Re: [PATCH V2] mm/hugetlb.c: fix unnecessary address expansion of pmd sharing

[Mike Kravetz <mike.kravetz@oracle.com>]

On 1/4/21 12:16 AM, Li Xinhai wrote:
> The current code would unnecessarily expand the address range. Consider
> one example, (start, end) = (1G-2M, 3G+2M), and (vm_start, vm_end) =
> (1G-4M, 3G+4M), the expected adjustment should be keep (1G-2M, 3G+2M)
> without expand. But the current result will be (1G-4M, 3G+4M). Actually,
> the range (1G-4M, 1G) and (3G, 3G+4M) would never been involved in pmd
> sharing.
> 
> After this patch, we will check that the vma span at least one PUD
> aligned size and the start,end range overlap the aligned range of vma.
> 
> With above example, the aligned vma range is (1G, 3G), so if (start, end)
> range is within (1G-4M, 1G), or within (3G, 3G+4M), then no adjustment
> to both start and end. Otherwise, we will have chance to adjust start
> downwards or end upwards without exceeding (vm_start, vm_end).
> 
> Fixes: 75802ca66354 ("mm/hugetlb: fix calculation of adjust_range_if_pmd_sharing_possible")
> Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Peter Xu <peterx@redhat.com>
> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> ---

Thanks again.  Comments and discussion in previous thread.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz