On Tue, May 26, 2015 at 7:36 AM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Fri, May 22 2015 at 2:18pm -0400, > Ming Lin <mlin@xxxxxxxxxx> wrote: > >> From: Kent Overstreet <kent.overstreet@xxxxxxxxx> >> >> The way the block layer is currently written, it goes to great lengths >> to avoid having to split bios; upper layer code (such as bio_add_page()) >> checks what the underlying device can handle and tries to always create >> bios that don't need to be split. >> >> But this approach becomes unwieldy and eventually breaks down with >> stacked devices and devices with dynamic limits, and it adds a lot of >> complexity. If the block layer could split bios as needed, we could >> eliminate a lot of complexity elsewhere - particularly in stacked >> drivers. Code that creates bios can then create whatever size bios are >> convenient, and more importantly stacked drivers don't have to deal with >> both their own bio size limitations and the limitations of the >> (potentially multiple) devices underneath them. In the future this will >> let us delete merge_bvec_fn and a bunch of other code. > > This series doesn't take any steps to train upper layers > (e.g. filesystems) to size their bios larger (which is defined as > "whatever size bios are convenient" above). > > bio_add_page(), and merge_bvec_fn, served as the means for upper layers > (and direct IO) to build up optimally sized bios. Without a replacement > (that I can see anyway) how is this patchset making forward progress > (getting Acks, etc)!? > > I like the idea of reduced complexity associated with these late bio > splitting changes I'm just not seeing how this is ready given there are > no upper layer changes that speak to building larger bios.. > > What am I missing? See: [PATCH v4 02/11] block: simplify bio_add_page() https://lkml.org/lkml/2015/5/22/754 Now bio_add_page() can build lager bios. And blk_queue_split() can split the bios in ->make_request() if needed. Thanks. > > Please advise, thanks! > Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
