On Thu 05-09-13 07:54:30, Johannes Weiner wrote:
[...]
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Subject: [patch] mm: memcg: handle non-error OOM situations more gracefully
>
> Many places that can trigger a memcg OOM situation return gracefully
> and don't propagate VM_FAULT_OOM up the fault stack.
>
> It's not practical to annotate all of them to disable the memcg OOM
> killer. Instead, just clean up any set OOM state without warning in
> case the fault is not returning VM_FAULT_OOM.
>
> Also fail charges immediately when the current task already is in an
> OOM context. Otherwise, the previous context gets overwritten and the
> memcg reference is leaked.
Could you paste find_or_create_page called from __get_blk as an example
here, please? So that we do not have to scratch our heads again later...
Also task_in_memcg_oom could be stuffed into mem_cgroup_disable_oom
branch to reduce an overhead for in-kernel faults. The overhead
shouldn't be noticeable so I am not sure this is that important.
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
I do not see any easier way to fix this without returning back to the
old behavior which is much worse.
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Thanks!
> diff --git a/mm/memory.c b/mm/memory.c
> index cdbe41b..cdad471 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -57,7 +57,6 @@
> #include <linux/swapops.h>
> #include <linux/elf.h>
> #include <linux/gfp.h>
> -#include <linux/stacktrace.h>
>
> #include <asm/io.h>
> #include <asm/pgalloc.h>
> @@ -3521,11 +3520,8 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> if (flags & FAULT_FLAG_USER)
> mem_cgroup_disable_oom();
>
> - if (WARN_ON(task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))) {
> - printk("Fixing unhandled memcg OOM context set up from:\n");
> - print_stack_trace(¤t->memcg_oom.trace, 0);
> - mem_cgroup_oom_synchronize();
> - }
> + if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
> + mem_cgroup_oom_synchronize(false);
>
> return ret;
> }
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index aa60863..3bf664c 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -785,7 +785,7 @@ out:
> */
> void pagefault_out_of_memory(void)
> {
> - if (mem_cgroup_oom_synchronize())
> + if (mem_cgroup_oom_synchronize(true))
> return;
> if (try_set_system_oom()) {
> out_of_memory(NULL, 0, 0, NULL);
> --
> 1.8.4
>
--
Michal Hocko
SUSE Labs
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