The patch titled
fix the max path calculation in radix-tree.c
has been added to the -mm tree. Its filename is
fix-the-max-path-calculation-in-radix-treec.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: fix the max path calculation in radix-tree.c
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
A while back, Nick Piggin introduced a patch to reduce the node memory
usage for small files (commit cfd9b7df4abd3257c9e381b0e445817b26a51c0c):
-#define RADIX_TREE_MAP_SHIFT 6
+#define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
Unfortunately, he didn't take into account the fact that the
calculation of the maximum path was based on an assumption of having
to round up:
#define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
So, if CONFIG_BASE_SMALL is set, you will end up with a
RADIX_TREE_MAX_PATH that is one greater than necessary. The practical
upshot of this is just a bit of wasted memory (one long in the
height_to_maxindex array, an extra pre-allocated radix tree node per
cpu, and extra stack usage in a couple of functions), but it seems
worth getting right.
It's also worth noting that I never build with CONFIG_BASE_SMALL.
What I did to test this was duplicate the code in a small user-space
program and check the results of the calculations for max path and the
contents of the height_to_maxindex array.
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/radix-tree.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletion(-)
diff -puN lib/radix-tree.c~fix-the-max-path-calculation-in-radix-treec lib/radix-tree.c
--- a/lib/radix-tree.c~fix-the-max-path-calculation-in-radix-treec
+++ a/lib/radix-tree.c
@@ -60,7 +60,8 @@ struct radix_tree_path {
};
#define RADIX_TREE_INDEX_BITS (8 /* CHAR_BIT */ * sizeof(unsigned long))
-#define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
+#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
+ RADIX_TREE_MAP_SHIFT) + 1)
static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH] __read_mostly;
_
Patches currently in -mm which might be from jmoyer@xxxxxxxxxx are
fix-the-max-path-calculation-in-radix-treec.patch
aio-account-i-o-wait-time-properly.patch
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