Messages in this thread Patch in this message | | | Date | Mon, 26 Jun 2006 18:20:38 +0200 | From | Nick Piggin <> | Subject | [rfc][patch] fixes for several oom killer problems |
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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.
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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 <npiggin@suse.de>
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) { - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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