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

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Message-ID: <CAHk-=whetxWT58ACKO3aGPZQAb_CCpono6U_siynPuvDs2J6rg@mail.gmail.com>
Date: Tue, 4 Feb 2025 08:49:57 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Christian Brauner <brauner@...nel.org>
Cc: Mateusz Guzik <mjguzik@...il.com>, Oleg Nesterov <oleg@...hat.com>, 
	David Howells <dhowells@...hat.com>, "Gautham R. Shenoy" <gautham.shenoy@....com>, 
	K Prateek Nayak <kprateek.nayak@....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 08:34, Christian Brauner <brauner@...nel.org> wrote:
>
> So really that mnt_get_write_access() should be pointless for
> anonymous pipes. In other words, couldn't this also just be:

I bet you'll find that even just inode_update_times() isn't all that cheap.

Yes, the silly "get writability" thing is pointless for pipes, but the
"get current time" really isn't a no-op either. There's all the crazy
"coarse time vs fine time" crud, there's justv a *lot* of overhead.

That's not really noticeable on a "real" file where you never access
just one byte anyway, and where any write costs are elsewhere. But
pipes can be very cheap, so the silly overheads really show up.

                 Linus