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SubjectRe: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP_NOFAIL
On Mon, 11 May 2009 15:31:04 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Mon, 11 May 2009, Andrew Morton wrote:
>
> > __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>
>
> This only emits a warning when you have CONFIG_DEBUG_KERNEL,
> CONFIG_FAULT_INJECTION, and CONFIG_FAIL_PAGE_ALLOC, which is all related
> to fault injection (since we never want to inject a fault into anything
> using __GFP_NOFAIL). So it may be helpful in tracking down such callers,
> but is unrelated to the config options that enable it and it may not get
> the best coverage.

oh, well that was pretty useless then. I was trying to find a handy
spot where we can avoid adding fastpath cycles.

How about we sneak it into the order>0 leg inside buffered_rmqueue()?


--- a/mm/page_alloc.c~page-allocator-warn-if-__gfp_nofail-is-used-for-a-large-allocation
+++ a/mm/page_alloc.c
@@ -1130,6 +1130,20 @@ again:
list_del(&page->lru);
pcp->count--;
} else {
+ if (unlikely(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;
+ }
spin_lock_irqsave(&zone->lock, flags);
page = __rmqueue(zone, order, migratetype);
__mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << order));
_


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