On Wed, Apr 21, 2010 at 09:48:17AM +0800, Shaohua Li wrote: > On Tue, Apr 20, 2010 at 10:39:01PM +0800, Josef Bacik wrote: > > On Tue, Apr 20, 2010 at 05:21:58PM +0800, Shaohua Li wrote: > > > searching extent_io_tree is frequently used and tooks a lot of cpu time. > > > We could cache last found extent_state to skip some full search. In my > > > test, the hit rate is from 30% to 70% depending on different workload, > > > which can speed up the search. > > > > > > Signed-off-by: Shaohua Li <[email protected]> > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > index d2d0368..645f00c 100644 > > > --- a/fs/btrfs/extent_io.c > > > +++ b/fs/btrfs/extent_io.c > > > @@ -110,6 +110,7 @@ void extent_io_tree_init(struct extent_io_tree *tree, > > > spin_lock_init(&tree->lock); > > > spin_lock_init(&tree->buffer_lock); > > > tree->mapping = mapping; > > > + tree->cached_state = NULL; > > > } > > > > > > static struct extent_state *alloc_extent_state(gfp_t mask) > > > @@ -135,6 +136,22 @@ static struct extent_state *alloc_extent_state(gfp_t > > > mask) > > > return state; > > > } > > > > > > +static void remove_cached_extent(struct extent_io_tree *tree, > > > + struct extent_state *state) > > > +{ > > > + if (!tree->cached_state) > > > + return; > > > + if (tree->cached_state == state) > > > + tree->cached_state = NULL; > > > +} > > > + > > > +static void merge_cached_extent(struct extent_io_tree *tree, > > > + struct extent_state *first, struct extent_state *last) > > > +{ > > > + if (tree->cached_state == first || tree->cached_state == last) > > > + tree->cached_state = first; > > > +} > > > + > > > static void free_extent_state(struct extent_state *state) > > > { > > > if (!state) > > > @@ -188,6 +205,12 @@ static struct rb_node *__etree_search(struct > > > extent_io_tree *tree, u64 offset, > > > struct rb_node *orig_prev = NULL; > > > struct tree_entry *entry; > > > struct tree_entry *prev_entry = NULL; > > > + struct tree_entry *cached_entry = > > > + (struct tree_entry *)tree->cached_state; > > > + > > > + if (likely(cached_entry && offset >= cached_entry->start && > > > + offset <= cached_entry->end)) > > > + return &cached_entry->rb_node; > > > > > > while (n) { > > > entry = rb_entry(n, struct tree_entry, rb_node); > > > @@ -198,8 +221,10 @@ static struct rb_node *__etree_search(struct > > > extent_io_tree *tree, u64 offset, > > > n = n->rb_left; > > > else if (offset > entry->end) > > > n = n->rb_right; > > > - else > > > + else { > > > + tree->cached_state = (struct extent_state *)entry; > > > return n; > > > + } > > > } > > > > > > if (prev_ret) { > > > @@ -313,6 +338,7 @@ static int merge_state(struct extent_io_tree *tree, > > > merge_cb(tree, state, other); > > > state->start = other->start; > > > other->tree = NULL; > > > + merge_cached_extent(tree, state, other); > > > rb_erase(&other->rb_node, &tree->state); > > > free_extent_state(other); > > > } > > > @@ -325,6 +351,7 @@ static int merge_state(struct extent_io_tree *tree, > > > merge_cb(tree, state, other); > > > other->start = state->start; > > > state->tree = NULL; > > > + merge_cached_extent(tree, other, state); > > > rb_erase(&state->rb_node, &tree->state); > > > free_extent_state(state); > > > state = NULL; > > > @@ -473,6 +500,7 @@ static int clear_state_bit(struct extent_io_tree > > > *tree, > > > wake_up(&state->wq); > > > if (delete || state->state == 0) { > > > if (state->tree) { > > > + remove_cached_extent(tree, state); > > > clear_state_cb(tree, state, state->state); > > > rb_erase(&state->rb_node, &tree->state); > > > state->tree = NULL; > > > diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h > > > index bbab481..e60b367 100644 > > > --- a/fs/btrfs/extent_io.h > > > +++ b/fs/btrfs/extent_io.h > > > @@ -89,6 +89,7 @@ struct extent_io_tree { > > > spinlock_t lock; > > > spinlock_t buffer_lock; > > > struct extent_io_ops *ops; > > > + struct extent_state *cached_state; > > > }; > > > > > > struct extent_state { > > > > Sorry I saw this earlier but then forgot about it. So instead of doing a > > per-tree thing, which will end up with misses if somebody else tries to > > search > > the tree for a different offset, you will want to do something like this > > > > http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-unstable.git;a=commit;h=2ac55d41b5d6bf49e76bc85db5431240617e2f8f > > > > So that way _anybody_ who does a search will have a cached state, and so all > > subsequent searches won't be needed, instead of only working for the first > > guy > > who gets their state cached. Thanks, > Hmm, the patch you pointed out is already in upstream but I still saw the > search > takes a lot of CPU. >
I've probably missed some places where we could be using cached extent states, I wasn't terribly thorough when I was checking. It may be good to instrument the cases where we come into test/clear/set bits and we not end up using the cached state to see where the trouble spots are. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
