On Fri 08-02-13 16:44:00, Zheng Liu wrote:
> From: Zheng Liu <wenqing.lz@xxxxxxxxxx>
>
> By recording the phycisal block and status, extent status tree is able
> to track the status of every extents. When we call _map_blocks
> functions to lookup an extent or create a new written/unwritten/delayed
> extent, this extent will be inserted into extent status tree. The hole
> extent is inserted in ext4_ext_put_gap_in_cache(). If there is no any
> extent, we will not insert a hole extent [0, ~0] into the extent status
> tree in order to reduce the complextiy of code.
>
> We don't load all extents from disk in alloc_inode() because it costs
> too much memory, and if a file is opened and closed frequently it will
> takes too much time to load all extent information. So currently when
> we create/lookup an extent, this extent will be inserted into extent
> status tree. Hence, the extent status tree may not comprehensively
> contain all of the extents found in the file.
>
> Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Jan kara <jack@xxxxxxx>
> ---
> fs/ext4/extents.c | 4 +--
> fs/ext4/extents_status.c | 27 ++++++++++++------
> fs/ext4/extents_status.h | 4 +--
> fs/ext4/file.c | 4 +--
> fs/ext4/inode.c | 68 ++++++++++++++++++++++++++++-----------------
> include/trace/events/ext4.h | 4 +--
> 6 files changed, 70 insertions(+), 41 deletions(-)
>
...
> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
> index 5093cee..71cb75a 100644
> --- a/fs/ext4/extents_status.c
> +++ b/fs/ext4/extents_status.c
> @@ -239,14 +239,15 @@ static struct extent_status *__es_tree_search(struct rb_root *root,
> * EXT_MAX_BLOCKS if no extent is found.
> * Delayed extent is returned via @es.
> */
> -ext4_lblk_t ext4_es_find_extent(struct inode *inode, struct extent_status *es)
> +ext4_lblk_t ext4_es_find_delayed_extent(struct inode *inode,
> + struct extent_status *es)
> {
I have to say I'm still not very happy about this function (but it's much
better than it used to be so thanks for that!). I have two suggestions for
improvement:
1) 'es' is both input and output argument where for input only es_lblk is
used. That's a bit confusing so how about making the function like:
ext4_es_find_delayed_extent(struct inode *inode, ext4_lblk_t offset,
struct extent_status *out);
to separate input and output? Also you can comment that we use the 'out'
parameter instead of returning the extent_status from the tree because that
can be freed once we drop the spinlock protecting status tree.
2) The returned value is somewhat surprisingly the logical offset of the
*next* delalloc extent. It's used only in ext4_fill_fiemap_extents()
AFAICS. It would be easier to understand if the function didn't return
anything. ext4_fill_fiemap_extents() would use
ext4_es_find_delayed_extent() to find both current and next delalloc extent
(which would become the 'current' one in the next iteration). As a bonus
you would also save some iteration of the extent status tree...
> struct ext4_es_tree *tree = NULL;
> struct extent_status *es1 = NULL;
> struct rb_node *node;
> ext4_lblk_t ret = EXT_MAX_BLOCKS;
>
> - trace_ext4_es_find_extent_enter(inode, es->es_lblk);
> + trace_ext4_es_find_delayed_extent_enter(inode, es->es_lblk);
>
> read_lock(&EXT4_I(inode)->i_es_lock);
> tree = &EXT4_I(inode)->i_es_tree;
> @@ -266,21 +267,31 @@ ext4_lblk_t ext4_es_find_extent(struct inode *inode, struct extent_status *es)
> es1 = __es_tree_search(&tree->root, es->es_lblk);
>
> out:
> - if (es1) {
> + if (es1 && !ext4_es_is_delayed(es1)) {
> + while ((node = rb_next(&es1->rb_node)) != NULL) {
> + es1 = rb_entry(node, struct extent_status, rb_node);
> + if (ext4_es_is_delayed(es1))
> + break;
> + }
> + }
> +
> + if (es1 && ext4_es_is_delayed(es1)) {
> tree->cache_es = es1;
> es->es_lblk = es1->es_lblk;
> es->es_len = es1->es_len;
> es->es_pblk = es1->es_pblk;
> - node = rb_next(&es1->rb_node);
> - if (node) {
> + while ((node = rb_next(&es1->rb_node)) != NULL) {
> es1 = rb_entry(node, struct extent_status, rb_node);
> - ret = es1->es_lblk;
> + if (ext4_es_is_delayed(es1)) {
> + ret = es1->es_lblk;
> + break;
> + }
> }
> }
>
> read_unlock(&EXT4_I(inode)->i_es_lock);
>
> - trace_ext4_es_find_extent_exit(inode, es, ret);
> + trace_ext4_es_find_delayed_extent_exit(inode, es, ret);
> return ret;
> }
>
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
