On Fri, Feb 15, 2019 at 03:00:31PM -0700, Jason Gunthorpe wrote: > On Fri, Feb 15, 2019 at 06:31:36PM +0000, Christopher Lameter wrote: > > On Fri, 15 Feb 2019, Matthew Wilcox wrote: > > > > > > Since RDMA is something similar: Can we say that a file that is used for > > > > RDMA should not use the page cache? > > > > > > That makes no sense. The page cache is the standard synchronisation point > > > for filesystems and processes. The only problems come in for the things > > > which bypass the page cache like O_DIRECT and DAX. > > > > It makes a lot of sense since the filesystems play COW etc games with the > > pages and RDMA is very much like O_DIRECT in that the pages are modified > > directly under I/O. It also bypasses the page cache in case you have > > not noticed yet. > > It is quite different, O_DIRECT modifies the physical blocks on the > storage, bypassing the memory copy. >
Really? I thought O_DIRECT allowed the block drivers to write to/from user space buffers. But the _storage_ was still under the control of the block drivers? > > RDMA modifies the memory copy. > > pages are necessary to do RDMA, and those pages have to be flushed to > disk.. So I'm not seeing how it can be disconnected from the page > cache? I don't disagree with this. Ira > > Jason
