linux-kernel - Re: [PATCH] fs: load the ->i_sb pointer once in inode_sb_list

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Message-ID: <Z9rtXtqFAg7S5A1k@casper.infradead.org>
Date: Wed, 19 Mar 2025 16:14:22 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Jan Kara <jack@...e.cz>
Cc: Mateusz Guzik <mjguzik@...il.com>, brauner@...nel.org,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: load the ->i_sb pointer once in
 inode_sb_list_{add,del}

On Wed, Mar 19, 2025 at 05:11:25PM +0100, Jan Kara wrote:
> On Wed 19-03-25 01:46:35, Mateusz Guzik wrote:
> > While this may sound like a pedantic clean up, it does in fact impact
> > code generation -- the patched add routine is slightly smaller.
> > 
> > Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
> 
> I'm surprised it matters for the compiler but as Christian wrote, why not.
> Feel free to add:

I suspect it's because there's a spin_lock() involved.  The barriers
we have probably mean we've told the compiler that it can't cache the
value loaded before the spin_lock().