Messages in this thread | | | Date | Sun, 06 Oct 2013 03:42:35 -0500 | From | Rob Landley <> | Subject | Re: [RFC] extending splice for copy offloading |
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On 09/26/2013 01:06:41 PM, Miklos Szeredi wrote: > On Thu, Sep 26, 2013 at 5:34 PM, J. Bruce Fields > <bfields@fieldses.org> wrote: > > On Thu, Sep 26, 2013 at 10:58:05AM +0200, Miklos Szeredi wrote: > >> On Wed, Sep 25, 2013 at 11:07 PM, Zach Brown <zab@redhat.com> > wrote: > >> >> A client-side copy will be slower, but I guess it does have the > >> >> advantage that the application can track progress to some > degree, and > >> >> abort it fairly quickly without leaving the file in a totally > undefined > >> >> state--and both might be useful if the copy's not a simple > constant-time > >> >> operation. > >> > > >> > I suppose, but can't the app achieve a nice middle ground by > copying the > >> > file in smaller syscalls? Avoid bulk data motion back to the > client, > >> > but still get notification every, I dunno, few hundred meg? > >> > >> Yes. And if "cp" could just be switched from a read+write syscall > >> pair to a single splice syscall using the same buffer size. > > > > Will the various magic fs-specific copy operations become > inefficient > > when the range copied is too small? > > We could treat spice-copy operations just like write operations (can > be buffered, coalesced, synced). > > But I'm not sure it's worth the effort; 99% of the use of this > interface will be copying whole files.
My "patch" implementation (in busybox and toybox) hits a point where it wants to copy the rest of the file, once there are no more hunks to apply. This is not copying a whole file. A similar thing happens with tail when you use the +N syntax to skip start instead of end lines. I can see sed doing a similar thing when told to operate on line ranges...
Note sure your 99% holds up here.
Rob
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