On Thu, 2012-07-12 at 13:16 +0200, Michal Hocko wrote: > On Wed 11-07-12 18:48:02, Will Deacon wrote: > > On Tue, Jul 10, 2012 at 11:42:34AM +0100, Will Deacon wrote: > > > On Tue, Jul 10, 2012 at 10:45:13AM +0100, Will Deacon wrote: > > > > On Tue, Jul 10, 2012 at 12:57:14AM +0100, Hugh Dickins wrote: > > > > > If I start to grep the architectures for non-empty flush_dcache_page(), > > > > > I soon find things in arch/arm such as v4_mc_copy_user_highpage() doing > > > > > if (!test_and_set_bit(PG_dcache_clean,)) __flush_dcache_page() - where > > > > > the naming suggests that I'm right, it's the architecture's responsibility > > > > > to arrange whatever flushing is needed in its copy and clear page functions. > > > > [...] > > > > > Ok, so this is exactly the problem. The hugetlb allocator uses its own > > > pool of huge pages, so free_huge_page followed by a later alloc_huge_page > > > will give you something where the page flags of the compound head do not > > > guarantee that PG_arch_1 is clear. > > > > Just to confirm, the following quick hack at least results in the correct > > flushing for me (on ARM): > > > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index e198831..7a7c9d3 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -1141,6 +1141,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, > > } > > > > set_page_private(page, (unsigned long)spool); > > + clear_bit(PG_arch_1, &page->flags); > > > > vma_commit_reservation(h, vma, addr); > > > > > > > > The question is whether we should tidy that up for the core code or get > > architectures to clear the bit in arch_make_huge_pte (which also seems to > > work). > > This should go into arch specific code IMO. Even the page flag name > suggests this shouldn't be in the base code. Agree completely. PG_Arch_1 is mostly used for flushing implementations, but it's meaning isn't unified. For instance Arm and Parisc have opposite meanings for this flag. Touching it in generic code can therefore *never* be the right thing to do. What you're looking for here is the correct flushing (or rather flush notification) interface. James -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>