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/20210318122722.13135-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Thomas Hellstrm (Intel) <thomas_os@shipmail.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: yuleixzhang <yulei.kernel@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ae16a82da823303b93b3effd5b09c0461bc27cc2..01b96c638e7364f3d77198896e13bd3875cc09ea 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -77,18 +77,18 @@ bool transparent_hugepage_enabled(struct vm_area_struct *vma)
        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)