On Mon, Oct 31, 2016 at 08:39:15AM -0700, Christoph Hellwig wrote: > On Sat, Oct 29, 2016 at 04:08:27PM +0800, Ming Lei wrote: > > Some drivers(such as dm) should be capable of dealing with multipage > > bvec, but the incoming bio may be too big, such as, a new singlepage bvec > > bio can't be cloned from the bio, or can't be allocated to singlepage > > bvec with same size. > > > > At least crypt dm, log writes and bcache have this kind of issue. > > We already have the segment_size limitation for request based drivers. > I'd rather extent it to bio drivers if really needed. > > But then again we should look into not having this limitation. E.g. > for bcache I'd be really surprised if it's that limited, given that > Kent came up with this whole multipage bvec scheme. AFAIK the only issue is with drivers that may have to bounce bios - pages that were contiguous in the original bio won't necessarily be contiguous in the bounced bio, thus bouncing might require more than BIO_MAX_SEGMENTS bvecs. I don't know what Ming's referring to by "singlepage bvec bios". Anyways, bouncing comes up in multiple places so we probably need to come up with a generic solution for that. Other than that, there shouldn't be any issues or limitations - if you're not bouncing, there's no need to clone the bvecs. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
