Re: [PATCH 02/31] mm/migrate: remove cruft from migration_entry_wait()s
From: Alistair Popple
Date: Mon May 22 2023 - 21:47:33 EST
Hugh Dickins <hughd@xxxxxxxxxx> writes:
> migration_entry_wait_on_locked() does not need to take a mapped pte
> pointer, its callers can do the unmap first. Annotate it with
> __releases(ptl) to reduce sparse warnings.
Thanks Hugh, I debated doing something similar when I reworked this to
not take a pageref. However I was unsure if the pte unmap/unlock
ordering mattered as this reverses the order of operations (from unlock
then unmap to unmap then unlock).
I never found any reason why that would be a problem though so please
add:
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
> Fold __migration_entry_wait_huge() into migration_entry_wait_huge().
> Fold __migration_entry_wait() into migration_entry_wait(), preferring
> the tighter pte_offset_map_lock() to pte_offset_map() and pte_lockptr().
>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
> include/linux/migrate.h | 4 ++--
> include/linux/swapops.h | 17 +++--------------
> mm/filemap.c | 13 ++++---------
> mm/migrate.c | 37 +++++++++++++------------------------
> 4 files changed, 22 insertions(+), 49 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 6241a1596a75..affea3063473 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -75,8 +75,8 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode);
>
> int migrate_huge_page_move_mapping(struct address_space *mapping,
> struct folio *dst, struct folio *src);
> -void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
> - spinlock_t *ptl);
> +void migration_entry_wait_on_locked(swp_entry_t entry, spinlock_t *ptl)
> + __releases(ptl);
> void folio_migrate_flags(struct folio *newfolio, struct folio *folio);
> void folio_migrate_copy(struct folio *newfolio, struct folio *folio);
> int folio_migrate_mapping(struct address_space *mapping,
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 3a451b7afcb3..4c932cb45e0b 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -332,15 +332,9 @@ static inline bool is_migration_entry_dirty(swp_entry_t entry)
> return false;
> }
>
> -extern void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> - spinlock_t *ptl);
> extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> unsigned long address);
> -#ifdef CONFIG_HUGETLB_PAGE
> -extern void __migration_entry_wait_huge(struct vm_area_struct *vma,
> - pte_t *ptep, spinlock_t *ptl);
> extern void migration_entry_wait_huge(struct vm_area_struct *vma, pte_t *pte);
> -#endif /* CONFIG_HUGETLB_PAGE */
> #else /* CONFIG_MIGRATION */
> static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
> {
> @@ -362,15 +356,10 @@ static inline int is_migration_entry(swp_entry_t swp)
> return 0;
> }
>
> -static inline void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> - spinlock_t *ptl) { }
> static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> - unsigned long address) { }
> -#ifdef CONFIG_HUGETLB_PAGE
> -static inline void __migration_entry_wait_huge(struct vm_area_struct *vma,
> - pte_t *ptep, spinlock_t *ptl) { }
> -static inline void migration_entry_wait_huge(struct vm_area_struct *vma, pte_t *pte) { }
> -#endif /* CONFIG_HUGETLB_PAGE */
> + unsigned long address) { }
> +static inline void migration_entry_wait_huge(struct vm_area_struct *vma,
> + pte_t *pte) { }
> static inline int is_writable_migration_entry(swp_entry_t entry)
> {
> return 0;
> diff --git a/mm/filemap.c b/mm/filemap.c
> index b4c9bd368b7e..28b42ee848a4 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1359,8 +1359,6 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
> /**
> * migration_entry_wait_on_locked - Wait for a migration entry to be removed
> * @entry: migration swap entry.
> - * @ptep: mapped pte pointer. Will return with the ptep unmapped. Only required
> - * for pte entries, pass NULL for pmd entries.
> * @ptl: already locked ptl. This function will drop the lock.
> *
> * Wait for a migration entry referencing the given page to be removed. This is
> @@ -1369,13 +1367,13 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
> * should be called while holding the ptl for the migration entry referencing
> * the page.
> *
> - * Returns after unmapping and unlocking the pte/ptl with pte_unmap_unlock().
> + * Returns after unlocking the ptl.
> *
> * This follows the same logic as folio_wait_bit_common() so see the comments
> * there.
> */
> -void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
> - spinlock_t *ptl)
> +void migration_entry_wait_on_locked(swp_entry_t entry, spinlock_t *ptl)
> + __releases(ptl)
> {
> struct wait_page_queue wait_page;
> wait_queue_entry_t *wait = &wait_page.wait;
> @@ -1409,10 +1407,7 @@ void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
> * a valid reference to the page, and it must take the ptl to remove the
> * migration entry. So the page is valid until the ptl is dropped.
> */
> - if (ptep)
> - pte_unmap_unlock(ptep, ptl);
> - else
> - spin_unlock(ptl);
> + spin_unlock(ptl);
>
> for (;;) {
> unsigned int flags;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 01cac26a3127..3ecb7a40075f 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -296,14 +296,18 @@ void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked)
> * get to the page and wait until migration is finished.
> * When we return from this function the fault will be retried.
> */
> -void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> - spinlock_t *ptl)
> +void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> + unsigned long address)
> {
> + spinlock_t *ptl;
> + pte_t *ptep;
> pte_t pte;
> swp_entry_t entry;
>
> - spin_lock(ptl);
> + ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> pte = *ptep;
> + pte_unmap(ptep);
> +
> if (!is_swap_pte(pte))
> goto out;
>
> @@ -311,18 +315,10 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> if (!is_migration_entry(entry))
> goto out;
>
> - migration_entry_wait_on_locked(entry, ptep, ptl);
> + migration_entry_wait_on_locked(entry, ptl);
> return;
> out:
> - pte_unmap_unlock(ptep, ptl);
> -}
> -
> -void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> - unsigned long address)
> -{
> - spinlock_t *ptl = pte_lockptr(mm, pmd);
> - pte_t *ptep = pte_offset_map(pmd, address);
> - __migration_entry_wait(mm, ptep, ptl);
> + spin_unlock(ptl);
> }
>
> #ifdef CONFIG_HUGETLB_PAGE
> @@ -332,9 +328,9 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> *
> * This function will release the vma lock before returning.
> */
> -void __migration_entry_wait_huge(struct vm_area_struct *vma,
> - pte_t *ptep, spinlock_t *ptl)
> +void migration_entry_wait_huge(struct vm_area_struct *vma, pte_t *ptep)
> {
> + spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), vma->vm_mm, ptep);
> pte_t pte;
>
> hugetlb_vma_assert_locked(vma);
> @@ -352,16 +348,9 @@ void __migration_entry_wait_huge(struct vm_area_struct *vma,
> * lock release in migration_entry_wait_on_locked().
> */
> hugetlb_vma_unlock_read(vma);
> - migration_entry_wait_on_locked(pte_to_swp_entry(pte), NULL, ptl);
> + migration_entry_wait_on_locked(pte_to_swp_entry(pte), ptl);
> }
> }
> -
> -void migration_entry_wait_huge(struct vm_area_struct *vma, pte_t *pte)
> -{
> - spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), vma->vm_mm, pte);
> -
> - __migration_entry_wait_huge(vma, pte, ptl);
> -}
> #endif
>
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> @@ -372,7 +361,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
> ptl = pmd_lock(mm, pmd);
> if (!is_pmd_migration_entry(*pmd))
> goto unlock;
> - migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl);
> + migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), ptl);
> return;
> unlock:
> spin_unlock(ptl);