Re: [rfc][patch] radix-tree: small data structure

[Nick Piggin <nickpiggin@yahoo.com.au>]

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Nick Piggin wrote:
> With the previous patch, the radix_tree_node budget on my 64-bit
> desktop is cut from 20MB to 10MB. This patch should cut it again
> by nearly a factor of 4 (haven't verified, but 98ish % of files
> are under 64K).
> 
> I wonder if this would be of any interest for those who enable
> CONFIG_BASE_SMALL?

Bah, wrong patch.

-- 
SUSE Labs, Novell Inc.

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This patch reduces radix tree node memory usage by about a factor of 4
on many small files (< 64K) scenarios, and results in perfect packing of
the index range into 32 and 64 bits. There are pointer traversal and
memory usage costs for large files with dense pagecache.

Index: linux-2.6/lib/radix-tree.c
===================================================================
--- linux-2.6.orig/lib/radix-tree.c
+++ linux-2.6/lib/radix-tree.c
@@ -33,7 +33,7 @@
 
 
 #ifdef __KERNEL__
-#define RADIX_TREE_MAP_SHIFT	6
+#define RADIX_TREE_MAP_SHIFT	(CONFIG_BASE_SMALL ? 4 : 6)
 #else
 #define RADIX_TREE_MAP_SHIFT	3	/* For more stressful testing */
 #endif