[dm-devel] dm-crypt: Fix error with too large bios

[Mike Snitzer]

On Thu, Aug 25 2016 at  4:13pm -0400,
Jens Axboe <axboe at kernel.dk> wrote:

> On 08/25/2016 12:34 PM, Mikulas Patocka wrote:
> >
> >Device mapper can't split the bio in generic_make_request - it frees the
> >md->queue->bio_split bioset, to save one kernel thread per device. Device
> >mapper uses its own splitting mechanism.
> >
> >So what is the final decision? - should device mapper split the big bio or
> >should bcache not submit big bios?
> >
> >I think splitting big bios in the device mapper is better - simply because
> >it is much less code than reworking bcache to split bios internally.
> >
> >BTW. In the device mapper, we have a layer dm-io, that was created to work
> >around bio size limitations - it accepts unlimited I/O request and splits
> >it to several bios. When bio size limitations are gone, we could simplify
> >dm-io too.
> 
> The patch from Ming Lei was applied for 4.8 the other day.

See linux-block commit:
4d70dca4eadf2f block: make sure a big bio is split into at most 256 bvecs
http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=4d70dca4eadf2f95abe389116ac02b8439c2d16c