Re: [PATCH] rmap: fix pgoff calculation to handle hugepage correctly

Kirill A. Shutemov
2014-07-01T20:16:03Z

On Tue, Jul 01, 2014 at 02:50:21PM -0400, Naoya Horiguchi wrote:
> On Tue, Jul 01, 2014 at 09:07:39PM +0300, Kirill A. Shutemov wrote:
> > Why do we need this special case for hugetlb page ->index? Why not use
> > PAGE_SIZE units there too? Or I miss something?
>
> hugetlb pages are never split, so we use larger page cache size for
> hugetlbfs file (to avoid large sparse page cache tree.)

For transparent huge page cache I would like to have native support in
page cache radix-tree: since huge pages are always naturally aligned we
can create a leaf node for it several (RADIX_TREE_MAP_SHIFT -
HPAGE_PMD_ORDER) levels up by tree, which would cover all indexes in the
range the huge page represents. This approach should fit hugetlb too. And
-1 special case for hugetlb.
But I'm not sure when I'll get time to play with this...

--
Kirill A. Shutemov