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SubjectRe: [PATCH] page-allocator: Ensure that processes that have been OOM killed exit the page allocator (resend)
On Thu, 16 Jul 2009, Mel Gorman wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4b8552e..b381a6b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1830,8 +1830,6 @@ rebalance:
> if (order > PAGE_ALLOC_COSTLY_ORDER &&
> !(gfp_mask & __GFP_NOFAIL))
> goto nopage;
> -
> - goto restart;
> }
> }
>
>

This isn't right (and not only because it'll add a compiler warning
because `restart' is now unused).

This would immediately fail any allocation that triggered the oom killer
and ended up being selected that isn't __GFP_NOFAIL, even if it would have
succeeded without even killing any task simply because it allocates
without watermarks.

It will also, coupled with your earlier patch, inappropriately warn about
an infinite loop with __GFP_NOFAIL even though it hasn't even attempted to
loop once since that decision is now handled by should_alloc_retry().

The liklihood of such an infinite loop, considering only one thread per
system (or cpuset) can be TIF_MEMDIE at a time, is very low. I've never
seen memory reserves completely depleted such that the next high-priority
allocation wouldn't succeed so that current could handle its pending
SIGKILL.

You get the same behavior with my patch, but are allowed to try the high
priority allocation again for the attempt that triggered the oom killer
(and not only subsequent ones).
---
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1789,6 +1789,10 @@ rebalance:
if (p->flags & PF_MEMALLOC)
goto nopage;

+ /* Avoid allocations with no watermarks from looping endlessly */
+ if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
+ goto nopage;
+
/* Try direct reclaim and then allocating */
page = __alloc_pages_direct_reclaim(gfp_mask, order,
zonelist, high_zoneidx,

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