On Thu, 10 Jun 2021, Aneesh Kumar K.V wrote:
> With TRANSPARENT_HUGEPAGE_PUD enabled the kernel can find huge PUD entries.
> Add a helper to move huge PUD entries on mremap().
>
> This will be used by a later patch to optimize mremap of PUD_SIZE aligned
> level 4 PTE mapped address
>
> This also make sure we support mremap on huge PUD entries even with
> CONFIG_HAVE_MOVE_PUD disabled.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> ---
> mm/mremap.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 73 insertions(+), 7 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 47c255b60150..92ab7d24a587 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -324,10 +324,62 @@ static inline bool move_normal_pud(struct vm_area_struct *vma,
> }
> #endif
>
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PUD
Should that say
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
?
(I'm a PUD-THP-sceptic, but if it's just for DAX then probably okay.)
> +static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
> + unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
> +{
> + spinlock_t *old_ptl, *new_ptl;
> + struct mm_struct *mm = vma->vm_mm;
> + pud_t pud;
> +
> + /*
> + * The destination pud shouldn't be established, free_pgtables()
> + * should have released it.
> + */
> + if (WARN_ON_ONCE(!pud_none(*new_pud)))
> + return false;
> +
> + /*
> + * We don't have to worry about the ordering of src and dst
> + * ptlocks because exclusive mmap_lock prevents deadlock.
> + */
> + old_ptl = pud_lock(vma->vm_mm, old_pud);
> + new_ptl = pud_lockptr(mm, new_pud);
> + if (new_ptl != old_ptl)
> + spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> +
> + /* Clear the pud */
> + pud = *old_pud;
> + pud_clear(old_pud);
> +
> + VM_BUG_ON(!pud_none(*new_pud));
> +
> + /* Set the new pud */
> + /* mark soft_ditry when we add pud level soft dirty support */
> + set_pud_at(mm, new_addr, new_pud, pud);
> + flush_pud_tlb_range(vma, old_addr, old_addr + HPAGE_PUD_SIZE);
> + if (new_ptl != old_ptl)
> + spin_unlock(new_ptl);
> + spin_unlock(old_ptl);
> +
> + return true;
> +}
> +#else
> +static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
> + unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
> +{
> + WARN_ON_ONCE(1);
> + return false;
> +
> +}
> +#endif
> +
> enum pgt_entry {
> NORMAL_PMD,
> HPAGE_PMD,
> NORMAL_PUD,
> + HPAGE_PUD,
> };
>
> /*
> @@ -347,6 +399,7 @@ static __always_inline unsigned long get_extent(enum pgt_entry entry,
> mask = PMD_MASK;
> size = PMD_SIZE;
> break;
> + case HPAGE_PUD:
> case NORMAL_PUD:
> mask = PUD_MASK;
> size = PUD_SIZE;
> @@ -395,6 +448,11 @@ static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma,
> move_huge_pmd(vma, old_addr, new_addr, old_entry,
> new_entry);
> break;
> + case HPAGE_PUD:
> + moved = move_huge_pud(vma, old_addr, new_addr, old_entry,
> + new_entry);
> + break;
> +
> default:
> WARN_ON_ONCE(1);
> break;
> @@ -414,6 +472,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
> unsigned long extent, old_end;
> struct mmu_notifier_range range;
> pmd_t *old_pmd, *new_pmd;
> + pud_t *old_pud, *new_pud;
>
> old_end = old_addr + len;
> flush_cache_range(vma, old_addr, old_end);
> @@ -429,15 +488,22 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
> * PUD level if possible.
> */
> extent = get_extent(NORMAL_PUD, old_addr, old_end, new_addr);
> - if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {
> - pud_t *old_pud, *new_pud;
>
> - old_pud = get_old_pud(vma->vm_mm, old_addr);
> - if (!old_pud)
> + old_pud = get_old_pud(vma->vm_mm, old_addr);
> + if (!old_pud)
> + continue;
> + new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
> + if (!new_pud)
> + break;
> + if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) {
> + if (extent == HPAGE_PUD_SIZE) {
> + move_pgt_entry(HPAGE_PUD, vma, old_addr, new_addr,
> + old_pud, new_pud, need_rmap_locks);
> + /* We ignore and continue on error? */
> continue;
> - new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
> - if (!new_pud)
> - break;
> + }
> + } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {
> +
> if (move_pgt_entry(NORMAL_PUD, vma, old_addr, new_addr,
> old_pud, new_pud, need_rmap_locks))
> continue;
> --
> 2.31.1
>
>
>
