On Mon, Jan 13, 2020 at 03:00:40PM -0700, Jens Axboe wrote:
> On 1/13/20 2:58 PM, Matthew Wilcox wrote:
> > On Mon, Jan 13, 2020 at 06:00:52PM +0000, Chris Mason wrote:
> >> This is true, I didn't explain that part well ;) Depending on
> >> compression etc we might end up poking the xarray inside the actual IO
> >> functions, but the main difference is that btrfs is building a single
> >> bio. You're moving the plug so you'll merge into single bio, but I'd
> >> rather build 2MB bios than merge them.
> >
> > Why don't we store a bio pointer inside the plug? You're opencoding that,
> > iomap is opencoding that, and I bet there's a dozen other places where
> > we pass a bio around. Then blk_finish_plug can submit the bio.
>
> Plugs aren't necessarily a bio, they can be callbacks too.
I'm thinking something as simple as this:
@@ -1711,6 +1711,7 @@ void blk_start_plug(struct blk_plug *plug)
INIT_LIST_HEAD(&plug->mq_list);
INIT_LIST_HEAD(&plug->cb_list);
+ plug->bio = NULL;
plug->rq_count = 0;
plug->multiple_queues = false;
@@ -1786,6 +1787,8 @@ void blk_finish_plug(struct blk_plug *plug)
{
if (plug != current->plug)
return;
+ if (plug->bio)
+ submit_bio(plug->bio);
blk_flush_plug_list(plug, false);
current->plug = NULL;
@@ -1160,6 +1160,7 @@ extern void blk_set_queue_dying(struct request_queue *);
struct blk_plug {
struct list_head mq_list; /* blk-mq requests */
struct list_head cb_list; /* md requires an unplug callback */
+ struct bio *bio;
unsigned short rq_count;
bool multiple_queues;
};
with accessors to 'get_current_bio()' and 'set_current_bio()'.
