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

Mike Kravetz
2015-04-18T16:17:13Z

On 04/17/2015 10:11 AM, Mike Kravetz wrote:
> 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?

Well, that alignment code in fallocate hole punch obviously wrong. :(
Sorry about that. I'll send out an updated RFC with working hole punch.

--
Mike Kravetz