Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full

[K Prateek Nayak]

Hello Linus,

On 3/4/2025 2:16 AM, Linus Torvalds wrote:
> On Mon, 3 Mar 2025 at 10:28, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > Stupid question... but do we really need to change the code which update
> > tail/head if we pack them into a single word?
>
> No. It's only the READ_ONCE() parts that need changing.
>
> See this suggested patch, which does something very similar to what
> you were thinking of.
>
> ENTIRELY UNTESTED, but it seems to generate ok code. It might even
> generate better code than what we have now.

With the patch on top of commit aaec5a95d596 ("pipe_read: don't wake up
the writer if the pipe is still full"), we've not seen any hangs yet
with a few thousand iterations of short loops, and a few hundred
iterations of larger loop sizes with hackbench.

If you can provide you S-o-b, we can send out an official patch with a
commit log. We'll wait for Oleg's response in case he has any concerns.

>                 Linus

--
Thanks and Regards,
Prateek