linux-kernel - Re: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP

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Date:	Mon, 11 May 2009 15:46:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	gregkh@...e.de, npiggin@...e.de, mel@....ul.ie,
	a.p.zijlstra@...llo.nl, cl@...ux-foundation.org,
	dave@...ux.vnet.ibm.com, san@...roid.com, arve@...roid.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP_NOFAIL

On Mon, 11 May 2009 15:31:04 -0700 (PDT)
David Rientjes <rientjes@...gle.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@...gle.com>
> > Cc: Mel Gorman <mel@....ul.ie>
> > Signed-off-by: Andrew Morton <akpm@...ux-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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