linux-kernel - Re: [PATCH 01/10] fs: turn inode ctime fields into a single ktime

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Message-ID: <ZoThH9fWsdzq7IXR@infradead.org>
Date: Tue, 2 Jul 2024 22:26:55 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jeff Layton <jlayton@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Chandan Babu R <chandan.babu@...cle.com>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, kernel-team@...com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-mm@...ck.org, linux-nfs@...r.kernel.org
Subject: Re: [PATCH 01/10] fs: turn inode ctime fields into a single ktime_t

On Tue, Jul 02, 2024 at 11:58:02AM -0400, Jeff Layton wrote:
> Yeah, mostly. We shrink struct inode by 8 bytes with that patch, and we
> (probably) get a better cache footprint, since i_version ends up in the
> same cacheline as the ctime. That's really a separate issue though, so
> I'm not too worked up about dropping that patch.
> 
> As a bonus, leaving it split across separate fields means that we can
> use unused bits in the nsec field for the flag, so we don't need to
> sacrifice any timestamp granularity either.
> 
> I've got a draft rework that does this that I'm testing now. Assuming
> it works OK, I'll resend in a few days.

So while shrinking the inodes sounds nice, the tradeoff to have to
check all timestamps from disk / the server for validity doesn't
sound as positive.  So I'm glade we're avoiding this at least for.