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:	Wed, 1 Jul 2009 11:32:35 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Shan Wei <shanwei@...fujitsu.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()

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.


> 
> Signed-off-by: Shan Wei <shanwei@...fujitsu.com>
> ---
>  block/cfq-iosched.c |    4 ----
>  1 files changed, 0 insertions(+), 4 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 833ec18..c373237 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2307,10 +2307,6 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
>  	cfqq = cic_to_cfqq(cic, is_sync);
>  	if (!cfqq) {
>  		cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
> -
> -		if (!cfqq)
> -			goto queue_fail;
> -
>  		cic_set_cfqq(cic, cfqq, is_sync);
>  	}
>  

-- 
Jens Axboe

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