On Thu, Oct 10, 2013 at 06:12:41PM +0200, Andrea Arcangeli wrote: > 11feeb498086a3a5907b8148bdf1786a9b18fc55 introduced a memory leak when > KVM is run on gigantic compound pages. > > 11feeb498086a3a5907b8148bdf1786a9b18fc55 depends on the assumption > that PG_reserved is identical for all head and tail pages of a > compound page. So that if get_user_pages returns a tail page, we don't > need to check the head page in order to know if we deal with a > reserved page that requires different refcounting. > > The assumption that PG_reserved is the same for head and tail pages is > certainly correct for THP and regular hugepages, but gigantic > hugepages allocated through bootmem don't clear the PG_reserved on the > tail pages (the clearing of PG_reserved is done later only if the > gigantic hugepage is freed). > > This patch corrects the gigantic compound page initialization so that > we can retain the optimization in > 11feeb498086a3a5907b8148bdf1786a9b18fc55. The cacheline was already > modified in order to set PG_tail so this won't affect the boot time of > large memory systems. > > Reported-by: andy123 <ajs124.ajs...@gmail.com> > Signed-off-by: Andrea Arcangeli <aarca...@redhat.com> > ---
Acked-by: Rafael Aquini <aqu...@redhat.com> > mm/hugetlb.c | 18 +++++++++++++++++- > 1 file changed, 17 insertions(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index b49579c..315450e 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -695,8 +695,24 @@ static void prep_compound_gigantic_page(struct page > *page, unsigned long order) > /* we rely on prep_new_huge_page to set the destructor */ > set_compound_order(page, order); > __SetPageHead(page); > + __ClearPageReserved(page); > for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) { > __SetPageTail(p); > + /* > + * For gigantic hugepages allocated through bootmem at > + * boot, it's safer to be consistent with the > + * not-gigantic hugepages and to clear the PG_reserved > + * bit from all tail pages too. Otherwse drivers using > + * get_user_pages() to access tail pages, may get the > + * reference counting wrong if they see the > + * PG_reserved bitflag set on a tail page (despite the > + * head page didn't have PG_reserved set). Enforcing > + * this consistency between head and tail pages, > + * allows drivers to optimize away a check on the head > + * page when they need know if put_page is needed after > + * get_user_pages() or not. > + */ > + __ClearPageReserved(p); > set_page_count(p, 0); > p->first_page = page; > } > @@ -1329,9 +1345,9 @@ static void __init gather_bootmem_prealloc(void) > #else > page = virt_to_page(m); > #endif > - __ClearPageReserved(page); > WARN_ON(page_count(page) != 1); > prep_compound_huge_page(page, h->order); > + WARN_ON(PageReserved(page)); > prep_new_huge_page(h, page, page_to_nid(page)); > /* > * If we had gigantic hugepages allocated at boot time, we need > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"d...@kvack.org"> em...@kvack.org </a> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html