Re: [RFC v3 PATCH 04/10] mm/hugetlb: expose hugetlb fault mutex for use by fallocate

[Naoya Horiguchi]

On Thu, May 21, 2015 at 08:47:38AM -0700, Mike Kravetz wrote:
> hugetlb page faults are currently synchronized by the table of
> mutexes (htlb_fault_mutex_table).  fallocate code will need to
> synchronize with the page fault code when it allocates or
> deletes pages.  Expose interfaces so that fallocate operations
> can be synchronized with page faults.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
>  include/linux/hugetlb.h |  3 +++
>  mm/hugetlb.c            | 23 ++++++++++++++++++++++-
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index fd337f2..d0d033e 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -82,6 +82,9 @@ void putback_active_hugepage(struct page *page);
>  bool is_hugepage_active(struct page *page);
>  void free_huge_page(struct page *page);
>  void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve);
> +u32 hugetlb_fault_mutex_shared_hash(struct address_space *mapping, pgoff_t idx);
> +void hugetlb_fault_mutex_lock(u32 hash);
> +void hugetlb_fault_mutex_unlock(u32 hash);
>  
>  #ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
>  pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud);
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 620cc9e..df0d32a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3183,7 +3183,8 @@ static u32 fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
>  	unsigned long key[2];
>  	u32 hash;
>  
> -	if (vma->vm_flags & VM_SHARED) {
> +	/* !vma implies this was called from hugetlbfs fallocate code */
> +	if (!vma || vma->vm_flags & VM_SHARED) {
>  		key[0] = (unsigned long) mapping;
>  		key[1] = idx;
>  	} else {
> @@ -3209,6 +3210,26 @@ static u32 fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
>  }
>  #endif
>  
> +/*
> + * Interfaces to the fault mutex routines for use by hugetlbfs
> + * fallocate code.  Faults must be synchronized with page adds or
> + * deletes by fallocate.  fallocate only deals with shared mappings.
> + */
> +u32 hugetlb_fault_mutex_shared_hash(struct address_space *mapping, pgoff_t idx)
> +{
> +	return fault_mutex_hash(NULL, NULL, NULL, mapping, idx, 0);
> +}
> +
> +void hugetlb_fault_mutex_lock(u32 hash)
> +{
> +	mutex_lock(&htlb_fault_mutex_table[hash]);
> +}
> +
> +void hugetlb_fault_mutex_unlock(u32 hash)
> +{
> +	mutex_unlock(&htlb_fault_mutex_table[hash]);
> +}
> +
>  int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  			unsigned long address, unsigned int flags)
>  {

You introduce new lock/unlock interfaces, so how about making the existing
user of this lock (i.e. hugetlb_fault()) use them?

Thanks,
Naoya Horiguchi--
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