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SubjectRe: [PATCH] page-allocator: Ensure that processes that have been OOM killed exit the page allocator (resend)
On Thu, Jul 16, 2009 at 12:14:13PM -0700, David Rientjes wrote:
> 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).

Ok, lets go with this patch then. Thanks

> ---
> 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,
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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