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authorLiu Bo <bo.liu@linux.alibaba.com>2018-08-23 03:51:49 +0800
committerDavid Sterba <dsterba@suse.com>2018-10-15 17:23:33 +0200
commit5c9d028b3b174e5cf3678a7b0c14e21e51665793 (patch)
tree7871db45680d3cb98c67dc8ee31a8e5a8275abcf /fs/btrfs/delayed-ref.h
parent3aa7c7a31c26321696b92841d5103461c6f3f517 (diff)
Btrfs: delayed-refs: use rb_first_cached for href_root
rb_first_cached() trades an extra pointer "leftmost" for doing the same job as rb_first() but in O(1). Functions manipulating href_root need to get the first entry, this converts href_root to use rb_first_cached(). This patch is first in the sequenct of similar updates to other rbtrees and this is analysis of the expected behaviour and improvements. There's a common pattern: while (node = rb_first) { entry = rb_entry(node) next = rb_next(node) rb_erase(node) cleanup(entry) } rb_first needs to traverse the tree up to logN depth, rb_erase can completely reshuffle the tree. With the caching we'll skip the traversal in rb_first. That's a cached memory access vs looped pointer dereference trade-off that IMHO has a clear winner. Measurements show there's not much difference in a sample tree with 10000 nodes: 4.5s / rb_first and 4.8s / rb_first_cached. Real effects of caching and pointer chasing are unpredictable though. Further optimzations can be done to avoid the expensive rb_erase step. In some cases it's ok to process the nodes in any order, so the tree can be traversed in post-order, not rebalancing the children nodes and just calling free. Care must be taken regarding the next node. Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com> Reviewed-by: David Sterba <dsterba@suse.com> [ update changelog from mail discussions ] Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/delayed-ref.h')
-rw-r--r--fs/btrfs/delayed-ref.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index d9f2a4ebd5db..88438b6cee45 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -148,7 +148,7 @@ struct btrfs_delayed_data_ref {
struct btrfs_delayed_ref_root {
/* head ref rbtree */
- struct rb_root href_root;
+ struct rb_root_cached href_root;
/* dirty extent records */
struct rb_root dirty_extent_root;