From: Miaohe Lin <linmiaohe@xxxxxxxxxx> 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/20210318122722.13135-3-linmiaohe@xxxxxxxxxx Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michel Lespinasse <walken@xxxxxxxxxx> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> Cc: Thomas Hellstrm (Intel) <thomas_os@xxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> Cc: William Kucharski <william.kucharski@xxxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Cc: yuleixzhang <yulei.kernel@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- 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) _
