Re: [PATCHSET] Refactor barrier=/nobarrier flags from fs to block layer

[Ric Wheeler <rwheeler@redhat.com>]

On 01/26/2011 02:12 AM, Darrick J. Wong wrote:
> Hello,
>
>  From what I can tell, most of the filesystems that know how to issue commands
> to flush the write cache also have some mechanism for the user to override
> whether or not the filesystem actually issues those flushes.  Unfortunately,
> the term "barrier" is obsolete having been changed into flushes in 2.6.36, and
> many of the filesystems implement the mount options with slightly different
> syntaxes (barrier=[0|1|none|flush], nobarrier, etc).

Why remove the mount option? We have been using that term and educating users 
about how to use it for many, many years.

I see no reason to remove mount options at all.

Ric

> This patchset adds to the block layer a sysfs knob that an administrator can
> use to disable flushes, and removes the mount options from the filesystem code.
> As a starting point, I'm removing the mount options and flush toggle from
> jbd2/ext4.
>
> Anyway, I'm looking for some feedback about refactoring the barrier/flush
> control knob into the block layer.  It sounds like we want a knob that picks
> the safest option (issue flushes when supported) unless the administrator
> decides that it is appropriate to do otherwise.  I suspect that there are good
> arguments for not having a knob at all, and good arguments for a safe knob.
> However, since I don't see the barrier options being removed en masse, I'm
> assuming that we still want a knob somewhere.  Do we need the ignore_fua knob
> too?  Is this the proper way to deprecate mount options out of filesystems?
>
> --D