linux-kernel - [PATCH v2 2/6] mm/debug_pagealloc: don't allocate page

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Date:	Tue, 16 Aug 2016 11:51:15 +0900
From:	js1304@...il.com
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Minchan Kim <minchan@...nel.org>,
	Michal Hocko <mhocko@...nel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v2 2/6] mm/debug_pagealloc: don't allocate page_ext if we don't use guard page

From: Joonsoo Kim <iamjoonsoo.kim@....com>

What debug_pagealloc does is just mapping/unmapping page table.
Basically, it doesn't need additional memory space to memorize something.
But, with guard page feature, it requires additional memory to distinguish
if the page is for guard or not. Guard page is only used when
debug_guardpage_minorder is non-zero so this patch removes additional
memory allocation (page_ext) if debug_guardpage_minorder is zero.

It saves memory if we just use debug_pagealloc and not guard page.

Acked-by: Vlastimil Babka <vbabka@...e.cz>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 mm/page_alloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5e7944b..45cb021 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -608,6 +608,9 @@ static bool need_debug_guardpage(void)
 	if (!debug_pagealloc_enabled())
 		return false;
 
+	if (!debug_guardpage_minorder())
+		return false;
+
 	return true;
 }
 
@@ -616,6 +619,9 @@ static void init_debug_guardpage(void)
 	if (!debug_pagealloc_enabled())
 		return;
 
+	if (!debug_guardpage_minorder())
+		return;
+
 	_debug_guardpage_enabled = true;
 }
 
@@ -636,7 +642,7 @@ static int __init debug_guardpage_minorder_setup(char *buf)
 	pr_info("Setting debug_guardpage_minorder to %lu\n", res);
 	return 0;
 }
-__setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
+early_param("debug_guardpage_minorder", debug_guardpage_minorder_setup);
 
 static inline bool set_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype)
-- 
1.9.1