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

[Jerome Marchand <jmarchan@redhat.com>]

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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@linux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@oracle.com>
> ---
>  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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