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f2fs: support fast lookup in extent cache

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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>
This commit is contained in:
Chao Yu 2015-02-05 18:01:39 +08:00 committed by Jaegeuk Kim
parent 1ec4610c52
commit 62c8af651b
2 changed files with 17 additions and 3 deletions
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19
fs/f2fs/data.c
View File

@ -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;

1
fs/f2fs/f2fs.h
View File

@ -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*/