Re: Mem issues in 2.6.9 (ever since 2.6.9-rc3) and possible cause

Thomas Gleixner
2004-10-31T12:42:31Z

[-- Attachment #1: Type: text/plain, Size: 951 bytes --]

> But it still does not fix the random madness of oom-killer. Once it is
> triggered it keeps going even if there is 50MB free memory available.
>

Additionally to Rik's and Kame's fixes, I changed the criterias in
oom_kill a bit to

- take processes which fork a lot of children into account instead of
killing stuff like portmap and sshd just because they haven't used a lot
of CPU time since they started.

- prevent oom-killer to continue to kill processes, even if memory is
available

I was facing the above problems on a small embedded system, where a
forking server started to flood the machine with child processes.
oom-killer killed portmap and sshd instead of the real culprit and took
away the opportunity to log into the machine remotely.

The problem can be simulated with hackbench on a small UP system.

I don't know, if these changes have any negative impacts on the
testcases which were used in the original design. Rik ??

tglx

[-- Attachment #2: oom_kill.c.diff --]
[-- Type: text/x-patch, Size: 4147 bytes --]

--- 2.6.10-rc1-mm2.orig/mm/oom_kill.c 2004-10-31 11:13:32.000000000 +0100
+++ 2.6.10-rc1-mm2/mm/oom_kill.c 2004-10-31 13:00:06.000000000 +0100
@@ -45,8 +45,10 @@
static unsigned long badness(struct task_struct *p, unsigned long uptime)
{
unsigned long points, cpu_time, run_time, s;
+ struct list_head *tsk;

- if (!p->mm)
+ /* Ignore mm-less tasks and init */
+ if (!p->mm || p->pid == 1)
return 0;

if (p->flags & PF_MEMDIE)
@@ -57,6 +59,19 @@
points = p->mm->total_vm;

/*
+ * Processes which fork a lot of child processes are likely
+ * a good choice. We add the vmsize of the childs if they
+ * have an own mm. This prevents forking servers to flood the
+ * machine with an endless amount of childs
+ */
+ list_for_each(tsk, &p->children) {
+ struct task_struct *chld;
+ chld = list_entry(tsk, struct task_struct, sibling);
+ if (chld->mm != p->mm && chld->mm)
+ points += chld->mm->total_vm;
+ }
+
+ /*
* CPU time is in tens of seconds and run time is in thousands
* of seconds. There is no particular reason for this other than
* that it turned out to work very well in practice.
@@ -176,6 +191,27 @@
return mm;
}

+static struct mm_struct *oom_kill_process(task_t *p)
+{
+ struct mm_struct *mm;
+ struct task_struct *g, *q;
+
+ mm = oom_kill_task(p);
+ if (!mm)
+ return NULL;
+ /*
+ * kill all processes that share the ->mm (i.e. all threads),
+ * but are in a different thread group
+ */
+ do_each_thread(g, q)
+ if (q->mm == mm && q->tgid != p->tgid)
+ __oom_kill_task(q);
+
+ while_each_thread(g, q);
+ if (!p->mm)
+ printk(KERN_INFO "Fixed up OOM kill of mm-less task\n");
+ return mm;
+}

/**
* oom_kill - kill the "best" process when we run out of memory
@@ -188,7 +224,9 @@
void oom_kill(void)
{
struct mm_struct *mm;
- struct task_struct *g, *p, *q;
+ struct task_struct *c, *p;
+ struct list_head *tsk;
+ int mmcnt = 0;

read_lock(&tasklist_lock);
retry:
@@ -200,21 +238,25 @@
panic("Out of memory and no killable processes...\n");
}

- mm = oom_kill_task(p);
- if (!mm)
- goto retry;
/*
- * kill all processes that share the ->mm (i.e. all threads),
- * but are in a different thread group
+ * Kill the child processes first
*/
- do_each_thread(g, q)
- if (q->mm == mm && q->tgid != p->tgid)
- __oom_kill_task(q);
- while_each_thread(g, q);
- if (!p->mm)
- printk(KERN_INFO "Fixed up OOM kill of mm-less task\n");
+ list_for_each(tsk, &p->children) {
+ c = list_entry(tsk, struct task_struct, sibling);
+ if (c->mm == p->mm)
+ continue;
+ mm = oom_kill_process(c);
+ if (mm) {
+ mmcnt ++;
+ mmput(mm);
+ }
+ }
+ mm = oom_kill_process(p);
+ if (!mmcnt && !mm)
+ goto retry;
+ if (mm)
+ mmput(mm);
read_unlock(&tasklist_lock);
- mmput(mm);
return;
}

@@ -224,14 +266,22 @@
void out_of_memory(int gfp_mask)
{
/*
- * oom_lock protects out_of_memory()'s static variables.
- * It's a global lock; this is not performance-critical.
+ * inprogress protects out_of_memory()'s static variables.
+ * We don't use a spin_lock here, as spinlocks are
+ * nops on UP systems.
*/
- static spinlock_t oom_lock = SPIN_LOCK_UNLOCKED;
+ static unsigned long inprogress;
static unsigned long first, last, count, lastkill;
+ static unsigned int freepages = 1000000;
unsigned long now, since;

- spin_lock(&oom_lock);
+ if (test_and_set_bit(0, &inprogress))
+ return;
+
+ /* Check, if memory was freed since the last oom kill */
+ if (freepages < nr_free_pages())
+ goto out_unlock;
+
now = jiffies;
since = now - last;
last = now;
@@ -274,9 +324,8 @@

printk("oom-killer: gfp_mask=0x%x\n", gfp_mask);
show_free_areas();
-
- /* oom_kill() sleeps */
- spin_unlock(&oom_lock);
+ /* Store free pages * 2 for the check above */
+ freepages = (nr_free_pages() << 1);
oom_kill();
/*
* Make kswapd go out of the way, so "p" has a good chance of
@@ -284,7 +333,6 @@
* for more memory.
*/
yield();
- spin_lock(&oom_lock);

reset:
/*
@@ -294,7 +342,7 @@
if (time_after(now, first))
first = now;
count = 0;
-
+
out_unlock:
- spin_unlock(&oom_lock);
+ clear_bit(0, &inprogress);
}