linux-kernel - Re: [PATCH v2 2/2] relatime: Allow making relatime the default behaviour

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Date:	Thu, 27 Nov 2008 16:35:35 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	mingo@...hat.com, val.henson@...il.com, matthew@....cx
Subject: Re: [PATCH v2 2/2] relatime: Allow making relatime the default
 behaviour

> +config DEFAULT_RELATIME
> +	bool "Mount all filesystems with relatime by default"
> +	default y

NAK this

This is a change in behaviour and you don't turn it on by default so most
users will miss it. You don't need it anyway and it doesn't need to be
a kernel configuration option

> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -135,6 +135,7 @@ extern int dir_notify_enable;
>  #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
>  #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
>  #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
> +#define MS_NORELATIME	(1<<24)	/* Disable relatime even if the default */

NAK this

Putting in extra flags to allow the kernel and user space to fight each
other over mount defaults is a recipe for disaster. Take your userspace
mount command and beat it up appropriately. If you want a mount command
that defaults to relatime then ship a mount command that does.

This patch really doesn't make sense.

You add a compile time option to vary behaviour
Because it is compile time you then add a way to change it back at runtime
Because you need to override this you then add a flag to mount

It's rather easier just to fix your distribution mount package.

Also please keep different features in different patches. This patch
muddles together

- Improvements to relatime algorithms for stuff like tmpwatch
- A large chunk of material to do with changing mount behaviour

The two are I think unrelated and the algorithm change looks quite
sensible.

Alan
PS: NTL still hates you ;)
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