Re: [RFC PATCH 4/4] mm: madvise allow remove operation for hugetlbfs

Mike Kravetz
2015-04-17T17:11:56Z

On 04/17/2015 12:10 AM, Hillf Danton wrote:
>>
>> Now that we have hole punching support for hugetlbfs, we can
>> also support the MADV_REMOVE interface to it.
>>
>> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>> ---
>> mm/madvise.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/madvise.c b/mm/madvise.c
>> index d551475..c4a1027 100644
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -299,7 +299,7 @@ static long madvise_remove(struct vm_area_struct *vma,
>>
>> *prev = NULL; /* tell sys_madvise we drop mmap_sem */
>>
>> - if (vma->vm_flags & (VM_LOCKED | VM_HUGETLB))
>> + if (vma->vm_flags & VM_LOCKED)
>> return -EINVAL;
>>
>> f = vma->vm_file;
>> --
>> 2.1.0
>
> After the above change offset is computed,
>
> offset = (loff_t)(start - vma->vm_start)
> + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
>
> and I wonder if it is correct for huge page mapping.

I think it will be correct.

The above will be a (base) page size aligned offset into the file.
This offset will be huge page aligned in the fallocate hole punch
code.

/*
* For hole punch round up the beginning offset of the hole and
* round down the end.
*/
hole_start = (offset + hpage_size - 1) & ~huge_page_mask(h);
hole_end = (offset + len - (hpage_size - 1)) * ~huge_page_mask(h);

Was the alignment your concern, or something else?
--
Mike Kravetz