mm/page_alloc: minor clean up for memmap_init_compound()

Since commit 5232c63f46fd ("mm: Make compound_pincount always available"),
compound_pincount_ptr is stored at first tail page now.  So we should call
prep_compound_head() after the first tail page is initialized to take
advantage of the likelihood of that tail struct page being cached given
that we will read them right after in prep_compound_head().

Link: https://lkml.kernel.org/r/20220611021352.13529-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 63f1cffa09f7bd34d400bd9ea52b15a533875ab7..19a0e4a23b2f1c36b322b9e8c913e60306c619c4 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6811,13 +6811,18 @@ static void __ref memmap_init_compound(struct page *head,
                set_page_count(page, 0);
 
                /*
-                * The first tail page stores compound_mapcount_ptr() and
-                * compound_order() and the second tail page stores
-                * compound_pincount_ptr(). Call prep_compound_head() after
-                * the first and second tail pages have been initialized to
-                * not have the data overwritten.
+                * The first tail page stores compound_mapcount_ptr(),
+                * compound_order() and compound_pincount_ptr(). Call
+                * prep_compound_head() after the first tail page have
+                * been initialized to not have the data overwritten.
+                *
+                * Note the idea to make this right after we initialize
+                * the offending tail pages is trying to take advantage
+                * of the likelihood of those tail struct pages being
+                * cached given that we will read them right after in
+                * prep_compound_head().
                 */
-               if (pfn == head_pfn + 2)
+               if (unlikely(pfn == head_pfn + 1))
                        prep_compound_head(head, order);
        }
 }