Btrfs: leave btree locks spinning more often

btrfs_mark_buffer dirty would set dirty bits in the extent_io tree
for the buffers it was dirtying.  This may require a kmalloc and it
was not atomic.  So, anyone who called btrfs_mark_buffer_dirty had to
set any btree locks they were holding to blocking first.

This commit changes dirty tracking for extent buffers to just use a flag
in the extent buffer.  Now that we have one and only one extent buffer
per page, this can be safely done without losing dirty bits along the way.

This also introduces a path->leave_spinning flag that callers of
btrfs_search_slot can use to indicate they will properly deal with a
path returned where all the locks are spinning instead of blocking.

Many of the btree search callers now expect spinning paths,
resulting in better btree concurrency overall.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 50 insertions, 19 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a421c32c6cfe..8933d15a240f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -56,9 +56,6 @@ static int __btrfs_alloc_reserved_extent(struct btrfs_trans_handle *trans,
                                          int ref_mod);
 static int update_reserved_extents(struct btrfs_root *root,
                                    u64 bytenr, u64 num, int reserve);
-static int pin_down_bytes(struct btrfs_trans_handle *trans,
-                          struct btrfs_root *root,
-                          u64 bytenr, u64 num_bytes, int is_data);
 static int update_block_group(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               u64 bytenr, u64 num_bytes, int alloc,
@@ -618,6 +615,7 @@ static noinline int insert_extent_backref(struct btrfs_trans_handle *trans,
         } else {
                 goto out;
         }
+        btrfs_unlock_up_safe(path, 1);
         btrfs_mark_buffer_dirty(path->nodes[0]);
 out:
         btrfs_release_path(root, path);
@@ -760,6 +758,7 @@ static noinline_for_stack int add_extent_ref(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
 
         path->reada = 1;
+        path->leave_spinning = 1;
         key.objectid = bytenr;
         key.type = BTRFS_EXTENT_ITEM_KEY;
         key.offset = num_bytes;
@@ -767,8 +766,10 @@ static noinline_for_stack int add_extent_ref(struct btrfs_trans_handle *trans,
         /* first find the extent item and update its reference count */
         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key,
                                 path, 0, 1);
-        if (ret < 0)
+        if (ret < 0) {
+                btrfs_set_path_blocking(path);
                 return ret;
+        }
 
         if (ret > 0) {
                 WARN_ON(1);
@@ -791,11 +792,15 @@ static noinline_for_stack int add_extent_ref(struct btrfs_trans_handle *trans,
 
         refs = btrfs_extent_refs(l, item);
         btrfs_set_extent_refs(l, item, refs + refs_to_add);
+        btrfs_unlock_up_safe(path, 1);
+
         btrfs_mark_buffer_dirty(path->nodes[0]);
 
         btrfs_release_path(root->fs_info->extent_root, path);
 
         path->reada = 1;
+        path->leave_spinning = 1;
+
         /* now insert the actual backref */
         ret = insert_extent_backref(trans, root->fs_info->extent_root,
                                     path, bytenr, parent,
@@ -2050,6 +2055,8 @@ int btrfs_update_pinned_extents(struct btrfs_root *root,
                 clear_extent_dirty(&fs_info->pinned_extents,
                                 bytenr, bytenr + num - 1, GFP_NOFS);
         }
+        mutex_unlock(&root->fs_info->pinned_mutex);
+
         while (num > 0) {
                 cache = btrfs_lookup_block_group(fs_info, bytenr);
                 BUG_ON(!cache);
@@ -2141,8 +2148,8 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
         u64 end;
         int ret;
 
-        mutex_lock(&root->fs_info->pinned_mutex);
         while (1) {
+                mutex_lock(&root->fs_info->pinned_mutex);
                 ret = find_first_extent_bit(unpin, 0, &start, &end,
                                             EXTENT_DIRTY);
                 if (ret)
@@ -2150,14 +2157,11 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
 
                 ret = btrfs_discard_extent(root, start, end + 1 - start);
 
+                /* unlocks the pinned mutex */
                 btrfs_update_pinned_extents(root, start, end + 1 - start, 0);
                 clear_extent_dirty(unpin, start, end, GFP_NOFS);
 
-                if (need_resched()) {
-                        mutex_unlock(&root->fs_info->pinned_mutex);
-                        cond_resched();
-                        mutex_lock(&root->fs_info->pinned_mutex);
-                }
+                cond_resched();
         }
         mutex_unlock(&root->fs_info->pinned_mutex);
         return ret;
@@ -2165,7 +2169,9 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
 
 static int pin_down_bytes(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
-                          u64 bytenr, u64 num_bytes, int is_data)
+                          struct btrfs_path *path,
+                          u64 bytenr, u64 num_bytes, int is_data,
+                          struct extent_buffer **must_clean)
 {
         int err = 0;
         struct extent_buffer *buf;
@@ -2191,15 +2197,16 @@ static int pin_down_bytes(struct btrfs_trans_handle *trans,
                     header_owner != BTRFS_DATA_RELOC_TREE_OBJECTID &&
                     header_transid == trans->transid &&
                     !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
-                        clean_tree_block(NULL, root, buf);
-                        btrfs_tree_unlock(buf);
-                        free_extent_buffer(buf);
+                        *must_clean = buf;
                         return 1;
                 }
                 btrfs_tree_unlock(buf);
         }
         free_extent_buffer(buf);
 pinit:
+        btrfs_set_path_blocking(path);
+        mutex_lock(&root->fs_info->pinned_mutex);
+        /* unlocks the pinned mutex */
         btrfs_update_pinned_extents(root, bytenr, num_bytes, 1);
 
         BUG_ON(err < 0);
@@ -2236,6 +2243,7 @@ static int __free_extent(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
 
         path->reada = 1;
+        path->leave_spinning = 1;
         ret = lookup_extent_backref(trans, extent_root, path,
                                     bytenr, parent, root_objectid,
                                     ref_generation, owner_objectid, 1);
@@ -2261,6 +2269,7 @@ static int __free_extent(struct btrfs_trans_handle *trans,
                                                     refs_to_drop);
                         BUG_ON(ret);
                         btrfs_release_path(extent_root, path);
+                        path->leave_spinning = 1;
                         ret = btrfs_search_slot(trans, extent_root,
                                                 &key, path, -1, 1);
                         if (ret) {
@@ -2318,6 +2327,7 @@ static int __free_extent(struct btrfs_trans_handle *trans,
                 /* if refs are 0, we need to setup the path for deletion */
                 if (refs == 0) {
                         btrfs_release_path(extent_root, path);
+                        path->leave_spinning = 1;
                         ret = btrfs_search_slot(trans, extent_root, &key, path,
                                                 -1, 1);
                         BUG_ON(ret);
@@ -2327,16 +2337,18 @@ static int __free_extent(struct btrfs_trans_handle *trans,
         if (refs == 0) {
                 u64 super_used;
                 u64 root_used;
+                struct extent_buffer *must_clean = NULL;
 
                 if (pin) {
-                        mutex_lock(&root->fs_info->pinned_mutex);
-                        ret = pin_down_bytes(trans, root, bytenr, num_bytes,
-                                owner_objectid >= BTRFS_FIRST_FREE_OBJECTID);
-                        mutex_unlock(&root->fs_info->pinned_mutex);
+                        ret = pin_down_bytes(trans, root, path,
+                                bytenr, num_bytes,
+                                owner_objectid >= BTRFS_FIRST_FREE_OBJECTID,
+                                &must_clean);
                         if (ret > 0)
                                 mark_free = 1;
                         BUG_ON(ret < 0);
                 }
+
                 /* block accounting for super block */
                 spin_lock(&info->delalloc_lock);
                 super_used = btrfs_super_bytes_used(&info->super_copy);
@@ -2348,11 +2360,27 @@ static int __free_extent(struct btrfs_trans_handle *trans,
                 btrfs_set_root_used(&root->root_item,
                                            root_used - num_bytes);
                 spin_unlock(&info->delalloc_lock);
+
+                /*
+                 * it is going to be very rare for someone to be waiting
+                 * on the block we're freeing.  del_items might need to
+                 * schedule, so rather than get fancy, just force it
+                 * to blocking here
+                 */
+                if (must_clean)
+                        btrfs_set_lock_blocking(must_clean);
+
                 ret = btrfs_del_items(trans, extent_root, path, path->slots[0],
                                       num_to_del);
                 BUG_ON(ret);
                 btrfs_release_path(extent_root, path);
 
+                if (must_clean) {
+                        clean_tree_block(NULL, root, must_clean);
+                        btrfs_tree_unlock(must_clean);
+                        free_extent_buffer(must_clean);
+                }
+
                 if (owner_objectid >= BTRFS_FIRST_FREE_OBJECTID) {
                         ret = btrfs_del_csums(trans, root, bytenr, num_bytes);
                         BUG_ON(ret);
@@ -2480,8 +2508,9 @@ int btrfs_free_extent(struct btrfs_trans_handle *trans,
         if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID &&
             owner_objectid < BTRFS_FIRST_FREE_OBJECTID) {
                 mutex_lock(&root->fs_info->pinned_mutex);
+
+                /* unlocks the pinned mutex */
                 btrfs_update_pinned_extents(root, bytenr, num_bytes, 1);
-                mutex_unlock(&root->fs_info->pinned_mutex);
                 update_reserved_extents(root, bytenr, num_bytes, 0);
                 ret = 0;
         } else {
@@ -2931,6 +2960,7 @@ static int __btrfs_alloc_reserved_extent(struct btrfs_trans_handle *trans,
         path = btrfs_alloc_path();
         BUG_ON(!path);
 
+        path->leave_spinning = 1;
         ret = btrfs_insert_empty_items(trans, extent_root, path, keys,
                                        sizes, 2);
         BUG_ON(ret);
@@ -5435,6 +5465,7 @@ static int __insert_orphan_inode(struct btrfs_trans_handle *trans,
         if (!path)
                 return -ENOMEM;
 
+        path->leave_spinning = 1;
         ret = btrfs_insert_empty_inode(trans, root, path, objectid);
         if (ret)
                 goto out;