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authorNick Piggin <npiggin@suse.de>2006-03-22 00:08:05 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-22 07:53:57 -0800
commit8dfcc9ba27e2ed257e5de9539f7f03e57c2c0e33 (patch)
treeaecaeb6a0b33c23f79dfcd2418e4a3881a29f2e2 /mm
parent8e7a9aae91101916b86de07fafe3272ea8dc1f10 (diff)
[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>
Diffstat (limited to 'mm')
-rw-r--r--mm/memory.c4
-rw-r--r--mm/page_alloc.c22
2 files changed, 23 insertions, 3 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 85e80a57db2..6af555c1c42 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1221,9 +1221,7 @@ out:
* The page has to be a nice clean _individual_ kernel allocation.
* If you allocate a compound page, you need to have marked it as
* such (__GFP_COMP), or manually just split the page up yourself
- * (which is mainly an issue of doing "set_page_count(page, 1)" for
- * each sub-page, and then freeing them one by one when you free
- * them rather than freeing it as a compound page).
+ * (see split_page()).
*
* NOTE! Traditionally this was done with "remap_pfn_range()" which
* took an arbitrary page protection parameter. This doesn't allow
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 10291985135..fc65e87368b 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