[023/143] mm/huge_memory.c: make get_huge_zero_page() return bool

Commit Message

Andrew Morton May 5, 2021, 1:33 a.m. UTC

From: Miaohe Lin <[e-mail]>
Subject: mm/huge_memory.c: make get_huge_zero_page() return bool

It's guaranteed that huge_zero_page will not be NULL if huge_zero_refcount
is increased successfully.  When READ_ONCE(huge_zero_page) is returned,
there must be a huge_zero_page and it can be replaced with returning
'true' when we do not care about the value of huge_zero_page.  We can thus
make it return bool to save READ_ONCE cpu cycles as the return value is
just used to check if huge_zero_page exists.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Miaohe Lin <[e-mail]>
Reviewed-by: Zi Yan <[e-mail]>
Reviewed-by: Peter Xu <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Michel Lespinasse <[e-mail]>
Cc: Ralph Campbell <[e-mail]>
Cc: Thomas Hellstrm (Intel) <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Wei Yang <[e-mail]>
Cc: William Kucharski <[e-mail]>
Cc: Yang Shi <[e-mail]>
Cc: yuleixzhang <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/huge_memory.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Patch

--- a/mm/huge_memory.c~mm-huge_memoryc-make-get_huge_zero_page-return-bool
+++ a/mm/huge_memory.c
@@ -77,18 +77,18 @@  bool transparent_hugepage_enabled(struct
 	return false;
 }
 
-static struct page *get_huge_zero_page(void)
+static bool get_huge_zero_page(void)
 {
 	struct page *zero_page;
 retry:
 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
-		return READ_ONCE(huge_zero_page);
+		return true;
 
 	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 			HPAGE_PMD_ORDER);
 	if (!zero_page) {
 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
-		return NULL;
+		return false;
 	}
 	count_vm_event(THP_ZERO_PAGE_ALLOC);
 	preempt_disable();
@@ -101,7 +101,7 @@  retry:
 	/* We take additional reference here. It will be put back by shrinker */
 	atomic_set(&huge_zero_refcount, 2);
 	preempt_enable();
-	return READ_ONCE(huge_zero_page);
+	return true;
 }
 
 static void put_huge_zero_page(void)