From 8dfcc9ba27e2ed257e5de9539f7f03e57c2c0e33 Mon Sep 17 00:00:00 2001
From: Nick Piggin <npiggin@suse.de>
Date: Wed, 22 Mar 2006 00:08:05 -0800
Subject: [PATCH] mm: split highorder pages

Have an explicit mm call to split higher order pages into individual pages.
 Should help to avoid bugs and be more explicit about the code's intention.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
 mm/page_alloc.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'mm/page_alloc.c')

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 102919851353..fc65e87368b3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -752,6 +752,28 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
 		clear_highpage(page + i);
 }
 
+#ifdef CONFIG_MMU
+/*
+ * split_page takes a non-compound higher-order page, and splits it into
+ * n (1<<order) sub-pages: page[0..n]
+ * Each sub-page must be freed individually.
+ *
+ * Note: this is probably too low level an operation for use in drivers.
+ * Please consult with lkml before using this in your driver.
+ */
+void split_page(struct page *page, unsigned int order)
+{
+	int i;
+
+	BUG_ON(PageCompound(page));
+	BUG_ON(!page_count(page));
+	for (i = 1; i < (1 << order); i++) {
+		BUG_ON(page_count(page + i));
+		set_page_count(page + i, 1);
+	}
+}
+#endif
+
 /*
  * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch
-- 
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