linux-kernel - Re: 2.6.38 page

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Message-ID: <20110414215327.GI11871@csn.ul.ie>
Date:	Thu, 14 Apr 2011 22:53:27 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	raz ben yehuda <raziebe@...il.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>, riel@...hat.com,
	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org
Subject: Re: 2.6.38 page_test regression

On Thu, Apr 14, 2011 at 11:07:23PM +0300, raz ben yehuda wrote:
> bah. Mel is correct. I did mean page_test  ( in my defense it is in the
> msg ).
> Here some more information:
> 1. I manage to lower the regression to 2 sha1's:
>     	32dba98e085f8b2b4345887df9abf5e0e93bfc12 to
> 71e3aac0724ffe8918992d76acfe3aad7d8724a5. 
> 	though I had to remark wait_split_huge_page for the sake of
> compilation. up to 32dba98e085f8b2b4345887df9abf5e0e93bfc12 there is no
> regression.
> 
> 2. I booted 2.6.37-rc5 you gave me. same regression is there. 

Extremely long shot - try this patch.

diff --git a/mm/memory.c b/mm/memory.c
index c50a195..a39baaf 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3317,7 +3317,7 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * run pte_offset_map on the pmd, if an huge pmd could
 	 * materialize from under us from a different thread.
 	 */
-	if (unlikely(__pte_alloc(mm, vma, pmd, address)))
+	if (unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, vma, pmd, address))
 		return VM_FAULT_OOM;
 	/* if an huge pmd materialized from under us just retry later */
 	if (unlikely(pmd_trans_huge(*pmd)))
--
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