Re: [PATCH 0/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2

On Mon, 1 Jun 2026 18:33:25 +0100
Al Viro <[email protected]> wrote:

> On Mon, Jun 01, 2026 at 10:17:23AM -0700, Linus Torvalds wrote:
> 
> > TLDR: maybe we could ghet rid of "f_op->splice_read". *That* would be
> > a big simplification.  
> 
> FUSE might be interesting - fuse_dev_splice_read() and its ilk.
> Communications between the kernel and fuse server at least used to
> seriously want that, so that would be one place to look for unhappy
> userland...
> 
> splice-related logics in fs/fuse/dev.c is interesting; another place
> like this is kernel/trace/, but I'm less familiar with that one.
> 
> rostedt Cc'd (miklos already had been)

Thanks for the Cc. The tracing ring buffer was specifically made to be used
by splice and the libtracefs has a lot of code to use it as well. As
reading the ring buffer literally swaps out the write portion with a blank
read portion, that portion (sub-buffer) is used to be directly fed into
splice, providing a zero-copy of the trace data from the write of the event
to going into a file.

trace-cmd defaults to using splice to copy the tracing ring buffer directly
into files to avoid as much copying during live recordings as possible.

Whatever changes we make, I would like to make sure there's no regressions
in performance of trace-cmd record.

Thanks,

-- Steve