linux-kernel - Re: [PATCH 15/18] z2ram: dequeue in-flight request

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Date:	Sat, 16 May 2009 16:54:56 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, rusty@...tcorp.com.au,
	James.Bottomley@...senPartnership.com, mike.miller@...com,
	donari75@...il.com, paul.clements@...eleye.com, tim@...erelk.net,
	Geert.Uytterhoeven@...ycom.com, davem@...emloft.net,
	Laurent@...vier.info, jgarzik@...ox.com, jeremy@...source.com,
	grant.likely@...retlab.ca, adrian@...en.demon.co.uk,
	sfr@...b.auug.org.au, bzolnier@...il.com, petkovbb@...glemail.com,
	oakad@...oo.com, drzeus@...eus.cx, dwmw2@...radead.org,
	Markus.Lidel@...dowconnect.com, wein@...ibm.com,
	schwidefsky@...ibm.com, zaitcev@...hat.com,
	fujita.tomonori@....ntt.co.jp, axboe@...nel.dk
Subject: Re: [PATCH 15/18] z2ram: dequeue in-flight request

Hello.

Tejun Heo wrote:

> z2ram processes requests one-by-one synchronously and can be easily
> converted to dequeueing model.  Convert it.
>
> [ Impact: dequeue in-flight request ]
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>  drivers/block/z2ram.c |   19 +++++++++++++++----
>  1 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/z2ram.c b/drivers/block/z2ram.c
> index 6a13838..c909c1a 100644
> --- a/drivers/block/z2ram.c
> +++ b/drivers/block/z2ram.c
> @@ -70,15 +70,21 @@ static struct gendisk *z2ram_gendisk;
>  static void do_z2_request(struct request_queue *q)
>  {
>  	struct request *req;
> -	while ((req = elv_next_request(q)) != NULL) {
> +
> +	req = elv_next_request(q);
> +	if (req)
> +		blkdev_dequeue_request(req);
> +
> +	while (req) {
>  		unsigned long start = blk_rq_pos(req) << 9;
>  		unsigned long len  = blk_rq_cur_bytes(req);
> +		int err = 0;
>  
>  		if (start + len > z2ram_size) {
>  			printk( KERN_ERR DEVICE_NAME ": bad access: block=%lu, count=%u\n",
>  				blk_rq_pos(req), blk_rq_cur_sectors(req));
> -			__blk_end_request_cur(req, -EIO);
> -			continue;
> +			err = -EIO;
> +			goto done;
>  		}
>  		while (len) {
>  			unsigned long addr = start & Z2RAM_CHUNKMASK;
> @@ -93,7 +99,12 @@ static void do_z2_request(struct request_queue *q)
>  			start += size;
>  			len -= size;
>  		}
> -		__blk_end_request_cur(req, 0);
> +	done:
> +		if (!__blk_end_request_cur(req, err)) {
> +			req = elv_next_request(q);
> +			if (req)
> +				blkdev_dequeue_request(req);
> +		}
>  	}
>  }
>   

   I'm sure this can be made more compact and without duplication (in 
many other cases as well):

@@ -70,15 +70,21 @@ static struct gendisk *z2ram_gendisk;

 static void do_z2_request(struct request_queue *q)
 {
 	struct request *req;
+
 	while ((req = elv_next_request(q)) != NULL) {
 		unsigned long start = blk_rq_pos(req) << 9;
 		unsigned long len  = blk_rq_cur_bytes(req);
 
+		blkdev_dequeue_request(req);
+
 		if (start + len > z2ram_size) {
 			printk( KERN_ERR DEVICE_NAME ": bad access: block=%lu, count=%u\n",
 				blk_rq_pos(req), blk_rq_cur_sectors(req));
-			__blk_end_request_cur(req, -EIO);
-			continue;
+			err = -EIO;
+			goto done;
 		}
 		while (len) {
 			unsigned long addr = start & Z2RAM_CHUNKMASK;
@@ -93,7 +99,12 @@ static void do_z2_request(struct request_queue *q)
 			start += size;
 			len -= size;
 		}
-		__blk_end_request_cur(req, 0);
+	done:
+		if (__blk_end_request_cur(req, err));
+			break;
 	}
 }


MBR, Sergei


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