Re: [PTCH] push down lock_super and BKL into ->put_super

[Theodore Tso <tytso@mit.edu>]

On Wed, May 06, 2009 at 07:46:22AM +0100, Al Viro wrote:
> 
> FS blocking writeback may very well be, though.
> 
> In any case, the point is that we should separate get_fs_excl() from
> exclusion there and kill exclusion part for everything except ext4.

Note that I already have patches queued for ext4 that removes the use
of lock_super() for everything other than write_super() exclusion.
(i.e., we were using it to protect oneline resize and the orphan
list.)  Similar patches are needed for ext3, which I'll backport
before the next merge window.

BTW, I'm *not* at all convinced that get_fs_excl() is the right
interface for boosting I/O priority, since it only boosts priority for
idle processes.  So high priority processes will still get screwed by
normal I/O.  Hence, in the common case, where there are no I/O class
nince processes, get_fs_excl() is a no-op anyway.  And the case which
I'm personally most interested in, which is real-time processes that
want to do I/O and so have an elevated I/O priority, get_fs_excl()
does nothing for them.

						- Ted