On Mon, Oct 21 2013 at 2:06pm -0400, Christoph Hellwig <hch@infradead.org> wrote: > On Mon, Oct 21, 2013 at 11:01:29AM -0400, Mike Snitzer wrote: > > It isn't DM that splits the IO into 4K chunks; it is the VM subsystem > > no? > > Well, it's the block layer based on what DM tells it. Take a look at > dm_merge_bvec > > >From dm_merge_bvec: > > /* > * If the target doesn't support merge method and some of the devices > * provided their merge_bvec method (we know this by looking at > * queue_max_hw_sectors), then we can't allow bios with multiple vector > * entries. So always set max_size to 0, and the code below allows > * just one page. > */ > > Although it's not the general case, just if the driver has a > merge_bvec method. But this happens if you using DM ontop of MD where I > saw it aswell as on rbd, which is why it's correct in this context, too. Right, but only if the DM target that is being used doesn't have a .merge method. I don't think it was ever shared which DM target is in use here.. but both the linear and stripe DM targets provide a .merge method. > Sorry for over generalizing a bit. No problem. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
