linux-kernel - Re: [PATCH] fs: Make file-nr output the total allocated file handles

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Message-ID: <p6rnvi5kvu7zwk6ypui2gwezvg3onqeqajwtw6uksv4jagannh@q2mx54icpmig>
Date: Fri, 11 Apr 2025 23:15:12 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Christian Brauner <brauner@...nel.org>
Cc: lirongqing <lirongqing@...du.com>, viro@...iv.linux.org.uk, 
	jack@...e.cz, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Make file-nr output the total allocated file handles

On Fri, Apr 11, 2025 at 04:16:08PM +0200, Christian Brauner wrote:
> On Thu, Apr 10, 2025 at 07:21:17PM +0800, lirongqing wrote:
> > From: Li RongQing <lirongqing@...du.com>
> > 
> > Make file-nr output the total allocated file handles, not per-cpu
> > cache number, it's more precise, and not in hot path
> > 
> > Signed-off-by: Li RongQing <lirongqing@...du.com>
> > ---
> 
> That means grabbing a lock suddenly. Is there an actual use-case
> behind this?
> 

The centralized value can be really grossly inaccurate as CPU count increases.

There is some talks about fixing that, see:
https://lore.kernel.org/linux-mm/20250410175149.1206995-1-mathieu.desnoyers@efficios.com/

In the meantime, given that this is only accessed when reading the /proc
file, this should be fine?

Note it still wont delay bumps/decs as long as they fit the batch (which
is the common case).