Re: Should PAGE_CACHE_SIZE be discarded?

[Nick Piggin <npiggin@suse.de>]

On Wed, Nov 14, 2007 at 03:59:39PM +0000, David Howells wrote:
> Nick Piggin <npiggin@suse.de> wrote:
> 
> > Christoph Lameter has patches exactly to make PAGE_CACHE_SIZE larger than
> > PAGE_SIZE, and they seem to work without much effort. I happen to hate the
> > patches ;) but that doesn't change the fact that PAGE_CACHE_SIZE is
> > relatively useful and it is not at all an ill-defined concept.
> 
> Where, please? mm kernels?

Floating around. I'm not saying it will even get upstream. It's just
an example.

 
> > Basically, anything that goes in the page cache is in units of
> > PAGE_CACHE_SIZE, and nothing else. For filesystems it should be pretty
> > easy...
> 
> That depends on what the coverage of struct page is.  I don't actually know
> whether this is PAGE_SIZE or PAGE_CACHE_SIZE; I assumed it to be the former,
> but from what you've said, I'm not actually sure.

It can be pretty well any power of 2 from PAGE_SIZE upwards, with
compound pages. None of the filesystems should really care at all.
It's not even a new concept, hugetlbfs uses HPAGE_SIZE...