Re: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support

Christoph Hellwig
2007-06-14T21:08:13Z

On Thu, Jun 14, 2007 at 01:06:45PM -0700, Andrew Morton wrote:
> On Thu, 14 Jun 2007 12:38:39 -0700
> clameter@sgi.com wrote:
>
> > This patchset cleans up the page cache handling by replacing
> > open coded shifts and adds through inline function calls.
>
> If we never inflict variable PAGE_CACHE_SIZE upon the kernel, these changes
> become pointless obfuscation.
>
> Let's put our horses ahead of our carts. We had a lengthy discussion about
> variable PAGE_CACHE_SIZE in which I pointed out that the performance
> benefits could be replicated in a manner which doesn't add complexity to
> core VFS and which provides immediate benefit to all filesystems without
> any need to alter them: populate contiguous pagecache pages with physically
> contiguous pages.
>
> I think the best way to proceed would be to investigate that _general_
> optimisation and then, based upon the results of that work, decide whether
> further _specialised_ changes such as variable PAGE_CACHE_SIZE are needed,
> and if so, what they should be.

Christophs patches are an extremly useful cleanup and can stand on their
own. Right now PAGE_CACHE_SIZE and friends are in there and now one can
keep them distinct because their useage is not clear at all. By making
the macros per-mapping at least the useage is clear.

That beeing said we should do a full conversion so that PAGE_CACHE_SIZE
just goes away, otherwise the whole excercise is rather pointless.