ext4: refine extent status tree
This commit refines the extent status tree code.
1) A prefix 'es_' is added to to the extent status tree structure
members.
2) Refactored es_remove_extent() so that __es_remove_extent() can be
used by es_insert_extent() to remove the old extent entry(-ies) before
inserting a new one.
3) Rename extent_status_end() to ext4_es_end()
4) ext4_es_can_be_merged() is define to check whether two extents can
be merged or not.
5) Update and clarified comments.
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 564d981..c9921cf 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -23,40 +23,53 @@
* (e.g. Reservation space warning), and provide extent-level locking.
* Delay extent tree is the first step to achieve this goal. It is
* original built by Yongqiang Yang. At that time it is called delay
- * extent tree, whose goal is only track delay extent in memory to
+ * extent tree, whose goal is only track delayed extents in memory to
* simplify the implementation of fiemap and bigalloc, and introduce
* lseek SEEK_DATA/SEEK_HOLE support. That is why it is still called
- * delay extent tree at the following comment. But for better
- * understand what it does, it has been rename to extent status tree.
+ * delay extent tree at the first commit. But for better understand
+ * what it does, it has been rename to extent status tree.
*
- * Currently the first step has been done. All delay extents are
- * tracked in the tree. It maintains the delay extent when a delay
- * allocation is issued, and the delay extent is written out or
+ * Step1:
+ * Currently the first step has been done. All delayed extents are
+ * tracked in the tree. It maintains the delayed extent when a delayed
+ * allocation is issued, and the delayed extent is written out or
* invalidated. Therefore the implementation of fiemap and bigalloc
* are simplified, and SEEK_DATA/SEEK_HOLE are introduced.
*
* The following comment describes the implemenmtation of extent
* status tree and future works.
+ *
+ * Step2:
+ * In this step all extent status are tracked by extent status tree.
+ * Thus, we can first try to lookup a block mapping in this tree before
+ * finding it in extent tree. Hence, single extent cache can be removed
+ * because extent status tree can do a better job. Extents in status
+ * tree are loaded on-demand. Therefore, the extent status tree may not
+ * contain all of the extents in a file. Meanwhile we define a shrinker
+ * to reclaim memory from extent status tree because fragmented extent
+ * tree will make status tree cost too much memory. written/unwritten/-
+ * hole extents in the tree will be reclaimed by this shrinker when we
+ * are under high memory pressure. Delayed extents will not be
+ * reclimed because fiemap, bigalloc, and seek_data/hole need it.
*/
/*
- * extents status tree implementation for ext4.
+ * Extent status tree implementation for ext4.
*
*
* ==========================================================================
- * Extents status encompass delayed extents and extent locks
+ * Extent status tree tracks all extent status.
*
- * 1. Why delayed extent implementation ?
+ * 1. Why we need to implement extent status tree?
*
- * Without delayed extent, ext4 identifies a delayed extent by looking
+ * Without extent status tree, ext4 identifies a delayed extent by looking
* up page cache, this has several deficiencies - complicated, buggy,
* and inefficient code.
*
- * FIEMAP, SEEK_HOLE/DATA, bigalloc, punch hole and writeout all need
- * to know if a block or a range of blocks are belonged to a delayed
- * extent.
+ * FIEMAP, SEEK_HOLE/DATA, bigalloc, and writeout all need to know if a
+ * block or a range of blocks are belonged to a delayed extent.
*
- * Let us have a look at how they do without delayed extents implementation.
+ * Let us have a look at how they do without extent status tree.
* -- FIEMAP
* FIEMAP looks up page cache to identify delayed allocations from holes.
*
@@ -68,47 +81,48 @@
* already under delayed allocation or not to determine whether
* quota reserving is needed for the cluster.
*
- * -- punch hole
- * punch hole looks up page cache to identify a delayed extent.
- *
* -- writeout
* Writeout looks up whole page cache to see if a buffer is
* mapped, If there are not very many delayed buffers, then it is
* time comsuming.
*
- * With delayed extents implementation, FIEMAP, SEEK_HOLE/DATA,
+ * With extent status tree implementation, FIEMAP, SEEK_HOLE/DATA,
* bigalloc and writeout can figure out if a block or a range of
* blocks is under delayed allocation(belonged to a delayed extent) or
- * not by searching the delayed extent tree.
+ * not by searching the extent tree.
*
*
* ==========================================================================
- * 2. ext4 delayed extents impelmentation
+ * 2. Ext4 extent status tree impelmentation
*
- * -- delayed extent
- * A delayed extent is a range of blocks which are contiguous
- * logically and under delayed allocation. Unlike extent in
- * ext4, delayed extent in ext4 is a in-memory struct, there is
- * no corresponding on-disk data. There is no limit on length of
- * delayed extent, so a delayed extent can contain as many blocks
- * as they are contiguous logically.
+ * -- extent
+ * A extent is a range of blocks which are contiguous logically and
+ * physically. Unlike extent in extent tree, this extent in ext4 is
+ * a in-memory struct, there is no corresponding on-disk data. There
+ * is no limit on length of extent, so an extent can contain as many
+ * blocks as they are contiguous logically and physically.
*
- * -- delayed extent tree
- * Every inode has a delayed extent tree and all under delayed
- * allocation blocks are added to the tree as delayed extents.
- * Delayed extents in the tree are ordered by logical block no.
+ * -- extent status tree
+ * Every inode has an extent status tree and all allocation blocks
+ * are added to the tree with different status. The extent in the
+ * tree are ordered by logical block no.
*
- * -- operations on a delayed extent tree
- * There are three operations on a delayed extent tree: find next
- * delayed extent, adding a space(a range of blocks) and removing
- * a space.
+ * -- operations on a extent status tree
+ * There are three important operations on a delayed extent tree: find
+ * next extent, adding a extent(a range of blocks) and removing a extent.
*
- * -- race on a delayed extent tree
- * Delayed extent tree is protected inode->i_es_lock.
+ * -- race on a extent status tree
+ * Extent status tree is protected by inode->i_es_lock.
+ *
+ * -- memory consumption
+ * Fragmented extent tree will make extent status tree cost too much
+ * memory. Hence, we will reclaim written/unwritten/hole extents from
+ * the tree under a heavy memory pressure.
*
*
* ==========================================================================
- * 3. performance analysis
+ * 3. Performance analysis
+ *
* -- overhead
* 1. There is a cache extent for write access, so if writes are
* not very random, adding space operaions are in O(1) time.
@@ -120,15 +134,19 @@
*
* ==========================================================================
* 4. TODO list
- * -- Track all extent status
*
- * -- Improve get block process
+ * -- Refactor delayed space reservation
*
* -- Extent-level locking
*/
static struct kmem_cache *ext4_es_cachep;
+static int __es_insert_extent(struct ext4_es_tree *tree,
+ struct extent_status *newes);
+static int __es_remove_extent(struct ext4_es_tree *tree, ext4_lblk_t lblk,
+ ext4_lblk_t end);
+
int __init ext4_init_es(void)
{
ext4_es_cachep = KMEM_CACHE(extent_status, SLAB_RECLAIM_ACCOUNT);
@@ -161,7 +179,7 @@
while (node) {
struct extent_status *es;
es = rb_entry(node, struct extent_status, rb_node);
- printk(KERN_DEBUG " [%u/%u)", es->start, es->len);
+ printk(KERN_DEBUG " [%u/%u)", es->es_lblk, es->es_len);
node = rb_next(node);
}
printk(KERN_DEBUG "\n");
@@ -170,10 +188,10 @@
#define ext4_es_print_tree(inode)
#endif
-static inline ext4_lblk_t extent_status_end(struct extent_status *es)
+static inline ext4_lblk_t ext4_es_end(struct extent_status *es)
{
- BUG_ON(es->start + es->len < es->start);
- return es->start + es->len - 1;
+ BUG_ON(es->es_lblk + es->es_len < es->es_lblk);
+ return es->es_lblk + es->es_len - 1;
}
/*
@@ -181,25 +199,25 @@
* it can't be found, try to find next extent.
*/
static struct extent_status *__es_tree_search(struct rb_root *root,
- ext4_lblk_t offset)
+ ext4_lblk_t lblk)
{
struct rb_node *node = root->rb_node;
struct extent_status *es = NULL;
while (node) {
es = rb_entry(node, struct extent_status, rb_node);
- if (offset < es->start)
+ if (lblk < es->es_lblk)
node = node->rb_left;
- else if (offset > extent_status_end(es))
+ else if (lblk > ext4_es_end(es))
node = node->rb_right;
else
return es;
}
- if (es && offset < es->start)
+ if (es && lblk < es->es_lblk)
return es;
- if (es && offset > extent_status_end(es)) {
+ if (es && lblk > ext4_es_end(es)) {
node = rb_next(&es->rb_node);
return node ? rb_entry(node, struct extent_status, rb_node) :
NULL;
@@ -209,8 +227,8 @@
}
/*
- * ext4_es_find_extent: find the 1st delayed extent covering @es->start
- * if it exists, otherwise, the next extent after @es->start.
+ * ext4_es_find_extent: find the 1st delayed extent covering @es->lblk
+ * if it exists, otherwise, the next extent after @es->lblk.
*
* @inode: the inode which owns delayed extents
* @es: delayed extent that we found
@@ -226,7 +244,7 @@
struct rb_node *node;
ext4_lblk_t ret = EXT_MAX_BLOCKS;
- trace_ext4_es_find_extent_enter(inode, es->start);
+ trace_ext4_es_find_extent_enter(inode, es->es_lblk);
read_lock(&EXT4_I(inode)->i_es_lock);
tree = &EXT4_I(inode)->i_es_tree;
@@ -234,25 +252,25 @@
/* find delay extent in cache firstly */
if (tree->cache_es) {
es1 = tree->cache_es;
- if (in_range(es->start, es1->start, es1->len)) {
+ if (in_range(es->es_lblk, es1->es_lblk, es1->es_len)) {
es_debug("%u cached by [%u/%u)\n",
- es->start, es1->start, es1->len);
+ es->es_lblk, es1->es_lblk, es1->es_len);
goto out;
}
}
- es->len = 0;
- es1 = __es_tree_search(&tree->root, es->start);
+ es->es_len = 0;
+ es1 = __es_tree_search(&tree->root, es->es_lblk);
out:
if (es1) {
tree->cache_es = es1;
- es->start = es1->start;
- es->len = es1->len;
+ es->es_lblk = es1->es_lblk;
+ es->es_len = es1->es_len;
node = rb_next(&es1->rb_node);
if (node) {
es1 = rb_entry(node, struct extent_status, rb_node);
- ret = es1->start;
+ ret = es1->es_lblk;
}
}
@@ -263,14 +281,14 @@
}
static struct extent_status *
-ext4_es_alloc_extent(ext4_lblk_t start, ext4_lblk_t len)
+ext4_es_alloc_extent(ext4_lblk_t lblk, ext4_lblk_t len)
{
struct extent_status *es;
es = kmem_cache_alloc(ext4_es_cachep, GFP_ATOMIC);
if (es == NULL)
return NULL;
- es->start = start;
- es->len = len;
+ es->es_lblk = lblk;
+ es->es_len = len;
return es;
}
@@ -279,6 +297,20 @@
kmem_cache_free(ext4_es_cachep, es);
}
+/*
+ * Check whether or not two extents can be merged
+ * Condition:
+ * - logical block number is contiguous
+ */
+static int ext4_es_can_be_merged(struct extent_status *es1,
+ struct extent_status *es2)
+{
+ if (es1->es_lblk + es1->es_len != es2->es_lblk)
+ return 0;
+
+ return 1;
+}
+
static struct extent_status *
ext4_es_try_to_merge_left(struct ext4_es_tree *tree, struct extent_status *es)
{
@@ -290,8 +322,8 @@
return es;
es1 = rb_entry(node, struct extent_status, rb_node);
- if (es->start == extent_status_end(es1) + 1) {
- es1->len += es->len;
+ if (ext4_es_can_be_merged(es1, es)) {
+ es1->es_len += es->es_len;
rb_erase(&es->rb_node, &tree->root);
ext4_es_free_extent(es);
es = es1;
@@ -311,8 +343,8 @@
return es;
es1 = rb_entry(node, struct extent_status, rb_node);
- if (es1->start == extent_status_end(es) + 1) {
- es->len += es1->len;
+ if (ext4_es_can_be_merged(es, es1)) {
+ es->es_len += es1->es_len;
rb_erase(node, &tree->root);
ext4_es_free_extent(es1);
}
@@ -320,60 +352,43 @@
return es;
}
-static int __es_insert_extent(struct ext4_es_tree *tree, ext4_lblk_t offset,
- ext4_lblk_t len)
+static int __es_insert_extent(struct ext4_es_tree *tree,
+ struct extent_status *newes)
{
struct rb_node **p = &tree->root.rb_node;
struct rb_node *parent = NULL;
struct extent_status *es;
- ext4_lblk_t end = offset + len - 1;
-
- BUG_ON(end < offset);
- es = tree->cache_es;
- if (es && offset == (extent_status_end(es) + 1)) {
- es_debug("cached by [%u/%u)\n", es->start, es->len);
- es->len += len;
- es = ext4_es_try_to_merge_right(tree, es);
- goto out;
- } else if (es && es->start == end + 1) {
- es_debug("cached by [%u/%u)\n", es->start, es->len);
- es->start = offset;
- es->len += len;
- es = ext4_es_try_to_merge_left(tree, es);
- goto out;
- } else if (es && es->start <= offset &&
- end <= extent_status_end(es)) {
- es_debug("cached by [%u/%u)\n", es->start, es->len);
- goto out;
- }
while (*p) {
parent = *p;
es = rb_entry(parent, struct extent_status, rb_node);
- if (offset < es->start) {
- if (es->start == end + 1) {
- es->start = offset;
- es->len += len;
+ if (newes->es_lblk < es->es_lblk) {
+ if (ext4_es_can_be_merged(newes, es)) {
+ /*
+ * Here we can modify es_lblk directly
+ * because it isn't overlapped.
+ */
+ es->es_lblk = newes->es_lblk;
+ es->es_len += newes->es_len;
es = ext4_es_try_to_merge_left(tree, es);
goto out;
}
p = &(*p)->rb_left;
- } else if (offset > extent_status_end(es)) {
- if (offset == extent_status_end(es) + 1) {
- es->len += len;
+ } else if (newes->es_lblk > ext4_es_end(es)) {
+ if (ext4_es_can_be_merged(es, newes)) {
+ es->es_len += newes->es_len;
es = ext4_es_try_to_merge_right(tree, es);
goto out;
}
p = &(*p)->rb_right;
} else {
- if (extent_status_end(es) <= end)
- es->len = offset - es->start + len;
- goto out;
+ BUG_ON(1);
+ return -EINVAL;
}
}
- es = ext4_es_alloc_extent(offset, len);
+ es = ext4_es_alloc_extent(newes->es_lblk, newes->es_len);
if (!es)
return -ENOMEM;
rb_link_node(&es->rb_node, parent, p);
@@ -385,27 +400,38 @@
}
/*
- * ext4_es_insert_extent() adds a space to a delayed extent tree.
- * Caller holds inode->i_es_lock.
+ * ext4_es_insert_extent() adds a space to a extent status tree.
*
* ext4_es_insert_extent is called by ext4_da_write_begin and
* ext4_es_remove_extent.
*
* Return 0 on success, error code on failure.
*/
-int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t offset,
+int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
ext4_lblk_t len)
{
struct ext4_es_tree *tree;
+ struct extent_status newes;
+ ext4_lblk_t end = lblk + len - 1;
int err = 0;
- trace_ext4_es_insert_extent(inode, offset, len);
+ trace_ext4_es_insert_extent(inode, lblk, len);
es_debug("add [%u/%u) to extent status tree of inode %lu\n",
- offset, len, inode->i_ino);
+ lblk, len, inode->i_ino);
+
+ BUG_ON(end < lblk);
+
+ newes.es_lblk = lblk;
+ newes.es_len = len;
write_lock(&EXT4_I(inode)->i_es_lock);
tree = &EXT4_I(inode)->i_es_tree;
- err = __es_insert_extent(tree, offset, len);
+ err = __es_remove_extent(tree, lblk, end);
+ if (err != 0)
+ goto error;
+ err = __es_insert_extent(tree, &newes);
+
+error:
write_unlock(&EXT4_I(inode)->i_es_lock);
ext4_es_print_tree(inode);
@@ -413,57 +439,45 @@
return err;
}
-/*
- * ext4_es_remove_extent() removes a space from a delayed extent tree.
- * Caller holds inode->i_es_lock.
- *
- * Return 0 on success, error code on failure.
- */
-int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t offset,
- ext4_lblk_t len)
+static int __es_remove_extent(struct ext4_es_tree *tree, ext4_lblk_t lblk,
+ ext4_lblk_t end)
{
struct rb_node *node;
- struct ext4_es_tree *tree;
struct extent_status *es;
struct extent_status orig_es;
- ext4_lblk_t len1, len2, end;
+ ext4_lblk_t len1, len2;
int err = 0;
- trace_ext4_es_remove_extent(inode, offset, len);
- es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
- offset, len, inode->i_ino);
-
- end = offset + len - 1;
- BUG_ON(end < offset);
- write_lock(&EXT4_I(inode)->i_es_lock);
- tree = &EXT4_I(inode)->i_es_tree;
- es = __es_tree_search(&tree->root, offset);
+ es = __es_tree_search(&tree->root, lblk);
if (!es)
goto out;
- if (es->start > end)
+ if (es->es_lblk > end)
goto out;
/* Simply invalidate cache_es. */
tree->cache_es = NULL;
- orig_es.start = es->start;
- orig_es.len = es->len;
- len1 = offset > es->start ? offset - es->start : 0;
- len2 = extent_status_end(es) > end ?
- extent_status_end(es) - end : 0;
+ orig_es.es_lblk = es->es_lblk;
+ orig_es.es_len = es->es_len;
+ len1 = lblk > es->es_lblk ? lblk - es->es_lblk : 0;
+ len2 = ext4_es_end(es) > end ? ext4_es_end(es) - end : 0;
if (len1 > 0)
- es->len = len1;
+ es->es_len = len1;
if (len2 > 0) {
if (len1 > 0) {
- err = __es_insert_extent(tree, end + 1, len2);
+ struct extent_status newes;
+
+ newes.es_lblk = end + 1;
+ newes.es_len = len2;
+ err = __es_insert_extent(tree, &newes);
if (err) {
- es->start = orig_es.start;
- es->len = orig_es.len;
+ es->es_lblk = orig_es.es_lblk;
+ es->es_len = orig_es.es_len;
goto out;
}
} else {
- es->start = end + 1;
- es->len = len2;
+ es->es_lblk = end + 1;
+ es->es_len = len2;
}
goto out;
}
@@ -476,7 +490,7 @@
es = NULL;
}
- while (es && extent_status_end(es) <= end) {
+ while (es && ext4_es_end(es) <= end) {
node = rb_next(&es->rb_node);
rb_erase(&es->rb_node, &tree->root);
ext4_es_free_extent(es);
@@ -487,13 +501,39 @@
es = rb_entry(node, struct extent_status, rb_node);
}
- if (es && es->start < end + 1) {
- len1 = extent_status_end(es) - end;
- es->start = end + 1;
- es->len = len1;
+ if (es && es->es_lblk < end + 1) {
+ len1 = ext4_es_end(es) - end;
+ es->es_lblk = end + 1;
+ es->es_len = len1;
}
out:
+ return err;
+}
+
+/*
+ * ext4_es_remove_extent() removes a space from a extent status tree.
+ *
+ * Return 0 on success, error code on failure.
+ */
+int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
+ ext4_lblk_t len)
+{
+ struct ext4_es_tree *tree;
+ ext4_lblk_t end;
+ int err = 0;
+
+ trace_ext4_es_remove_extent(inode, lblk, len);
+ es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
+ lblk, len, inode->i_ino);
+
+ end = lblk + len - 1;
+ BUG_ON(end < lblk);
+
+ tree = &EXT4_I(inode)->i_es_tree;
+
+ write_lock(&EXT4_I(inode)->i_es_lock);
+ err = __es_remove_extent(tree, lblk, end);
write_unlock(&EXT4_I(inode)->i_es_lock);
ext4_es_print_tree(inode);
return err;