Hi Christoph, Thank you for your comments! > From: Christoph Hellwig, Sent: Wednesday, June 5, 2019 9:38 PM > > On Wed, Jun 05, 2019 at 01:21:59PM +0100, Robin Murphy wrote: > > And if the problem is really that you're not getting merging because of > > exposing the wrong parameters to the DMA API and/or the block layer, or > > that you just can't quite express your requirement to the block layer in > > the first place, then that should really be tackled at the source rather > > than worked around further down in the stack. > > The problem is that we need a way to communicate to the block layer > that more than a single segment is ok IFF the DMA API instance supports > merging. And of course the answer will depend on futher parameters > like the maximum merged segment size and alignment for the segement. I'm afraid but I don't understand why we need a way to communicate to the block layer that more than a single segment is ok IFF the DMA API instance supports merging. > We'll need some way to communicate that, but I don't really think this > is series is the way to go. I should discard the patches 1/8 through 4/8. > We'd really need something hanging off the device (or through a query > API) how the dma map ops implementation exposes under what circumstances > it can merge. The driver can then communicate that to the block layer > so that the block layer doesn't split requests up when reaching the > segement limit. The block layer already has a limit "max_segment_size" for each device so that regardless it can/cannot merge the segments, we can use the limit. Is my understanding incorrect? Best regards, Yoshihiro Shimoda
