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. -- Thanks, David / dhildenb
