Messages in this thread | | | Subject | Re: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP_NOFAIL | From | Peter Zijlstra <> | Date | Tue, 12 May 2009 07:39:55 +0200 |
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On Mon, 2009-05-11 at 15:11 -0700, Andrew Morton wrote: > On Mon, 11 May 2009 14:45:18 -0700 (PDT) > David Rientjes <rientjes@google.com> wrote: > > > On Mon, 11 May 2009, Andrew Morton wrote: > > > > > > The oom killer must be invoked regardless of the order if the allocation > > > > is __GFP_NOFAIL, otherwise it will loop forever when reclaim fails to > > > > free some memory. > > > > > > We should discourage callers from using __GFP_NOFAIL at all. We should > > > electrocute callers for using __GFP_NOFAIL on large allocations. How's about > > > > > > WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER && > > > (gfp_mask & __GFP_NOFAIL)); > > > or, preferably: > > > > > > WARN_ON_ONCE(order > 0 && (gfp_mask & __GFP_NOFAIL)); > > > > > > > Not sure it would help since the oom killer will be now be called for such > > an allocation and that dumps the stack (and will actually show the order > > and gfp flags as well). > > No, the intent of that warning is to find all call sites which use > __GFP_NOFAIL on order>0 so we can hunt down and eliminate them. > > > please review...
Fully agreed, people should use banker's algorithm to guarantee progress, not create deadlocks with inf loops.
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> From: Andrew Morton <akpm@linux-foundation.org> > > __GFP_NOFAIL is a bad fiction. Allocations _can_ fail, and callers should > detect and suitably handle this (and not by lamely moving the infinite > loop up to the caller level either). > > Attempting to use __GFP_NOFAIL for a higher-order allocation is even > worse, so add a once-off runtime check for this to slap people around for > even thinking about trying it. > > Cc: David Rientjes <rientjes@google.com> > Cc: Mel Gorman <mel@csn.ul.ie> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > mm/page_alloc.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff -puN mm/page_alloc.c~a mm/page_alloc.c > --- a/mm/page_alloc.c~a > +++ a/mm/page_alloc.c > @@ -1201,8 +1201,19 @@ static int should_fail_alloc_page(gfp_t > { > if (order < fail_page_alloc.min_order) > return 0; > - if (gfp_mask & __GFP_NOFAIL) > + if (gfp_mask & __GFP_NOFAIL) { > + /* > + * __GFP_NOFAIL is not to be used in new code. > + * > + * All __GFP_NOFAIL callers should be fixed so that they > + * properly detect and handle allocation failures. > + * > + * We most definitely don't want callers attempting to allocate > + * greater than single-page units with __GFP_NOFAIL. > + */ > + WARN_ON_ONCE(order > 0); > return 0; > + } > if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM)) > return 0; > if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & __GFP_WAIT)) > _ > >
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