On Wed, Oct 19, 2016 at 01:24:26PM -0400, Johannes Weiner wrote:
> Add an internal tag to identify special entries that are accounted in
> node->special in addition to node->count.
>
> With this in place, the next patch can restore refault detection in
> single-page files. It will also move the shadow count from the upper
> bits of count to the new special counter, and then shrink count to a
> char as well; the growth of struct radix_tree_node is temporary.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> include/linux/radix-tree.h | 10 ++++++----
> lib/radix-tree.c | 14 ++++++++++----
> 2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 756b2909467e..2e1c9added23 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -68,7 +68,8 @@ enum radix_tree_tags {
> /* Freely allocatable radix tree user tags */
> RADIX_TREE_NR_USER_TAGS = 3,
> /* Radix tree internal tags */
> - RADIX_TREE_NR_TAGS = RADIX_TREE_NR_USER_TAGS,
> + RADIX_TREE_TAG_SPECIAL = RADIX_TREE_NR_USER_TAGS,
> + RADIX_TREE_NR_TAGS,
> };
>
> #ifndef RADIX_TREE_MAP_SHIFT
> @@ -90,9 +91,10 @@ enum radix_tree_tags {
> #define RADIX_TREE_COUNT_MASK ((1UL << RADIX_TREE_COUNT_SHIFT) - 1)
>
> struct radix_tree_node {
> - unsigned char shift; /* Bits remaining in each slot */
> - unsigned char offset; /* Slot offset in parent */
> - unsigned int count;
> + unsigned char shift; /* Bits remaining in each slot */
> + unsigned char offset; /* Slot offset in parent */
> + unsigned int count; /* Total entry count */
> + unsigned char special; /* Special entry count */
How about putting the new char field into the implicit hole between
offset and count? pahole is your friend here:
struct radix_tree_node {
unsigned char shift; /* 0 1 */
unsigned char offset; /* 1 1 */
/* XXX 2 bytes hole, try to pack */
unsigned int count; /* 4 4 */
.....
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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