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

[Sergei Shtylyov]

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@xxxxxxxxxx>
> > ---
> >  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


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