On 1/26/21 3:55 AM, Miaohe Lin wrote:
> When subpool max_hpages accounting is not enabled, used_hpages is always 0
> and might lead to release subpool prematurely because it indicates no pages
> are used now while there might be.
It might be good to say that you need min_hpages accounting (min_size mount
option) enabled for this issue to occur. Or, perhaps say this is possible
if a hugetlbfs filesystem is created with the min_size option and without
the size option.
That might better explain the conditions in which a user could see the issue.
> In order to fix this issue, we should check used_hpages == 0 iff max_hpages
> accounting is enabled. As max_hpages accounting should be enabled in most
> common case, this is not worth a Cc stable.
I agree that such a combination of mount options is very uncommon.
>
> Signed-off-by: Hongxiang Lou <louhongxiang@xxxxxxxxxx>
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> mm/hugetlb.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
Thanks,
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
--
Mike Kravetz
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 777bc0e45bf3..53ea65d1c5ab 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -97,16 +97,26 @@ static inline void ClearPageHugeFreed(struct page *head)
> /* Forward declaration */
> static int hugetlb_acct_memory(struct hstate *h, long delta);
>
> -static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
> +static inline bool subpool_is_free(struct hugepage_subpool *spool)
> {
> - bool free = (spool->count == 0) && (spool->used_hpages == 0);
> + if (spool->count)
> + return false;
> + if (spool->max_hpages != -1)
> + return spool->used_hpages == 0;
> + if (spool->min_hpages != -1)
> + return spool->rsv_hpages == spool->min_hpages;
>
> + return true;
> +}
> +
> +static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
> +{
> spin_unlock(&spool->lock);
>
> /* If no pages are used, and no other handles to the subpool
> * remain, give up any reservations based on minimum size and
> * free the subpool */
> - if (free) {
> + if (subpool_is_free(spool)) {
> if (spool->min_hpages != -1)
> hugetlb_acct_memory(spool->hstate,
> -spool->min_hpages);
>
