On Thu, Jun 15, 2017 at 2:35 PM, Andreas Dilger <adilger@xxxxxxxxx> wrote: > >> On Jun 15, 2017, at 7:07 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote: >> >> On Thu, Jun 15, 2017 at 4:15 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >>> On Wed, Jun 14, 2017 at 01:06:53PM -0400, Olga Kornievskaia wrote: >>>> This is a proposal to allow 64bit count to copy and return as >>>> a result of a copy_file_range. No attempt was made to share code >>>> with the 32bit function because 32bit interface should probably >>>> get depreciated. >>>> >>>> Why use 64bit? Current uses of 32bit are by clone_file_range() >>>> which could use 64bit count and NFS copy_file_range also supports >>>> 64bit count value. >>> >>> Please provide a very good use case that actually matters to a large >>> portion of the Linux users. >> >> Reason: it will not hurt any user but it will help for >> server-to-server NFS copy because for each invocation of of >> copy_file_range() it requires that the client sends COPY_NOTIFY, then >> COPY and then a copy triggers a establishment of clientid/session >> before the reading of the source file can happen. All that could be >> saved by have a 64bit value. > > What is the overhead of sending a couple of RPCs vs. copying 4GB of > data on the server? We get about 11% improvement having an interface that removes the need for multiple calls. That's testing 8gb copy that normally would have needed 2 copies. >> Current copy_file_range would work for any file size, it would just >> need to be called in a loop by the application. With the given >> proposal, there wouldn't be a need for the application to loop due to >> the API size limitation. It might still loop if a partial copy was >> done. > > > Given that there always needs to be a loop to handle partial completion, > adding the 64-bit syscall doesn't really simplify the application at > all, but adds duplicate code to the kernel for little benefit. If 32bit version would be deprecated then there won't be duplicate code.
