Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue()

[Shan Wei <shanwei@cn.fujitsu.com>]

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@oracle.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. 

Signed-off-by: Shan Wei <shanwei@cn.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);
 	}