Re: Should PAGE_CACHE_SIZE be discarded?

[David Howells <dhowells@redhat.com>]

Benny Halevy <bhalevy@panasas.com> wrote:

> I think that what Nick was trying to say is that PAGE_CACHE_SIZE should
> always be used properly as the size of the memory struct Page covers (while
> PAGE_SIZE is the hardware page size and the constraint is that
> PAGE_CACHE_SIZE == (PAGE_SIZE << k) for some k >= 0).  If everybody does
> that then "None of the filesystems should really care at all". That said, it
> doesn't seem like the current usage in fs/ and drivers/ is consistent with
> this convention.

Indeed.  One thing you have to consider is kmap().  I would expect it to
present an area of PAGE_SIZE for access.  However, if the filesystem gets an
area of PAGE_CACHE_SIZE to fill, then I would have to do multiple kmap() calls
in the process of filling that 'pagecache page' in AFS.

Furthermore, if a page struct covers a PAGE_CACHE_SIZE chunk of memory, then I
suspect the page allocator is also wrong, as it I believe it deals with
PAGE_SIZE chunks of memory, assuming a struct page for each.

David