mm: Use fixed constant in page_frag_alloc instead of size + 1 (86447726) · Commits · e / devices / android_kernel_fairphone_FP5

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: ("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>

mm/page_alloc.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}