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

[Mike Kravetz]

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@xxxxxxxxxxxxxxx>
> > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > ---
> >   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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