Re: [PATCH 86/87] fs: switch timespec64 fields in inode to discrete integers

From: Jeff Layton <jlayton@kernel.org>
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Subject: Re: [PATCH 86/87] fs: switch timespec64 fields in inode to discrete integers
Date: Thu, 28 Sep 2023 13:06:03 -0400	[thread overview]
Message-ID: <af047e4a1c6947c59d4a13d4ae221c784a5386b4.camel@kernel.org> (raw)
In-Reply-To: <6020d6e7-b187-4abb-bf38-dc09d8bd0f6d@app.fastmail.com>

On Thu, 2023-09-28 at 11:48 -0400, Arnd Bergmann wrote:
> On Thu, Sep 28, 2023, at 07:05, Jeff Layton wrote:
> > This shaves 8 bytes off struct inode, according to pahole.
> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> 
> FWIW, this is similar to the approach that Deepa suggested
> back in 2016:
> 
> https://lore.kernel.org/lkml/1452144972-15802-3-git-send-email-deepa.kernel@gmail.com/
> 
> It was NaKed at the time because of the added complexity,
> though it would have been much easier to do it then,
> as we had to touch all the timespec references anyway.
> 
> The approach still seems ok to me, but I'm not sure it's worth
> doing it now if we didn't do it then.
> 

I remember seeing those patches go by. I don't remember that change
being NaK'ed, but I wasn't paying close attention at the time 

Looking at it objectively now, I think it's worth it to recover 8 bytes
per inode and open a 4 byte hole that Amir can use to grow the
i_fsnotify_mask. We might even able to shave off another 12 bytes
eventually if we can move to a single 64-bit word per timestamp. 

It is a lot of churn though.
-- 
Jeff Layton <jlayton@kernel.org>