linux-kernel - Re: [PATCH 03/10] thp: Prepare for DAX huge pages

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Date:	Sun, 19 Jul 2015 14:03:05 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 03/10] thp: Prepare for DAX huge pages

On Fri, Jul 10, 2015 at 04:29:18PM -0400, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@...ux.intel.com>
> 
> Add a vma_is_dax() helper macro to test whether the VMA is DAX, and use
> it in zap_huge_pmd() and __split_huge_page_pmd().
> 
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> ---
>  include/linux/dax.h |  4 ++++
>  mm/huge_memory.c    | 46 ++++++++++++++++++++++++++++------------------
>  2 files changed, 32 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 4f27d3d..9b51f9d 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -18,4 +18,8 @@ int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
>  #define dax_mkwrite(vma, vmf, gb, iod)		dax_fault(vma, vmf, gb, iod)
>  #define __dax_mkwrite(vma, vmf, gb, iod)	__dax_fault(vma, vmf, gb, iod)
>  
> +static inline bool vma_is_dax(struct vm_area_struct *vma)
> +{
> +	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
> +}
>  #endif
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 911071b..b7bd855 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -23,6 +23,7 @@
>  #include <linux/pagemap.h>
>  #include <linux/migrate.h>
>  #include <linux/hashtable.h>
> +#include <linux/dax.h>
>  
>  #include <asm/tlb.h>
>  #include <asm/pgalloc.h>
> @@ -1391,7 +1392,6 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  	int ret = 0;
>  
>  	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> -		struct page *page;
>  		pgtable_t pgtable;
>  		pmd_t orig_pmd;
>  		/*
> @@ -1403,13 +1403,22 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  		orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
>  							tlb->fullmm);
>  		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> -		pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
> +		if (vma_is_dax(vma)) {
> +			if (is_huge_zero_pmd(orig_pmd)) {
> +				pgtable = NULL;

pgtable_t is not always a pointer. See arch/arc.

> +			} else {
> +				spin_unlock(ptl);
> +				return 1;
> +			}
> +		} else {
> +			pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
> +		}
>  		if (is_huge_zero_pmd(orig_pmd)) {
>  			atomic_long_dec(&tlb->mm->nr_ptes);
>  			spin_unlock(ptl);
>  			put_huge_zero_page();
>  		} else {
> -			page = pmd_page(orig_pmd);
> +			struct page *page = pmd_page(orig_pmd);
>  			page_remove_rmap(page);
>  			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
>  			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
> @@ -1418,7 +1427,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  			spin_unlock(ptl);
>  			tlb_remove_page(tlb, page);
>  		}
> -		pte_free(tlb->mm, pgtable);
> +		if (pgtable)
> +			pte_free(tlb->mm, pgtable);

It's better to drop "pgtable = NULL;" above and use "if (vma_is_dax(vma))"
here.

>  		ret = 1;
>  	}
>  	return ret;
> @@ -2887,7 +2897,7 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
>  		pmd_t *pmd)
>  {
>  	spinlock_t *ptl;
> -	struct page *page;
> +	struct page *page = NULL;
>  	struct mm_struct *mm = vma->vm_mm;
>  	unsigned long haddr = address & HPAGE_PMD_MASK;
>  	unsigned long mmun_start;	/* For mmu_notifiers */
> @@ -2900,25 +2910,25 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
>  again:
>  	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
>  	ptl = pmd_lock(mm, pmd);
> -	if (unlikely(!pmd_trans_huge(*pmd))) {
> -		spin_unlock(ptl);
> -		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
> -		return;
> -	}
> -	if (is_huge_zero_pmd(*pmd)) {
> +	if (unlikely(!pmd_trans_huge(*pmd)))
> +		goto unlock;
> +	if (vma_is_dax(vma)) {
> +		pmdp_huge_clear_flush(vma, haddr, pmd);

pmdp_huge_clear_flush_notify()

> +	} else if (is_huge_zero_pmd(*pmd)) {
>  		__split_huge_zero_page_pmd(vma, haddr, pmd);
> -		spin_unlock(ptl);
> -		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
> -		return;
> +	} else {
> +		page = pmd_page(*pmd);
> +		VM_BUG_ON_PAGE(!page_count(page), page);
> +		get_page(page);
>  	}
> -	page = pmd_page(*pmd);
> -	VM_BUG_ON_PAGE(!page_count(page), page);
> -	get_page(page);
> + unlock:
>  	spin_unlock(ptl);
>  	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
>  
> -	split_huge_page(page);
> +	if (!page)
> +		return;
>  
> +	split_huge_page(page);
>  	put_page(page);
>  
>  	/*
> -- 
> 2.1.4
> 
> --
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-- 
 Kirill A. Shutemov
--
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