linux-kernel - [PATCH 04/34] mm, mmzone: clarify the usage of zone padding

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Message-Id: <1467970510-21195-5-git-send-email-mgorman@techsingularity.net>
Date:	Fri,  8 Jul 2016 10:34:40 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>
Cc:	Rik van Riel <riel@...riel.com>, Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 04/34] mm, mmzone: clarify the usage of zone padding

Zone padding separates write-intensive fields used by page allocation,
compaction and vmstats but the comments are a little misleading and
need clarification.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 include/linux/mmzone.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index d4f5cac0a8c3..edafdaf62e90 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -477,20 +477,21 @@ struct zone {
 	unsigned long		wait_table_hash_nr_entries;
 	unsigned long		wait_table_bits;
 
+	/* Write-intensive fields used from the page allocator */
 	ZONE_PADDING(_pad1_)
+
 	/* free areas of different sizes */
 	struct free_area	free_area[MAX_ORDER];
 
 	/* zone flags, see below */
 	unsigned long		flags;
 
-	/* Write-intensive fields used from the page allocator */
+	/* Primarily protects free_area */
 	spinlock_t		lock;
 
+	/* Write-intensive fields used by compaction and vmstats. */
 	ZONE_PADDING(_pad2_)
 
-	/* Write-intensive fields used by page reclaim */
-
 	/*
 	 * When free pages are below this point, additional steps are taken
 	 * when reading the number of free pages to avoid per-cpu counter
-- 
2.6.4