ida: Use exceptional entries for small IDAs
We can use the root entry as a bitmap and save allocating a 128 byte
bitmap for an IDA that contains only a few entries (30 on a 32-bit
machine, 62 on a 64-bit machine). This costs about 300 bytes of kernel
text on x86-64, so as long as 3 IDAs fall into this category, this
is a net win for memory consumption.
Thanks to Rasmus Villemoes for his work documenting the problem and
collecting statistics on IDAs.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7b9f851..14130ab 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -338,6 +338,14 @@
for (i = 0; i < RADIX_TREE_MAP_SIZE; i++)
dump_ida_node(node->slots[i],
index | (i << node->shift));
+ } else if (radix_tree_exceptional_entry(entry)) {
+ pr_debug("ida excp: %p offset %d indices %lu-%lu data %lx\n",
+ entry, (int)(index & RADIX_TREE_MAP_MASK),
+ index * IDA_BITMAP_BITS,
+ index * IDA_BITMAP_BITS + BITS_PER_LONG -
+ RADIX_TREE_EXCEPTIONAL_SHIFT,
+ (unsigned long)entry >>
+ RADIX_TREE_EXCEPTIONAL_SHIFT);
} else {
struct ida_bitmap *bitmap = entry;