linux-kernel - Re: [3.7-rc6] capture_free_page() frees page without accounting for them??

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Message-ID: <50AC24F5.9090303@linux.vnet.ibm.com>
Date:	Tue, 20 Nov 2012 16:48:53 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [3.7-rc6] capture_free_page() frees page without accounting for
 them??

I'm really evil, so I changed the loop in compact_capture_page() to
basically steal the highest-order page it can.  This shouldn't _break_
anything, but it does ensure that we'll be splitting pages that we find
more often and recreating this *MUCH* faster:

-               for (order = cc->order; order < MAX_ORDER; order++) {
+               for (order = MAX_ORDER - 1; order >= cc->order;order--)

I also augmented the area in capture_free_page() that I expect to be
leaking:

        if (alloc_order != order) {
                static int leaked_pages = 0;
                leaked_pages += 1<<order;
                leaked_pages -= 1<<alloc_order;
                printk("%s() alloc_order(%d) != order(%d) leaked %d\n",
                                __func__, alloc_order, order,
				leaked_pages);
                expand(zone, page, alloc_order, order,
                        &zone->free_area[order], migratetype);
        }

I add up all the fields in buddyinfo to figure out how much _should_ be
in the allocator and then compare it to MemFree to get a guess at how
much is leaked.  That number correlates _really_ well with the
"leaked_pages" variable above.  That pretty much seals it for me.

I'll run a stress test overnight to see if it pops up again.  The patch
I'm running is attached.  I'll send a properly changelogged one tomorrow
if it works.

View attachment "leak-fix-20121120-1.patch" of type "text/x-patch" (667 bytes)