Hi,
We have reports of OOM killer panicing the system even if there are
tasks currently exiting and/or plenty able to be freed.
The main problem is the cpuset_excl_nodes_overlap causing an immediate
panic if current is exiting; I haven't got confirmation of whether
or not a minimal patch for that is effective.
The minimal patch basically involved ripping out the test completely.
I'd rather something more comprehensive in mainline, and I spotted
several other issues as well.
---
Fix several OOM killer problems.
Big ones:
- cpuset_excl_nodes_overlap always returns 0 if current is exiting. This
caused customer's systems to panic in the OOM killer when processes were
having trouble getting memory for the final put_user in mm_release. Even
though there were lots of processes to kill. Fix this by just causing
cpuset_excl_nodes_overlap to reduce the badness rather than disallow it
(it may still be pinning memory somehow on this node or that this task
may use).
- If current *is* exiting, it should actually be allowed to access reserved
memory rather than OOM kill something else. Can't do this via a straight
check in page_alloc.c because that would allow multiple tasks to use up
reserves. Instead cause current to wind up marking itself as TIF_MEMDIE.
- In cpuset_excl_nodes_overlap, return 1 for PF_EXITING tasks. This retains
parity with !CONFIG_CPUSETS case.
Little ones:
- PF_SWAPOFF processes cause select_bad_process to return straight away.
Instead, give them high priority and ensure no parallel OOM kills are
happening at the same time.
- cpuset_exlc_nodes_overlap may still free up some memory we're allowed to
use. Kernel allocated memory, memory touched first by other processes or
when we were in a different group. Cause this just to minimise the
badness of a process.
- Skip kernel threads, rather than having them return 0 from badness.
Theoretically, badness might truncate all results to 0, thus a kernel
thread might be picked first, causing an infinite loop.
- Skip PF_DEAD tasks, for similar reasons.
- Print the name of the task that invoked the OOM killer. Could make
debugging easier.
Signed-off-by: Nick Piggin <[email protected]>
Index: linux-2.6/mm/oom_kill.c
===================================================================
--- linux-2.6.orig/mm/oom_kill.c
+++ linux-2.6/mm/oom_kill.c
@@ -57,6 +57,12 @@ unsigned long badness(struct task_struct
}
/*
+ * swapoff can easily use up all memory, so kill those first.
+ */
+ if (p->flags & PF_SWAPOFF)
+ return ULONG_MAX;
+
+ /*
* The memory size of the process is the basis for the badness.
*/
points = mm->total_vm;
@@ -125,6 +131,15 @@ unsigned long badness(struct task_struct
if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
points /= 4;
+
+ /*
+ * If p's nodes don't overlap ours, it may still help to kill p
+ * because p may have allocated or otherwise mapped memory on
+ * this node before. However it will be less likely.
+ */
+ if (!cpuset_excl_nodes_overlap(p))
+ points /= 4;
+
/*
* Adjust the score by oomkilladj.
*/
@@ -190,25 +205,35 @@ static struct task_struct *select_bad_pr
unsigned long points;
int releasing;
+ /* skip kernel threads */
+ if (!p->mm)
+ continue;
/* skip the init task with pid == 1 */
if (p->pid == 1)
continue;
- if (p->oomkilladj == OOM_DISABLE)
- continue;
- /* If p's nodes don't overlap ours, it won't help to kill p. */
- if (!cpuset_excl_nodes_overlap(p))
- continue;
/*
* This is in the process of releasing memory so for wait it
* to finish before killing some other task by mistake.
+ *
+ * However, if p is the current task, we allow the 'kill' to
+ * go ahead if it is exiting: this will simply set TIF_MEMDIE,
+ * which will allow it to gain access to memory reserves in
+ * the process of exiting and releasing its resources.
*/
releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
p->flags & PF_EXITING;
- if (releasing && !(p->flags & PF_DEAD))
+ if (releasing) {
+ /* PF_DEAD tasks have already released their mm */
+ if (p->flags & PF_DEAD)
+ continue;
+ if (p == current) {
+ chosen = p;
+ *ppoints = ULONG_MAX;
+ continue;
+ }
return ERR_PTR(-1UL);
- if (p->flags & PF_SWAPOFF)
- return p;
+ }
points = badness(p, uptime.tv_sec);
if (points > *ppoints || !chosen) {
@@ -216,6 +241,7 @@ static struct task_struct *select_bad_pr
*ppoints = points;
}
} while_each_thread(g, p);
+
return chosen;
}
@@ -319,8 +345,8 @@ void out_of_memory(struct zonelist *zone
unsigned long points = 0;
if (printk_ratelimit()) {
- printk("oom-killer: gfp_mask=0x%x, order=%d\n",
- gfp_mask, order);
+ printk(KERN_WARNING "%s invoked oom-killer: "
+ "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", current->comm, gfp_mask, order, current->oomkilladj);
dump_stack();
show_mem();
}
Index: linux-2.6/kernel/cpuset.c
===================================================================
--- linux-2.6.orig/kernel/cpuset.c
+++ linux-2.6/kernel/cpuset.c
@@ -2362,7 +2362,7 @@ EXPORT_SYMBOL_GPL(cpuset_mem_spread_node
int cpuset_excl_nodes_overlap(const struct task_struct *p)
{
const struct cpuset *cs1, *cs2; /* my and p's cpuset ancestors */
- int overlap = 0; /* do cpusets overlap? */
+ int overlap = 1; /* do cpusets overlap? */
task_lock(current);
if (current->flags & PF_EXITING) {
-
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