
*/
-int oom_badness(struct task_struct *p, unsigned long totalpages)
+unsigned int oom_badness(struct task_struct *p, unsigned long totalpages)
{
int points;

@@ -173,7 +173,7 @@ int oom_badness(struct task_struct *p, u

p = find_lock_task_mm(p);
if (!p)
- return -1;
+ return 0;
/*
* The baseline for the badness score is the proportion of RAM that each
* task's rss and swap space use.
@@ -294,7 +294,7 @@ static struct task_struct *select_bad_pr
*ppoints = 0;

for_each_process(p) {
- int points;
+ unsigned int points;

/* skip the init task and kthreads */
if (is_global_init(p) || (p->flags & PF_KTHREAD))
@@ -336,11 +336,8 @@ static struct task_struct *select_bad_pr
*ppoints = 1000;
}

- if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
- continue;
-
points = oom_badness(p, totalpages);
- if (points >= 0 && (points > *ppoints || !chosen)) {
+ if (points > *ppoints) {
chosen = p;
*ppoints = points;
}

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