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authorNamhyung Kim <namhyung@gmail.com>2010-09-16 01:30:19 +0900
committerJiri Kosina <jkosina@suse.cz>2010-09-23 13:52:38 +0200
commited9f524ac79457f0c547c85746b19b92526be612 (patch)
tree9cc0900a65c3361faa5b25a4a7415ca6b415c40a
parent72b43570f304634532b4d66c991eef529135f68c (diff)
ida: document IDA_BITMAP_LONGS calculation
IDA_BITMAP_LONGS value is calculated take into account struct ida_bitmap not to waste memory space. Comment it. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
-rw-r--r--include/linux/idr.h7
1 files changed, 5 insertions, 2 deletions
diff --git a/include/linux/idr.h b/include/linux/idr.h
index e968db71e33a..88607523e2df 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -117,10 +117,13 @@ void idr_init(struct idr *idp);
/*
* IDA - IDR based id allocator, use when translation from id to
* pointer isn't necessary.
+ *
+ * IDA_BITMAP_LONGS is calculated to be one less to accommodate
+ * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
*/
#define IDA_CHUNK_SIZE 128 /* 128 bytes per chunk */
-#define IDA_BITMAP_LONGS (128 / sizeof(long) - 1)
-#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)
+#define IDA_BITMAP_LONGS (IDA_CHUNK_SIZE / sizeof(long) - 1)
+#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)
struct ida_bitmap {
long nr_busy;