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

[Mike Kravetz <mike.kravetz@oracle.com>]

On 05/21/2015 11:23 PM, Naoya Horiguchi wrote:
> 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@oracle.com>
>> ---
>>   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?
> 

I will make that change in the next version of the patch set.

Thanks,
-- 
Mike Kravetz


> Thanks,
> Naoya Horiguchi
> 

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