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 <[EMAIL PROTECTED]>
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 <[EMAIL PROTECTED]> > --- > 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
