f2fs: support fast lookup in extent cache

This patch adds a fast lookup path for rb-tree extent cache.

In this patch we add a recently accessed extent node pointer 'cached_en' in
extent tree. In lookup path of extent cache, we will firstly lookup the last
accessed extent node which cached_en points, if we do not hit in this node,
we will try to lookup extent node in rb-tree.

By this way we can avoid unnecessary slow lookup in rb-tree sometimes.

Note that, side-effect of this patch is that we will increase memory cost,
because we will store a pointer variable in each struct extent tree
additionally.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index d7ff4ca5be185825e9aea2c7f95d595c02460ac1..08a71ae3ab8d1c8b8cb71429183c580f333f135e 100644 (file)
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -395,6 +395,9 @@ static void __detach_extent_node(struct f2fs_sb_info *sbi,
        rb_erase(&en->rb_node, &et->root);
        et->count--;
        atomic_dec(&sbi->total_ext_node);
+
+       if (et->cached_en == en)
+               et->cached_en = NULL;
 }
 
 static struct extent_node *__lookup_extent_tree(struct extent_tree *et,
@@ -403,15 +406,24 @@ static struct extent_node *__lookup_extent_tree(struct extent_tree *et,
        struct rb_node *node = et->root.rb_node;
        struct extent_node *en;
 
+       if (et->cached_en) {
+               struct extent_info *cei = &et->cached_en->ei;
+
+               if (cei->fofs <= fofs && cei->fofs + cei->len > fofs)
+                       return et->cached_en;
+       }
+
        while (node) {
                en = rb_entry(node, struct extent_node, rb_node);
 
-               if (fofs < en->ei.fofs)
+               if (fofs < en->ei.fofs) {
                        node = node->rb_left;
-               else if (fofs >= en->ei.fofs + en->ei.len)
+               } else if (fofs >= en->ei.fofs + en->ei.len) {
                        node = node->rb_right;
-               else
+               } else {
+                       et->cached_en = en;
                        return en;
+               }
        }
        return NULL;
 }
@@ -587,6 +599,7 @@ static void f2fs_update_extent_tree(struct inode *inode, pgoff_t fofs,
                memset(et, 0, sizeof(struct extent_tree));
                et->ino = ino;
                et->root = RB_ROOT;
+               et->cached_en = NULL;
                rwlock_init(&et->lock);
                atomic_set(&et->refcount, 0);
                et->count = 0;

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 85ce9b30b539266a2bf9eb4b2133b10eaa776897..08fc7e0d5e4ab9496286e31a5d42e46385005047 100644 (file)
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -298,6 +298,7 @@ struct extent_node {
 struct extent_tree {
        nid_t ino;                      /* inode number */
        struct rb_root root;            /* root of extent info rb-tree */
+       struct extent_node *cached_en;  /* recently accessed extent node */
        rwlock_t lock;                  /* protect extent info rb-tree */
        atomic_t refcount;              /* reference count of rb-tree */
        unsigned int count;             /* # of extent node in rb-tree*/