mm/page_alloc: update comments in __free_pages_ok()

Add a comment to explain why we call get_pfnblock_migratetype() twice in
__free_pages_ok().

Link: https://lkml.kernel.org/r/20221201135045.31663-1-wonder_rock@126.com
Signed-off-by: Deyan Wang <wonder_rock@126.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5ab9dd2..0745aed 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1702,6 +1702,11 @@ static void __free_pages_ok(struct page *page, unsigned int order,
        if (!free_pages_prepare(page, order, true, fpi_flags))
                return;
 
+       /*
+        * Calling get_pfnblock_migratetype() without spin_lock_irqsave() here
+        * is used to avoid calling get_pfnblock_migratetype() under the lock.
+        * This will reduce the lock holding time.
+        */
        migratetype = get_pfnblock_migratetype(page, pfn);
 
        spin_lock_irqsave(&zone->lock, flags);