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

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Message-ID: <4FE14B4D.2000205@gmail.com>
Date:	Wed, 20 Jun 2012 00:02:21 -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

(6/19/12 7:21 PM), Nathan Zimmer wrote:
> On Fri, Jun 01, 2012 at 01:22:15PM -0400, KOSAKI Motohiro wrote:
>> (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.
> 
> If we provide vm_ops then won't shmem_get_policy get called?
> That would be an issue since shmem_get_policy assumes vm_file is non NULL.
>
>> 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?
> 
> I don't really need the randomness, the rotor should be good enough.
> The correct way to get that is cpuset_mem_spread_node(), yes?

I think that's good idea too.
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