linux-kernel - [PATCH 5/6] mm, page_alloc: pull out side effects from free_pages

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Date:	Wed, 27 Apr 2016 15:57:22 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 5/6] mm, page_alloc: pull out side effects from free_pages_check

Check without side-effects should be easier to maintain. It also removes the
duplicated cpupid and flags reset done in !DEBUG_VM variant of both
free_pcp_prepare() and then bulkfree_pcp_prepare(). Finally, it enables
the next patch.

It shouldn't result in new branches, thanks to inlining of the check.

!DEBUG_VM bloat-o-meter:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-27 (-27)
function                                     old     new   delta
__free_pages_ok                              748     739      -9
free_pcppages_bulk                          1403    1385     -18

DEBUG_VM:

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-28 (-28)
function                                     old     new   delta
free_pages_prepare                           806     778     -28

This is also slightly faster because cpupid information is not set on tail
pages so we can avoid resets there.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 97894cbe2fa3..b823f00c275b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -932,11 +932,8 @@ static void free_pages_check_bad(struct page *page)
 }
 static inline int free_pages_check(struct page *page)
 {
-	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE))) {
-		page_cpupid_reset_last(page);
-		page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE)))
 		return 0;
-	}
 
 	/* Something has gone sideways, find it */
 	free_pages_check_bad(page);
@@ -1016,7 +1013,11 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 		for (i = 1; i < (1 << order); i++) {
 			if (compound)
 				bad += free_tail_pages_check(page, page + i);
-			bad += free_pages_check(page + i);
+			if (unlikely(free_pages_check(page + i))) {
+				bad++;
+				continue;
+			}
+			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
 	if (PageAnonHead(page))
@@ -1025,6 +1026,8 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 	if (bad)
 		return false;
 
+	page_cpupid_reset_last(page);
+	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 	reset_page_owner(page, order);
 
 	if (!PageHighMem(page)) {
-- 
2.6.4