Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race

[Hillf Danton]

On March 02, 2017 11:11 PM Kirill A. Shutemov wrote: 
> 
> Basically the same race as with numa balancing in change_huge_pmd(), but
> a bit simpler to mitigate: we don't need to preserve dirty/young flags
> here due to MADV_FREE functionality.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  mm/huge_memory.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index bb2b3646bd78..324217c31ec9 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1566,8 +1566,6 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  		deactivate_page(page);
> 
>  	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
> -		orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
> -			tlb->fullmm);
>  		orig_pmd = pmd_mkold(orig_pmd);
>  		orig_pmd = pmd_mkclean(orig_pmd);
> 
$ grep -n set_pmd_at  linux-4.10/arch/powerpc/mm/pgtable-book3s64.c

/*
 * set a new huge pmd. We should not be called for updating
 * an existing pmd entry. That should go via pmd_hugepage_update.
 */
void set_pmd_at(struct mm_struct *mm, unsigned long addr,