From: Miaohe Lin <linmiaohe@xxxxxxxxxx> Subject: mm/hugeltb: clarify (chg - freed) won't go negative in hugetlb_unreserve_pages() The resv_map could be NULL since this routine can be called in the evict inode path for all hugetlbfs inodes and we will have chg = 0 in this case. But (chg - freed) won't go negative as Mike pointed out: "If resv_map is NULL, then no hugetlb pages can be allocated/associated with the file. As a result, remove_inode_hugepages will never find any huge pages associated with the inode and the passed value 'freed' will always be zero." Add a comment clarifying this to make it clear and also avoid confusion. Link: https://lkml.kernel.org/r/20210410072348.20437-4-linmiaohe@xxxxxxxxxx Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Feilong Lin <linfeilong@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/hugetlb.c~mm-hugeltb-clarify-chg-freed-wont-go-negative-in-hugetlb_unreserve_pages +++ a/mm/hugetlb.c @@ -5267,6 +5267,9 @@ long hugetlb_unreserve_pages(struct inod /* * If the subpool has a minimum size, the number of global * reservations to be released may be adjusted. + * + * Note that !resv_map implies freed == 0. So (chg - freed) + * won't go negative. */ gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed)); hugetlb_acct_memory(h, -gbl_reserve); _
