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SubjectRe: [patch] oom: give current access to memory reserves if it has been killed
On Thu, 1 Apr 2010, Oleg Nesterov wrote:

> > Why? You ignored this part:
> >
> > Say, right after exit_mm() we are doing acct_process(), and f_op->write()
> > needs a page. So, you are saying that in this case __page_cache_alloc()
> > can never trigger out_of_memory() ?
> >
> > why this is not possible?
> >
> > David, I am not arguing, I am asking.
>
> In case I wasn't clear...
>
> Yes, currently __oom_kill_task(p) is not possible if p->mm == NULL.
>
> But your patch adds
>
> if (fatal_signal_pending(current))
> __oom_kill_task(current);
>
> into out_of_memory().
>

Ok, and it's possible during the tasklist scan if current is PF_EXITING
and that gets passed to oom_kill_process(), so we need the following
patch. Can I have your acked-by and then I'll propose it to Andrew with a
follow-up that merges __oom_kill_task() into oom_kill_task() since it only
has one caller now anyway?

[ Both of these situations will be current since the oom killer is a
no-op whenever another task is found to be PF_EXITING and
oom_kill_process() wouldn't get called with any other thread unless
oom_kill_quick is enabled or its VM_FAULT_OOM in which cases we kill
current as well. ]

Thanks Oleg.
---
mm/oom_kill.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -459,7 +459,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
* its children or threads, just set TIF_MEMDIE so it can die quickly
*/
if (p->flags & PF_EXITING) {
- __oom_kill_task(p);
+ set_tsk_thread_flag(p, TIF_MEMDIE);
return 0;
}

@@ -686,7 +686,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
* its memory.
*/
if (fatal_signal_pending(current)) {
- __oom_kill_task(current);
+ set_tsk_thread_flag(current, TIF_MEMDIE);
return;
}


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