[PATCH] Do not trigger OOM-killer for high-order allocation failures

[PATCH] Do not trigger OOM-killer for high-order allocation failures

[Mel Gorman]

out_of_memory() may be called when an allocation is failing and the direct
reclaim is not making any progress. This does not take into account the
requested order of the allocation. If the request if for an order larger
than PAGE_ALLOC_COSTLY_ORDER, it is reasonable to fail the allocation
because the kernel makes no guarantees about those allocations succeeding.

This false OOM situation can occur if a user is trying to grow the hugepage
pool in a script like;

#!/bin/bash
REQUIRED=$1
echo 1 > /proc/sys/vm/hugepages_treat_as_movable
echo $REQUIRED > /proc/sys/vm/nr_hugepages
ACTUAL=`cat /proc/sys/vm/nr_hugepages`
while [ $REQUIRED -ne $ACTUAL ]; do
	echo Huge page pool at $ACTUAL growing to $REQUIRED
	echo $REQUIRED > /proc/sys/vm/nr_hugepages
	ACTUAL=`cat /proc/sys/vm/nr_hugepages`
	sleep 1
done

This is a reasonable scenario when ZONE_MOVABLE is in use but triggers OOM
easily on 2.6.23-rc1. This patch will fail an allocation for an order above
PAGE_ALLOC_COSTLY_ORDER instead of killing processes and retrying.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>

---
 page_alloc.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 40954fb..da57173 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1350,6 +1350,10 @@ nofail_alloc:
 		if (page)
 			goto got_pg;
 
+		/* The OOM killer will not help higher order allocs so fail */
+		if (order > PAGE_ALLOC_COSTLY_ORDER)
+			goto nopage;
+
 		out_of_memory(zonelist, gfp_mask, order);
 		goto restart;
 	}
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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Re: [PATCH] Do not trigger OOM-killer for high-order allocation failures

[Andy Whitcroft]

Mel Gorman wrote:
> out_of_memory() may be called when an allocation is failing and the direct
> reclaim is not making any progress. This does not take into account the
> requested order of the allocation. If the request if for an order larger
> than PAGE_ALLOC_COSTLY_ORDER, it is reasonable to fail the allocation
> because the kernel makes no guarantees about those allocations succeeding.
> 
> This false OOM situation can occur if a user is trying to grow the hugepage
> pool in a script like;
> 
> #!/bin/bash
> REQUIRED=$1
> echo 1 > /proc/sys/vm/hugepages_treat_as_movable
> echo $REQUIRED > /proc/sys/vm/nr_hugepages
> ACTUAL=`cat /proc/sys/vm/nr_hugepages`
> while [ $REQUIRED -ne $ACTUAL ]; do
> 	echo Huge page pool at $ACTUAL growing to $REQUIRED
> 	echo $REQUIRED > /proc/sys/vm/nr_hugepages
> 	ACTUAL=`cat /proc/sys/vm/nr_hugepages`
> 	sleep 1
> done
> 
> This is a reasonable scenario when ZONE_MOVABLE is in use but triggers OOM
> easily on 2.6.23-rc1. This patch will fail an allocation for an order above
> PAGE_ALLOC_COSTLY_ORDER instead of killing processes and retrying.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>

We have had this problem for a long time.  When allocating large pages
we could find ourselves unable to allocate such a page nor reclaim one
for ourselves.  At this point we will OOM with little hope of that
actually changing the situation for the better.

As you say PAGE_ALLOC_COSTLY_ORDER pretty much defines the orders at
which any sort of guarantee of success is provided.  It seems preferable
to fail a allocations above this order/ than killing things to try and
make it available.  As higher order users already have to handle failure
to allocate they should be best equipped to continue.

Acked-by: Andy Whitcroft <apw@shadowen.org>

> ---
>  page_alloc.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 40954fb..da57173 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1350,6 +1350,10 @@ nofail_alloc:
>  		if (page)
>  			goto got_pg;
>  
> +		/* The OOM killer will not help higher order allocs so fail */
> +		if (order > PAGE_ALLOC_COSTLY_ORDER)
> +			goto nopage;
> +
>  		out_of_memory(zonelist, gfp_mask, order);
>  		goto restart;
>  	}

-apw

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