Re: [patch 13/44] mm: restore KERNEL_DS optimisations

[Nick Piggin <npiggin@suse.de>]

On Tue, Apr 24, 2007 at 11:43:18AM +0100, Christoph Hellwig wrote:
> On Tue, Apr 24, 2007 at 11:23:59AM +1000, Nick Piggin wrote:
> > Restore the KERNEL_DS optimisation, especially helpful to the 2copy write
> > path.
> > 
> > This may be a pretty questionable gain in most cases, especially after the
> > legacy 2copy write path is removed, but it doesn't cost much.
> 
> Well, it gets removed later and sets a bad precedence.  Instead of
> adding hacks we should have proper methods for kernel-space read/writes.
> Especially as the latter are a lot simpler and most of the magic
> in this patch series is not needed.  I'll start this work once
> your patch series is in.

It was removed earlier and put back in here. I agree it isn't so
important, but again it does help that the patchset introduces no
obvious regression. You could remove it in your patchset?


> In general there seems to be a lot of stuff in the earlier patches
> that just goes away later and doesn't make much sense in the series.
> Is there a good reason not to simply consolidate out those changes
> completely?

I guess the first half of the patchset -- the slow deadlock fix for
the old prepare_write path -- came about because that's the only
reasonable way I could find to fix it. I initially thought it would
take a lot longer to convert all filesystems and that we might want
to stay compatible for a while, which is why I wanted to ensure that
was working.

Basically I can't really see which ones you think I should merge and
be able retain a working kernel?

Granted there are a couple of bugfixes and some slightly orthogonal
cleanups in there, but I just thought I'd submit them in the same
series because it was a little easier for me.