Re: dm-crypt parallelization patches

[Vivek Goyal]

On Tue, Apr 09, 2013 at 04:32:28PM -0400, Mikulas Patocka wrote:

[..]
> Generally, we shouldn't associate bios with "current" task in device 
> mapper targets. For example suppose that we have two stacked dm-crypt 
> targets:
>
> In the "current" process pointer in lower dm-crypt target's request 
> function always points to the workqueue of the upper dm-crypt target that 
> submits the bios. So if we associate the bio with "current" in the lower 
> target, we are associating it with a preallocated workqueue and we already 
> lost the information who submitted it.
> 
> You should associate a bio with a task when you create the bio and "md" 
> and "dm" midlayers should just forward this association to lower layer 
> bios.

bio_associate_current() return -EBUSY if bio has already been associated
with an io context.

So in a stack if every driver calls bio_associate_current(), upon bio
submission, it will automatically amke sure bio gets associated with
submitter task in top level device and calls by lower level device
will be ignored.

Lower level devices I think just need to make sure this context
info is propogated to cloned bios.


[..]
> +#ifdef CONFIG_BLK_CGROUP
> +	tio->clone.bi_ioc = ci->bio->bi_ioc;
> +	tio->clone.bi_css = ci->bio->bi_css;

You also need to take references to ioc and css objects. I guess a helper
function will be better. May be something like.

bio_associate_bio_context(bio1, bio2)

And this initialize bio2's context with bio1's context.

Thanks
Vivek
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