mm: Use fixed constant in page_frag_alloc instead of size + 1

This patch replaces the size + 1 value introduced with the recent fix for 1
byte allocs with a constant value.

The idea here is to reduce code overhead as the previous logic would have
to read size into a register, then increment it, and write it back to
whatever field was being used. By using a constant we can avoid those
memory reads and arithmetic operations in favor of just encoding the
maximum value into the operation itself.

Fixes: 2c2ade81741c ("mm: page_alloc: fix ref bias in page_frag_alloc() for 1-byte allocs")
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 46285d28e43b529b333dbd8c3b3cf0123df66417..7f79b78bc8294557480a6df4fdb328f757895a7d 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4675,11 +4675,11 @@ void *page_frag_alloc(struct page_frag_cache *nc,
                /* Even if we own the page, we do not use atomic_set().
                 * This would break get_page_unless_zero() users.
                 */
-               page_ref_add(page, size);
+               page_ref_add(page, PAGE_FRAG_CACHE_MAX_SIZE);
 
                /* reset page count bias and offset to start of new frag */
                nc->pfmemalloc = page_is_pfmemalloc(page);
-               nc->pagecnt_bias = size + 1;
+               nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
                nc->offset = size;
        }
 
@@ -4695,10 +4695,10 @@ void *page_frag_alloc(struct page_frag_cache *nc,
                size = nc->size;
 #endif
                /* OK, page count is 0, we can safely set it */
-               set_page_count(page, size + 1);
+               set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
 
                /* reset page count bias and offset to start of new frag */
-               nc->pagecnt_bias = size + 1;
+               nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
                offset = size - fragsz;
        }