linux-kernel - Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc

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Date:	Thu, 02 Jul 2009 08:49:51 +0800
From:	Shan Wei <shanwei@...fujitsu.com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in
 cfq_find_alloc_queue()

Jens Axboe said:
> On Wed, Jul 01 2009, Shan Wei wrote:
>> Jens Axboe said:
>>> Setup an emergency fallback cfqq that we allocate at IO scheduler init
>>> time. If the slab allocation fails in cfq_find_alloc_queue(), we'll just
>>> punt IO to that cfqq instead. This ensures that cfq_find_alloc_queue()
>>> never fails without having to ensure free memory.
>>>
>>> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
>>> ---
>>>  
>>> @@ -1740,11 +1745,8 @@ cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct io_context *ioc,
>>>  		cfqq = *async_cfqq;
>>>  	}
>>>  
>>> -	if (!cfqq) {
>>> +	if (!cfqq)
>>>  		cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);
>>> -		if (!cfqq)
>>> -			return NULL;
>>> -	}
>> I jsut reviewed the code and found that the check of cfqq is also redundant
>> after doing cfq_get_queue() in cfq_set_request.
>>
>> The patch is based on Linus's main tree. 
> 
> It's not redundant in Linus' tree, cfq_get_queue() can return NULL for
> != __GFP_WAIT.
> 

Yes. So, the patch is only for "for-linus" branch of your tree, not for Linus's tree.

I noticed the patch is in your tree now, thanks.

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