linux-kernel - Re: [PATCH] pipe: don't update {a,c,m}time for anonymous pipes

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Message-ID: <CAHk-=whwYt=hRk3EG7ASM-=xi3Xp7f82Ltqa=dtbVfZnGhN9ow@mail.gmail.com>
Date: Tue, 4 Feb 2025 07:28:49 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Christian Brauner <brauner@...nel.org>, David Howells <dhowells@...hat.com>, 
	"Gautham R. Shenoy" <gautham.shenoy@....com>, K Prateek Nayak <kprateek.nayak@....com>, 
	Mateusz Guzik <mjguzik@...il.com>, Neeraj Upadhyay <Neeraj.Upadhyay@....com>, 
	Oliver Sang <oliver.sang@...el.com>, Swapnil Sapkal <swapnil.sapkal@....com>, 
	WangYuli <wangyuli@...ontech.com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pipe: don't update {a,c,m}time for anonymous pipes

On Tue, 4 Feb 2025 at 05:22, Oleg Nesterov <oleg@...hat.com> wrote:
>
> @@ -404,7 +409,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
>         if (wake_next_reader)
>                 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
>         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
> -       if (ret > 0)
> +       if (ret > 0 && !is_pipe_inode(file_inode(filp)))
>                 file_accessed(filp);
>         return ret;
>  }

So I really don't kike that "is_pipe_inode()" thing.

Yes, it has superficial naming problems (it should be about
*anonymous* pipes, and that should be reflected in the name), but I
think the deeper problem is that I think this should just be a
different set of read/write functions entirely.

IOW, we should have "anon_pipe_read()" and "anon_pipe_write()", and
then the named pipes just do

    int ret = anon_pipe_read(...);
    if (ret > 0)
        file_accessed(filp);
    return ret;

instead. With no tests for "what kind of pipe is this" (same for the
write side, of course)

               Linus