On Tue, May 07, 2013 at 04:45:54PM -0400, [email protected] wrote: > From: Jerome Glisse <[email protected]> > > Do not increase page count if FOLL_GET is not set. > > Signed-off-by: Jerome Glisse <[email protected]> > --- > mm/hugetlb.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 1a12f5b..5d1e46b 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -2991,7 +2991,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct > vm_area_struct *vma, > same_page: > if (pages) { > pages[i] = mem_map_offset(page, pfn_offset); > - get_page(pages[i]); > + if (flags & FOLL_GET) { > + get_page_foll(pages[i]); > + } > } > > if (vmas) > --
Hi Jerome, I think that we need to be careful in handling tail pages, because __get_page_tail_foll() uses page->_mapcount as refcount. When you get refcount on a tail page and free the hugepage without putting the *mapcount*, you will hit BUG_ON() in free_huge_page(). Yes, this is a very tricky workaround for thp, so to avoid making things too complicated, I think either of the following is better: - to get refcount only for head pages, or - to introduce a hugetlbfs variant of get_page_foll(). BTW, who do you expect is the caller of follow_hugetlb_page() with FOLL_GET (I can't find your subsequent patches 2/3 or 3/3)? I'm interested in this change because in my project it's necessary to implement this for hugepage migration (see https://lkml.org/lkml/2013/3/22/553). Thanks, Naoya Horiguchi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
