Btrfs: reduce size of struct extent_state

The tree field of struct extent_state was only used to figure out if
an extent state was connected to an inode's io tree or not. For this
we can just use the rb_node field itself.

On a x86_64 system with this change the sizeof(struct extent_state) is
reduced from 96 bytes down to 88 bytes, meaning that with a page size
of 4096 bytes we can now store 46 extent states per page instead of 42.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 20 insertions, 17 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1009fa8a08ef..816e80e678bd 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -25,6 +25,11 @@ static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
 static struct bio_set *btrfs_bioset;
 
+static inline bool extent_state_in_tree(const struct extent_state *state)
+{
+        return !RB_EMPTY_NODE(&state->rb_node);
+}
+
 #ifdef CONFIG_BTRFS_DEBUG
 static LIST_HEAD(buffers);
 static LIST_HEAD(states);
@@ -59,9 +64,9 @@ void btrfs_leak_debug_check(void)
 
         while (!list_empty(&states)) {
                 state = list_entry(states.next, struct extent_state, leak_list);
-                printk(KERN_ERR "BTRFS: state leak: start %llu end %llu "
-                       "state %lu in tree %p refs %d\n",
-                       state->start, state->end, state->state, state->tree,
+                pr_err("BTRFS: state leak: start %llu end %llu state %lu in tree %d refs %d\n",
+                       state->start, state->end, state->state,
+                       extent_state_in_tree(state),
                        atomic_read(&state->refs));
                 list_del(&state->leak_list);
                 kmem_cache_free(extent_state_cache, state);
@@ -209,7 +214,7 @@ static struct extent_state *alloc_extent_state(gfp_t mask)
                 return state;
         state->state = 0;
         state->private = 0;
-        state->tree = NULL;
+        RB_CLEAR_NODE(&state->rb_node);
         btrfs_leak_debug_add(&state->leak_list, &states);
         atomic_set(&state->refs, 1);
         init_waitqueue_head(&state->wq);
@@ -222,7 +227,7 @@ void free_extent_state(struct extent_state *state)
         if (!state)
                 return;
         if (atomic_dec_and_test(&state->refs)) {
-                WARN_ON(state->tree);
+                WARN_ON(extent_state_in_tree(state));
                 btrfs_leak_debug_del(&state->leak_list);
                 trace_free_extent_state(state, _RET_IP_);
                 kmem_cache_free(extent_state_cache, state);
@@ -371,8 +376,8 @@ static void merge_state(struct extent_io_tree *tree,
                     other->state == state->state) {
                         merge_cb(tree, state, other);
                         state->start = other->start;
-                        other->tree = NULL;
                         rb_erase(&other->rb_node, &tree->state);
+                        RB_CLEAR_NODE(&other->rb_node);
                         free_extent_state(other);
                 }
         }
@@ -383,8 +388,8 @@ static void merge_state(struct extent_io_tree *tree,
                     other->state == state->state) {
                         merge_cb(tree, state, other);
                         state->end = other->end;
-                        other->tree = NULL;
                         rb_erase(&other->rb_node, &tree->state);
+                        RB_CLEAR_NODE(&other->rb_node);
                         free_extent_state(other);
                 }
         }
@@ -442,7 +447,6 @@ static int insert_state(struct extent_io_tree *tree,
                        found->start, found->end, start, end);
                 return -EEXIST;
         }
-        state->tree = tree;
         merge_state(tree, state);
         return 0;
 }
@@ -486,7 +490,6 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
                 free_extent_state(prealloc);
                 return -EEXIST;
         }
-        prealloc->tree = tree;
         return 0;
 }
 
@@ -524,9 +527,9 @@ static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
                 wake_up(&state->wq);
         if (state->state == 0) {
                 next = next_state(state);
-                if (state->tree) {
+                if (extent_state_in_tree(state)) {
                         rb_erase(&state->rb_node, &tree->state);
-                        state->tree = NULL;
+                        RB_CLEAR_NODE(&state->rb_node);
                         free_extent_state(state);
                 } else {
                         WARN_ON(1);
@@ -606,8 +609,8 @@ again:
                         cached_state = NULL;
                 }
 
-                if (cached && cached->tree && cached->start <= start &&
-                    cached->end > start) {
+                if (cached && extent_state_in_tree(cached) &&
+                    cached->start <= start && cached->end > start) {
                         if (clear)
                                 atomic_dec(&cached->refs);
                         state = cached;
@@ -843,7 +846,7 @@ again:
         if (cached_state && *cached_state) {
                 state = *cached_state;
                 if (state->start <= start && state->end > start &&
-                    state->tree) {
+                    extent_state_in_tree(state)) {
                         node = &state->rb_node;
                         goto hit_next;
                 }
@@ -1069,7 +1072,7 @@ again:
         if (cached_state && *cached_state) {
                 state = *cached_state;
                 if (state->start <= start && state->end > start &&
-                    state->tree) {
+                    extent_state_in_tree(state)) {
                         node = &state->rb_node;
                         goto hit_next;
                 }
@@ -1459,7 +1462,7 @@ int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
         spin_lock(&tree->lock);
         if (cached_state && *cached_state) {
                 state = *cached_state;
-                if (state->end == start - 1 && state->tree) {
+                if (state->end == start - 1 && extent_state_in_tree(state)) {
                         n = rb_next(&state->rb_node);
                         while (n) {
                                 state = rb_entry(n, struct extent_state,
@@ -1905,7 +1908,7 @@ int test_range_bit(struct extent_io_tree *tree, u64 start, u64 end,
         int bitset = 0;
 
         spin_lock(&tree->lock);
-        if (cached && cached->tree && cached->start <= start &&
+        if (cached && extent_state_in_tree(cached) && cached->start <= start &&
             cached->end > start)
                 node = &cached->rb_node;
         else