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

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Date:	Sat, 18 Apr 2015 09:16:53 -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 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@...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?

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
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