Re: [PATCH] block: flush queued bios when the process blocks

[Jens Axboe]

On 2014-05-27 09:23, Mikulas Patocka wrote:
> On Tue, 27 May 2014, Jens Axboe wrote:
>
> > On 2014-05-27 09:03, Mikulas Patocka wrote:
> > > The block layer uses per-process bio list to avoid recursion in
> > > generic_make_request. When generic_make_request is called recursively, the
> > > bio is added to current->bio_list and the function returns immediatelly.
> > > The top-level instance of generic_make_requests takes bios from
> > > current->bio_list and processes them.
> >
> > This really begs the question of why we just don't use the per-process plugs
> > for this. We already have scheduler hooks in place to flush those at the
> > appropriate time. Why are we reinventing something for essentially the same
> > thing?
> >
> > --
> > Jens Axboe
>
> Plugs work with requests, this patch works with bios. They are different
> structures, so you can't use one infrastructure to process them.

Yes... I realize the list and plugs are for requests. But there's 
nothing preventing a non-rq hook, we have uses like that too. And it 
could easily be extended to handle bio lists, too.

> The patch adds bio list flushing to the scheduler just besides plug
> flushsing.

... which is exactly why I'm commenting. It'd be great to avoid yet one 
more scheduler hook for this sort of thing.

--
Jens Axboe

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