On 08/05/22 20:57, David Hildenbrand wrote: > On 05.08.22 20:33, Mike Kravetz wrote: > > On 08/05/22 20:25, David Hildenbrand wrote: > >> On 05.08.22 20:23, Mike Kravetz wrote: > >>> On 08/05/22 14:14, Peter Xu wrote: > >>>> On Fri, Aug 05, 2022 at 01:03:28PM +0200, David Hildenbrand wrote: > >>>>> diff --git a/mm/mmap.c b/mm/mmap.c > >>>>> index 61e6135c54ef..462a6b0344ac 100644 > >>>>> --- a/mm/mmap.c > >>>>> +++ b/mm/mmap.c > >>>>> @@ -1683,6 +1683,13 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) > >>>>> if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED))) > >>>>> return 0; > >>>>> > >>>>> + /* > >>>>> + * Hugetlb does not require/support writenotify; especially, it does not > >>>>> + * support softdirty tracking. > >>>>> + */ > >>>>> + if (is_vm_hugetlb_page(vma)) > >>>>> + return 0; > >>>> > >>>> I'm kind of confused here.. you seems to be fixing up soft-dirty for > >>>> hugetlb but here it's explicitly forbidden. > >>>> > >>>> Could you explain a bit more on why this patch is needed if (assume > >>>> there'll be a working) patch 2 being provided? > >>>> > >>> > >>> No comments on the patch, but ... > >>> > >>> Since it required little thought, I ran the test program on next-20220802 and > >>> was surprised that the issue did not recreate. Even added a simple printk > >>> to make sure we were getting into vma_wants_writenotify with a hugetlb vma. > >>> We were. > >> > >> > >> ... does your config have CONFIG_MEM_SOFT_DIRTY enabled? > >> > > > > No, Duh! > > > > FYI - Some time back, I started looking at adding soft dirty support for > > hugetlb mappings. I did not finish that work. But, I seem to recall > > places where code was operating on hugetlb mappings when perhaps it should > > not. > > > > Perhaps, it would also be good to just disable soft dirty for hugetlb at > > the source? > > I thought about that as well. But I came to the conclusion that without > patch #2, hugetlb VMAs cannot possibly support write-notify, so there is > no need to bother in vma_wants_writenotify() at all. > > The "root" would be places where we clear VM_SOFTDIRTY. That should only > be fs/proc/task_mmu.c:clear_refs_write() IIRC. > > So I don't particularly care, I consider this patch a bit cleaner and > more generic, but I can adjust clear_refs_write() instead of there is a > preference. > After a closer look, I agree that this may be the simplest/cleanest way to proceed. I was going to suggest that you note hugetlb does not support softdirty, but see you did in the comment. Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> -- Mike Kravetz
