Re: [PATCHv5 17/28] mm, thp: remove infrastructure for handling splitting PMDs

From: Jerome Marchand
Date: Wed Apr 29 2015 - 12:14:51 EST

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On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> With new refcounting we don't need to mark PMDs splitting. Let's drop code
> to handle this.
>
> Arch-specific code will removed separately.

This series only removed code from x86 arch. Does that mean other arches
patches will come later?

Jerome

>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> ---
> fs/proc/task_mmu.c | 8 +++----
> include/asm-generic/pgtable.h | 5 ----
> include/linux/huge_mm.h | 9 --------
> mm/gup.c | 7 ------
> mm/huge_memory.c | 54 ++++++++-----------------------------------
> mm/memcontrol.c | 14 ++---------
> mm/memory.c | 18 ++-------------
> mm/mincore.c | 2 +-
> mm/pgtable-generic.c | 14 -----------
> mm/rmap.c | 4 +---
> 10 files changed, 20 insertions(+), 115 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 95bc384ee3f7..edd63c40ed71 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -534,7 +534,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> pte_t *pte;
> spinlock_t *ptl;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> smaps_pmd_entry(pmd, addr, walk);
> spin_unlock(ptl);
> return 0;
> @@ -799,7 +799,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> spinlock_t *ptl;
> struct page *page;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
> clear_soft_dirty_pmd(vma, addr, pmd);
> goto out;
> @@ -1112,7 +1112,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> pte_t *pte, *orig_pte;
> int err = 0;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> int pmd_flags2;
>
> if ((vma->vm_flags & VM_SOFTDIRTY) || pmd_soft_dirty(*pmd))
> @@ -1416,7 +1416,7 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
> pte_t *orig_pte;
> pte_t *pte;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> pte_t huge_pte = *(pte_t *)pmd;
> struct page *page;
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 39f1d6a2b04d..fe617b7e4be6 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -184,11 +184,6 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> #endif
>
> -#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH
> -extern void pmdp_splitting_flush(struct vm_area_struct *vma,
> - unsigned long address, pmd_t *pmdp);
> -#endif
> -
> #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
> extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
> pgtable_t pgtable);
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 47f80207782f..0382230b490f 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -49,15 +49,9 @@ enum transparent_hugepage_flag {
> #endif
> };
>
> -enum page_check_address_pmd_flag {
> - PAGE_CHECK_ADDRESS_PMD_FLAG,
> - PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG,
> - PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG,
> -};
> extern pmd_t *page_check_address_pmd(struct page *page,
> struct mm_struct *mm,
> unsigned long address,
> - enum page_check_address_pmd_flag flag,
> spinlock_t **ptl);
> extern int pmd_freeable(pmd_t pmd);
>
> @@ -102,7 +96,6 @@ extern unsigned long transparent_hugepage_flags;
> #define split_huge_page(page) BUILD_BUG()
> #define split_huge_pmd(__vma, __pmd, __address) BUILD_BUG()
>
> -#define wait_split_huge_page(__anon_vma, __pmd) BUILD_BUG();
> #if HPAGE_PMD_ORDER >= MAX_ORDER
> #error "hugepages can't be allocated by the buddy allocator"
> #endif
> @@ -169,8 +162,6 @@ static inline int split_huge_page(struct page *page)
> {
> return 0;
> }
> -#define wait_split_huge_page(__anon_vma, __pmd) \
> - do { } while (0)
> #define split_huge_pmd(__vma, __pmd, __address) \
> do { } while (0)
> static inline int hugepage_madvise(struct vm_area_struct *vma,
> diff --git a/mm/gup.c b/mm/gup.c
> index 53f9681b7b30..0cebfa76fd0c 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -207,13 +207,6 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> spin_unlock(ptl);
> return follow_page_pte(vma, address, pmd, flags);
> }
> -
> - if (unlikely(pmd_trans_splitting(*pmd))) {
> - spin_unlock(ptl);
> - wait_split_huge_page(vma->anon_vma, pmd);
> - return follow_page_pte(vma, address, pmd, flags);
> - }
> -
> if (flags & FOLL_SPLIT) {
> int ret;
> page = pmd_page(*pmd);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 16c6c262385c..23181f836b62 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -889,15 +889,6 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> goto out_unlock;
> }
>
> - if (unlikely(pmd_trans_splitting(pmd))) {
> - /* split huge page running from under us */
> - spin_unlock(src_ptl);
> - spin_unlock(dst_ptl);
> - pte_free(dst_mm, pgtable);
> -
> - wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
> - goto out;
> - }
> src_page = pmd_page(pmd);
> VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
> get_page(src_page);
> @@ -1403,7 +1394,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> spinlock_t *ptl;
> int ret = 0;
>
> - if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (__pmd_trans_huge_lock(pmd, vma, &ptl)) {
> struct page *page;
> pgtable_t pgtable;
> pmd_t orig_pmd;
> @@ -1443,7 +1434,6 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> pmd_t *old_pmd, pmd_t *new_pmd)
> {
> spinlock_t *old_ptl, *new_ptl;
> - int ret = 0;
> pmd_t pmd;
>
> struct mm_struct *mm = vma->vm_mm;
> @@ -1452,7 +1442,7 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> (new_addr & ~HPAGE_PMD_MASK) ||
> old_end - old_addr < HPAGE_PMD_SIZE ||
> (new_vma->vm_flags & VM_NOHUGEPAGE))
> - goto out;
> + return 0;
>
> /*
> * The destination pmd shouldn't be established, free_pgtables()
> @@ -1460,15 +1450,14 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> */
> if (WARN_ON(!pmd_none(*new_pmd))) {
> VM_BUG_ON(pmd_trans_huge(*new_pmd));
> - goto out;
> + return 0;
> }
>
> /*
> * We don't have to worry about the ordering of src and dst
> * ptlocks because exclusive mmap_sem prevents deadlock.
> */
> - ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
> - if (ret == 1) {
> + if (__pmd_trans_huge_lock(old_pmd, vma, &old_ptl)) {
> new_ptl = pmd_lockptr(mm, new_pmd);
> if (new_ptl != old_ptl)
> spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> @@ -1484,9 +1473,9 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> if (new_ptl != old_ptl)
> spin_unlock(new_ptl);
> spin_unlock(old_ptl);
> + return 1;
> }
> -out:
> - return ret;
> + return 0;
> }
>
> /*
> @@ -1502,7 +1491,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> spinlock_t *ptl;
> int ret = 0;
>
> - if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (__pmd_trans_huge_lock(pmd, vma, &ptl)) {
> pmd_t entry;
> bool preserve_write = prot_numa && pmd_write(*pmd);
> ret = 1;
> @@ -1543,17 +1532,8 @@ int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
> spinlock_t **ptl)
> {
> *ptl = pmd_lock(vma->vm_mm, pmd);
> - if (likely(pmd_trans_huge(*pmd))) {
> - if (unlikely(pmd_trans_splitting(*pmd))) {
> - spin_unlock(*ptl);
> - wait_split_huge_page(vma->anon_vma, pmd);
> - return -1;
> - } else {
> - /* Thp mapped by 'pmd' is stable, so we can
> - * handle it as it is. */
> - return 1;
> - }
> - }
> + if (likely(pmd_trans_huge(*pmd)))
> + return 1;
> spin_unlock(*ptl);
> return 0;
> }
> @@ -1569,7 +1549,6 @@ int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
> pmd_t *page_check_address_pmd(struct page *page,
> struct mm_struct *mm,
> unsigned long address,
> - enum page_check_address_pmd_flag flag,
> spinlock_t **ptl)
> {
> pgd_t *pgd;
> @@ -1592,21 +1571,8 @@ pmd_t *page_check_address_pmd(struct page *page,
> goto unlock;
> if (pmd_page(*pmd) != page)
> goto unlock;
> - /*
> - * split_vma() may create temporary aliased mappings. There is
> - * no risk as long as all huge pmd are found and have their
> - * splitting bit set before __split_huge_page_refcount
> - * runs. Finding the same huge pmd more than once during the
> - * same rmap walk is not a problem.
> - */
> - if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
> - pmd_trans_splitting(*pmd))
> - goto unlock;
> - if (pmd_trans_huge(*pmd)) {
> - VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
> - !pmd_trans_splitting(*pmd));
> + if (pmd_trans_huge(*pmd))
> return pmd;
> - }
> unlock:
> spin_unlock(*ptl);
> return NULL;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f659d4f77138..1bc6a77067ad 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4888,7 +4888,7 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
> pte_t *pte;
> spinlock_t *ptl;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
> mc.precharge += HPAGE_PMD_NR;
> spin_unlock(ptl);
> @@ -5056,17 +5056,7 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> union mc_target target;
> struct page *page;
>
> - /*
> - * We don't take compound_lock() here but no race with splitting thp
> - * happens because:
> - * - if pmd_trans_huge_lock() returns 1, the relevant thp is not
> - * under splitting, which means there's no concurrent thp split,
> - * - if another thread runs into split_huge_page() just after we
> - * entered this if-block, the thread must wait for page table lock
> - * to be unlocked in __split_huge_page_splitting(), where the main
> - * part of thp split is not executed yet.
> - */
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> if (mc.precharge < HPAGE_PMD_NR) {
> spin_unlock(ptl);
> return 0;
> diff --git a/mm/memory.c b/mm/memory.c
> index 61e7ed722760..1bad3766b00c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -565,7 +565,6 @@ int __pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> {
> spinlock_t *ptl;
> pgtable_t new = pte_alloc_one(mm, address);
> - int wait_split_huge_page;
> if (!new)
> return -ENOMEM;
>
> @@ -585,18 +584,14 @@ int __pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
>
> ptl = pmd_lock(mm, pmd);
> - wait_split_huge_page = 0;
> if (likely(pmd_none(*pmd))) { /* Has another populated it ? */
> atomic_long_inc(&mm->nr_ptes);
> pmd_populate(mm, pmd, new);
> new = NULL;
> - } else if (unlikely(pmd_trans_splitting(*pmd)))
> - wait_split_huge_page = 1;
> + }
> spin_unlock(ptl);
> if (new)
> pte_free(mm, new);
> - if (wait_split_huge_page)
> - wait_split_huge_page(vma->anon_vma, pmd);
> return 0;
> }
>
> @@ -612,8 +607,7 @@ int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
> if (likely(pmd_none(*pmd))) { /* Has another populated it ? */
> pmd_populate_kernel(&init_mm, pmd, new);
> new = NULL;
> - } else
> - VM_BUG_ON(pmd_trans_splitting(*pmd));
> + }
> spin_unlock(&init_mm.page_table_lock);
> if (new)
> pte_free_kernel(&init_mm, new);
> @@ -3299,14 +3293,6 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> if (pmd_trans_huge(orig_pmd)) {
> unsigned int dirty = flags & FAULT_FLAG_WRITE;
>
> - /*
> - * If the pmd is splitting, return and retry the
> - * the fault. Alternative: wait until the split
> - * is done, and goto retry.
> - */
> - if (pmd_trans_splitting(orig_pmd))
> - return 0;
> -
> if (pmd_protnone(orig_pmd))
> return do_huge_pmd_numa_page(mm, vma, address,
> orig_pmd, pmd);
> diff --git a/mm/mincore.c b/mm/mincore.c
> index be25efde64a4..feb867f5fdf4 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -117,7 +117,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> unsigned char *vec = walk->private;
> int nr = (end - addr) >> PAGE_SHIFT;
>
> - if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> + if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
> memset(vec, 1, nr);
> spin_unlock(ptl);
> goto out;
> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
> index c25f94b33811..2fe699cedd4d 100644
> --- a/mm/pgtable-generic.c
> +++ b/mm/pgtable-generic.c
> @@ -133,20 +133,6 @@ pmd_t pmdp_clear_flush(struct vm_area_struct *vma, unsigned long address,
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> #endif
>
> -#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> - pmd_t *pmdp)
> -{
> - pmd_t pmd = pmd_mksplitting(*pmdp);
> - VM_BUG_ON(address & ~HPAGE_PMD_MASK);
> - set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> - /* tlb flush only to serialize against gup-fast */
> - flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
> -}
> -#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> -#endif
> -
> #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 4ca4b5cffd95..1636a96e5f71 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -737,8 +737,7 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
> * rmap might return false positives; we must filter
> * these out using page_check_address_pmd().
> */
> - pmd = page_check_address_pmd(page, mm, address,
> - PAGE_CHECK_ADDRESS_PMD_FLAG, &ptl);
> + pmd = page_check_address_pmd(page, mm, address, &ptl);
> if (!pmd)
> return SWAP_AGAIN;
>
> @@ -748,7 +747,6 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
> return SWAP_FAIL; /* To break the loop */
> }
>
> - /* go ahead even if the pmd is pmd_trans_splitting() */
> if (pmdp_clear_flush_young_notify(vma, address, pmd))
> referenced++;
>
>

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