hugetlb: add comment for subtle SetHPageVmemmapOptimized()

The SetHPageVmemmapOptimized() called here seems unnecessary as it's
assumed to be set when calling this function. But it's indeed cleared
by above set_page_private(page, 0). Add a comment to avoid possible
future confusion.

Link: https://lkml.kernel.org/r/20220901120030.63318-9-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 29c3478d1bf37bc0d56dc100c6a685659de1f27d..fe7b69a970aa7dda1772fb7d8e766eab300d1652 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1504,6 +1504,10 @@ static void add_hugetlb_page(struct hstate *h, struct page *page,
 
        set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
        set_page_private(page, 0);
+       /*
+        * We have to set HPageVmemmapOptimized again as above
+        * set_page_private(page, 0) cleared it.
+        */
        SetHPageVmemmapOptimized(page);
 
        /*