On Wed, Nov 14, 2007 at 03:57:46PM +0000, David Howells wrote:
> Nick Piggin <npiggin@xxxxxxx> wrote:
>
> > In core code, the PAGE_CACHE_SIZE is for page cache struct pages. Single
> > struct pages (not page arrays). Take a look at generic mapping read or
> > something.
>
> So you're saying a struct page controls an area of PAGE_CACHE_SIZE, not an
> area of PAGE_SIZE?
No, a pagecache page is PAGE_CACHE_SIZE. And not all struct pages control
the same amount of data anyway, with compound pages.
> Is a struct page then a purely pagecache concept?
>
> > Documentation is the opposite of convention ;)
>
> If it's not Documented, then it's irrelevant.
But you can't just decide yourself that it is irrelevant because you don't
grep hard enough ;)
include/linux/mm.h:
* A page may belong to an inode's memory mapping. In this case, page->mapping
* is the pointer to the inode, and page->index is the file offset of the page,
* in units of PAGE_CACHE_SIZE.
include/linux/mm_types.h
unsigned long vm_pgoff; /* Offset (within vm_file) in PAGE_SIZE
units, *not* PAGE_CACHE_SIZE */
Looks like documentation to me.
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