linux-kernel - Re: [PATCH v2] tmpfs not interleaving properly

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Message-ID: <20120601142437.GA13739@gulag1.americas.sgi.com>
Date:	Fri, 1 Jun 2012 09:24:37 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nathan Zimmer <nzimmer@....com>, hughd@...gle.com,
	npiggin@...il.com, cl@...ux.com, lee.schermerhorn@...com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	stable@...r.kernel.org, riel@...hat.com
Subject: Re: [PATCH v2] tmpfs not interleaving properly

On Thu, May 31, 2012 at 04:35:53PM -0400, KOSAKI Motohiro wrote:
> (5/31/12 4:25 PM), Andrew Morton wrote:
>> On Thu, 31 May 2012 16:09:15 -0400
>> KOSAKI Motohiro<kosaki.motohiro@...il.com>  wrote:
>>
>>>> --- a/mm/shmem.c
>>>> +++ b/mm/shmem.c
>>>> @@ -929,7 +929,7 @@ static struct page *shmem_alloc_page(gfp_t gfp,
>>>>    	/*
>>>>    	 * alloc_page_vma() will drop the shared policy reference
>>>>    	 */
>>>> -	return alloc_page_vma(gfp,&pvma, 0);
>>>> +	return alloc_page_vma(gfp,&pvma, info->node_offset<<   PAGE_SHIFT );
>>>
>>> 3rd argument of alloc_page_vma() is an address. This is type error.
>>
>> Well, it's an unsigned long...
>>
>> But yes, it is conceptually wrong and *looks* weird.  I think we can
>> address that by overcoming our peculair aversion to documenting our
>> code, sigh.  This?
>
> Sorry, no.
>
> addr agrument of alloc_pages_vma() have two meanings.
>
> 1) interleave node seed
> 2) look-up key of shmem policy
>
> I think this patch break (2). shmem_get_policy(pol, addr) assume caller honor to
> pass correct address.

But the pseudo vma we generated in shmem_alloc_page the vm_ops are set to NULL.
So get_vma_policy will return the policy provided by the pseudo vma and not reach
the shmem_get_policy.

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