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

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Date:	Fri, 01 Jun 2012 13:22:15 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Nathan Zimmer <nzimmer@....com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, 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

(6/1/12 10:24 AM), Nathan Zimmer wrote:
> 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.

yes, and it is bug source. we may need to change soon. I guess the right way is
to make vm_ops->interleave and interleave_nid uses it if povided.

btw, I don't think node_random() is good idea. it is random(pid + jiffies + cycle).
current->cpuset_mem_spread_rotor is per-thread value. but you now need per-inode
interleave offset. maybe, just inode addition is enough. Why do you need randomness?


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