On Mon, Dec 02, 2013 at 02:44:34PM -0800, Andrew Morton wrote:
> On Thu, 28 Nov 2013 16:48:38 +0900 Joonsoo Kim <iamjoonsoo....@lge.com> wrote:
>
> > We have to recompute pgoff if the given page is huge, since result based
> > on HPAGE_SIZE is not approapriate for scanning the vma interval tree, as
> > shown by commit 36e4f20af833 ("hugetlb: do not use vma_hugecache_offset()
> > for vma_prio_tree_foreach") and commit 369a713e ("rmap: recompute pgoff
> > for unmapping huge page").
> >
> > ...
> >
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1714,6 +1714,10 @@ static int rmap_walk_file(struct page *page, int
> > (*rmap_one)(struct page *,
> >
> > if (!mapping)
> > return ret;
> > +
> > + if (PageHuge(page))
> > + pgoff = page->index << compound_order(page);
> > +
> > mutex_lock(&mapping->i_mmap_mutex);
> > vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> > unsigned long address = vma_address(page, vma);
>
> a) Can't we just do this?
>
> --- a/mm/rmap.c~mm-rmap-recompute-pgoff-for-huge-page-fix
> +++ a/mm/rmap.c
> @@ -1708,16 +1708,13 @@ static int rmap_walk_file(struct page *p
> struct vm_area_struct *, unsigned long, void *), void *arg)
> {
> struct address_space *mapping = page->mapping;
> - pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> + pgoff_t pgoff = page->index << compound_order(page);
> struct vm_area_struct *vma;
> int ret = SWAP_AGAIN;
>
> if (!mapping)
> return ret;
>
> - if (PageHuge(page))
> - pgoff = page->index << compound_order(page);
> -
> mutex_lock(&mapping->i_mmap_mutex);
> vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> unsigned long address = vma_address(page, vma);
>
> compound_order() does the right thing for all styles of page, yes?
Yes. I will change.
>
> b) If that PageHuge() test you added the correct thing to use?
>
> /*
> * PageHuge() only returns true for hugetlbfs pages, but not for normal or
> * transparent huge pages. See the PageTransHuge() documentation for more
> * details.
> */
>
> Obviously we won't be encountering transparent huge pages here,
> but what's the best future-safe approach?
compound_order() also works for transparent huge pages, so it may be safe way.
> I hate that PageHuge() oddity with a passion! Maybe it would be better
> if it was called PageHugetlbfs.
I also think that PageHuge() is odd name.
It has only 50 call sites. Let's change it :)
Thanks.
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