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@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Feilong Lin <linfeilong@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d91bd78..b1525ae 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5267,6 +5267,9 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
/*
* 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);