Re: [PATCH 2/4] hugetlg: Break earlier in add_reservation_in_range() when we can

Mike Kravetz
2021-02-04T00:49:05Z

On 2/3/21 1:08 PM, Peter Xu wrote:
> All the regions maintained in hugetlb reserved map is inclusive on "from" but
> exclusive on "to". We can break earlier even if rg->from==t because it already
> means no possible intersection.
>
> This does not need a Fixes in all cases because when it happens (rg->from==t)
> we'll not break out of the loop while we should, however the next thing we'd do
> is still add the last file_region we'd need and quit the loop in the next
> round. So this change is not a bugfix (since the old code should still run
> okay iiuc), but we'd better still touch it up to make it logically sane.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/hugetlb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index d2859c2aecc9..9e6ea96bf33b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -377,7 +377,7 @@ static long add_reservation_in_range(struct resv_map *resv, long f, long t,
> /* When we find a region that starts beyond our range, we've
> * finished.
> */
> - if (rg->from > t)
> + if (rg->from >= t)
> break;
>
> /* Add an entry for last_accounted_offset -> rg->from, and
>

Changing any of this code makes me nervous. However, I agree with your
analysis. The change makes the code match the comment WRT the [from, to)
nature of regions.

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