On Tue, Jun 02, 2026 at 03:06:07PM -0700, Linus Torvalds wrote:

On Tue, 2 Jun 2026 at 14:37, Pedro Falcato [off-list ref] wrote:

quoted

Well, that's most definitely part of my patch. Also, you cannot outright
remove splice() functionality

That isn't what Askar's patch ever did.

You apparently didn't even read it.

 
Well, I was replying to Askar's new idea to remove pagecache-to-pipe splice,
which is what he suggested. And directly intersects with my sysctl-to-disable-splice
patch.

Honestly, I think you are the one out of line here.

Askar did something I suggested years ago, and didn't remove any functionality.

It just changes vmsplice to be a copying model (one of the directions
already was). It doesn't change regular splice at all.

And yes, it has the potential to be a visible behavior difference - if
some insane user uses vmsplice and then modifies the buffer
*afterwards*, then that would be semantically different between a
zero-copy and a normal copy.

But that would be insane behavior, and was never really reliable
anyway even with zero-copy (ie subsequent writes to user space buffers
would potentially do COW breaking based purely on timing and memory
pressure etc, so anybody who relied on it being visible wasn't goign
to get it realiably anyway)

Perhaps more importantly, it has the potential to change performance -
zero-copy *can* be a performance win, although typically it really
doesn't tend to be (looking up the page mapping is often slower than
copying).

I would expect it to be very clear in trivial benchmarks that aren't
actually real loads. And probably not visible anywhere else.

Yes, vmsplice() sucks, and we know it. Hopefully no one else will see the
difference. I don't think we can say the same for splice(), though.

Trying to make it look like Askar is the problem is only making you look worse.

To be clear, I don't think Askar is the (or a) problem. I'm glad he's
contributing, and getting rid of bad kernel interfaces is always nice. I was
just a little frustrated with a parallel splice-related-unscrew patch.

(Askar, if I was too hostile, I do sincerely apologize.)

-- 
Pedro