Re: [dm-devel] [PATCH v3 14/16] Gut bio_add_page()

[Kent Overstreet <koverstreet google com>]

On Tue, May 29, 2012 at 11:54:38AM +1000, Dave Chinner wrote:
> It also allowed us to build IOs that span
> entire RAID stripe widths, thereby avoiding potential RAID RMW
> cycles, and even allowing high end raid controllers to trigger BBWC
> bypass fast paths that could double or triple the write throughput
> of the arrays...

merge_bvec_fn has nothing to do with that though, since for one there
aren't any merge_bvec_fn's being called in the IO paths on these high
end disk arrays, and for our software raid implementations their
merge_bvec_fns will keep you from sending them bios that span entire
stripes.