Commit 69598616 authored Feb 15, 2019 by Alexander Duyck Committed by Greg Kroah-Hartman Apr 17, 2020

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

commit 8644772637deb121f7ac2df690cbf83fa63d3b70 upstream.

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>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 2e22edcd

mm/page_alloc.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -4537,11 +4537,11 @@ 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;
		}

		@@ -4557,10 +4557,10 @@ 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;
		}