linux-kernel - [RFC PATCH 2/4] mm: use mapcount for identifying zbud pages

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Message-id: <1377852176-30970-3-git-send-email-k.kozlowski@samsung.com>
Date:	Fri, 30 Aug 2013 10:42:54 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Bob Liu <bob.liu@...cle.com>, Mel Gorman <mgorman@...e.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Minchan Kim <minchan@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Subject: [RFC PATCH 2/4] mm: use mapcount for identifying zbud pages

Currently zbud pages do not have any flags set so it is not possible to
identify them during migration or compaction.

Implement PageZbud() by comparing page->_mapcount to -127 to distinguish
pages allocated by zbud. Just like PageBuddy() is implemented.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
---
 include/linux/mm.h |   23 +++++++++++++++++++++++
 mm/zbud.c          |    4 ++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f022460..b9ae6f2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -440,6 +440,7 @@ static inline void init_page_count(struct page *page)
  * efficiently by most CPU architectures.
  */
 #define PAGE_BUDDY_MAPCOUNT_VALUE (-128)
+#define PAGE_ZBUD_MAPCOUNT_VALUE (-127)
 
 static inline int PageBuddy(struct page *page)
 {
@@ -458,6 +459,28 @@ static inline void __ClearPageBuddy(struct page *page)
 	atomic_set(&page->_mapcount, -1);
 }
 
+#ifdef CONFIG_ZBUD
+static inline int PageZbud(struct page *page)
+{
+	return atomic_read(&page->_mapcount) == PAGE_ZBUD_MAPCOUNT_VALUE;
+}
+
+static inline void SetPageZbud(struct page *page)
+{
+	VM_BUG_ON(atomic_read(&page->_mapcount) != -1);
+	atomic_set(&page->_mapcount, PAGE_ZBUD_MAPCOUNT_VALUE);
+}
+
+static inline void ClearPageZbud(struct page *page)
+{
+	VM_BUG_ON(!PageZbud(page));
+	atomic_set(&page->_mapcount, -1);
+}
+#else
+PAGEFLAG_FALSE(Zbud)
+#endif
+
+
 void put_page(struct page *page);
 void put_pages_list(struct list_head *pages);
 
diff --git a/mm/zbud.c b/mm/zbud.c
index aa9a15c..9267cd9 100644
--- a/mm/zbud.c
+++ b/mm/zbud.c
@@ -197,7 +197,10 @@ static void get_zbud_page(struct zbud_header *zhdr)
 static int put_zbud_page(struct zbud_header *zhdr)
 {
 	struct page *page = virt_to_page(zhdr);
+	VM_BUG_ON(!PageZbud(page));
+
 	if (put_page_testzero(page)) {
+		ClearPageZbud(page);
 		free_hot_cold_page(page, 0);
 		return 1;
 	}
@@ -307,6 +310,7 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
 	 * don't increase the page count.
 	 */
 	zhdr = init_zbud_page(page);
+	SetPageZbud(page);
 	bud = FIRST;
 
 found:
-- 
1.7.9.5

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