linux-kernel - [PATCH 2/2] zsmalloc: micro-optimize zs_object

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Date:	Wed, 25 Mar 2015 00:24:47 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>
Cc:	Nitin Gupta <ngupta@...are.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH 2/2] zsmalloc: micro-optimize zs_object_copy()

A micro-optimization. Avoid additional branching and reduce
(a bit) registry pressure (f.e. s_off += size; d_off += size;
may be calculated twise: first for >= PAGE_SIZE check and later
for offset update in "else" clause).

/scripts/bloat-o-meter shows some improvement

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-10 (-10)
function                          old     new   delta
zs_object_copy                    550     540     -10

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 mm/zsmalloc.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 7af4456..dc35328 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1535,28 +1535,27 @@ static void zs_object_copy(unsigned long src, unsigned long dst,
 		if (written == class->size)
 			break;
 
-		if (s_off + size >= PAGE_SIZE) {
+		s_off += size;
+		s_size -= size;
+		d_off += size;
+		d_size -= size;
+
+		if (s_off >= PAGE_SIZE) {
 			kunmap_atomic(s_addr);
 			s_page = get_next_page(s_page);
 			BUG_ON(!s_page);
 			s_addr = kmap_atomic(s_page);
 			s_size = class->size - written;
 			s_off = 0;
-		} else {
-			s_off += size;
-			s_size -= size;
 		}
 
-		if (d_off + size >= PAGE_SIZE) {
+		if (d_off >= PAGE_SIZE) {
 			kunmap_atomic(d_addr);
 			d_page = get_next_page(d_page);
 			BUG_ON(!d_page);
 			d_addr = kmap_atomic(d_page);
 			d_size = class->size - written;
 			d_off = 0;
-		} else {
-			d_off += size;
-			d_size -= size;
 		}
 	}
 
-- 
2.3.4

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