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

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Date:	Fri, 17 Apr 2015 10:11:41 -0700
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	Hillf Danton <hillf.zj@...baba-inc.com>,
	"'Dave Hansen'" <dave.hansen@...ux.intel.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [RFC PATCH 4/4] mm: madvise allow remove operation for hugetlbfs

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@...ux.intel.com>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.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
--
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