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

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Hello, I wrote:

   Oops, sent this message only to Tejun before, so have to repost now...

>> 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@kernel.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);

  Oops, missed:

+         int err;
+
>
> +        blkdev_dequeue_request(req);
> +

+again:

>         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);
+            err = 0;
> +    done:
> +        if (__blk_end_request_cur(req, err));
> +            break;

  Oops, should've been:

+            if (__blk_end_request_cur(req, err))
+                goto again;

>     }
> }

  It can also be:

@@ -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) {
+    while (1) {
+        struct request *req = elv_next_request(q);
+        unsigned long start, len;
+        int err;
+
+        if (req == NULL)
+            break;
+
+        blkdev_dequeue_request(req);
+
+again:
+        start = blk_rq_pos(req) << 9;
+        len = blk_rq_cur_bytes(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);
+        err = 0;
+    done:
+        if (__blk_end_request_cur(req, err))
+            goto again;
    }
}


if you want to get rid of the assignement in the *while* statement...

MBR, Sergei