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SubjectRe: [PATCHSET] Refactor barrier=/nobarrier flags from fs to block layer
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 the term "barrier" is obsolete having been changed into flushes in 2.6.36, and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).
> 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

Just to be clear, I strongly object to remove the mount options.

"Barrier" and "poke a control knob in the block" layer are both equally
mysterious and meaningless to real users, so I do not see this as a gain,


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