ext4: add operations on extent status tree
This patch adds operations on a extent status tree.
CC: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: Allison Henderson <achender@linux.vnet.ibm.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
new file mode 100644
index 0000000..02c09be
--- /dev/null
+++ b/fs/ext4/extents_status.c
@@ -0,0 +1,492 @@
+/*
+ * fs/ext4/extents_status.c
+ *
+ * Written by Yongqiang Yang <xiaoqiangnk@gmail.com>
+ * Modified by
+ * Allison Henderson <achender@linux.vnet.ibm.com>
+ * Hugh Dickins <hughd@google.com>
+ * Zheng Liu <wenqing.lz@taobao.com>
+ *
+ * Ext4 extents status tree core functions.
+ */
+#include <linux/rbtree.h>
+#include "ext4.h"
+#include "extents_status.h"
+#include "ext4_extents.h"
+
+/*
+ * According to previous discussion in Ext4 Developer Workshop, we
+ * will introduce a new structure called io tree to track all extent
+ * status in order to solve some problems that we have met
+ * (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
+ * 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.
+ *
+ * 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
+ * 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.
+ */
+
+/*
+ * extents status tree implementation for ext4.
+ *
+ *
+ * ==========================================================================
+ * Extents status encompass delayed extents and extent locks
+ *
+ * 1. Why delayed extent implementation ?
+ *
+ * Without delayed extent, 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.
+ *
+ * Let us have a look at how they do without delayed extents implementation.
+ * -- FIEMAP
+ * FIEMAP looks up page cache to identify delayed allocations from holes.
+ *
+ * -- SEEK_HOLE/DATA
+ * SEEK_HOLE/DATA has the same problem as FIEMAP.
+ *
+ * -- bigalloc
+ * bigalloc looks up page cache to figure out if a block is
+ * 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,
+ * 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.
+ *
+ *
+ * ==========================================================================
+ * 2. ext4 delayed extents 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.
+ *
+ * -- 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.
+ *
+ * -- 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.
+ *
+ * -- race on a delayed extent tree
+ * Delayed extent tree is protected inode->i_es_lock.
+ *
+ *
+ * ==========================================================================
+ * 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.
+ *
+ * -- gain
+ * 2. Code is much simpler, more readable, more maintainable and
+ * more efficient.
+ *
+ *
+ * ==========================================================================
+ * 4. TODO list
+ * -- Track all extent status
+ *
+ * -- Improve get block process
+ *
+ * -- Extent-level locking
+ */
+
+static struct kmem_cache *ext4_es_cachep;
+
+int __init ext4_init_es(void)
+{
+ ext4_es_cachep = KMEM_CACHE(extent_status, SLAB_RECLAIM_ACCOUNT);
+ if (ext4_es_cachep == NULL)
+ return -ENOMEM;
+ return 0;
+}
+
+void ext4_exit_es(void)
+{
+ if (ext4_es_cachep)
+ kmem_cache_destroy(ext4_es_cachep);
+}
+
+void ext4_es_init_tree(struct ext4_es_tree *tree)
+{
+ tree->root = RB_ROOT;
+ tree->cache_es = NULL;
+}
+
+#ifdef ES_DEBUG__
+static void ext4_es_print_tree(struct inode *inode)
+{
+ struct ext4_es_tree *tree;
+ struct rb_node *node;
+
+ printk(KERN_DEBUG "status extents for inode %lu:", inode->i_ino);
+ tree = &EXT4_I(inode)->i_es_tree;
+ node = rb_first(&tree->root);
+ while (node) {
+ struct extent_status *es;
+ es = rb_entry(node, struct extent_status, rb_node);
+ printk(KERN_DEBUG " [%u/%u)", es->start, es->len);
+ node = rb_next(node);
+ }
+ printk(KERN_DEBUG "\n");
+}
+#else
+#define ext4_es_print_tree(inode)
+#endif
+
+static inline ext4_lblk_t extent_status_end(struct extent_status *es)
+{
+ BUG_ON(es->start + es->len < es->start);
+ return es->start + es->len - 1;
+}
+
+/*
+ * search through the tree for an delayed extent with a given offset. If
+ * 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)
+{
+ 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)
+ node = node->rb_left;
+ else if (offset > extent_status_end(es))
+ node = node->rb_right;
+ else
+ return es;
+ }
+
+ if (es && offset < es->start)
+ return es;
+
+ if (es && offset > extent_status_end(es)) {
+ node = rb_next(&es->rb_node);
+ return node ? rb_entry(node, struct extent_status, rb_node) :
+ NULL;
+ }
+
+ return NULL;
+}
+
+/*
+ * ext4_es_find_extent: find the 1st delayed extent covering @es->start
+ * if it exists, otherwise, the next extent after @es->start.
+ *
+ * @inode: the inode which owns delayed extents
+ * @es: delayed extent that we found
+ *
+ * Returns the first block of the next extent after es, otherwise
+ * EXT_MAX_BLOCKS if no delay extent is found.
+ * Delayed extent is returned via @es.
+ */
+ext4_lblk_t ext4_es_find_extent(struct inode *inode, struct extent_status *es)
+{
+ struct ext4_es_tree *tree = NULL;
+ struct extent_status *es1 = NULL;
+ struct rb_node *node;
+ ext4_lblk_t ret = EXT_MAX_BLOCKS;
+
+ read_lock(&EXT4_I(inode)->i_es_lock);
+ tree = &EXT4_I(inode)->i_es_tree;
+
+ /* find delay extent in cache firstly */
+ if (tree->cache_es) {
+ es1 = tree->cache_es;
+ if (in_range(es->start, es1->start, es1->len)) {
+ es_debug("%u cached by [%u/%u)\n",
+ es->start, es1->start, es1->len);
+ goto out;
+ }
+ }
+
+ es->len = 0;
+ es1 = __es_tree_search(&tree->root, es->start);
+
+out:
+ if (es1) {
+ tree->cache_es = es1;
+ es->start = es1->start;
+ es->len = es1->len;
+ node = rb_next(&es1->rb_node);
+ if (node) {
+ es1 = rb_entry(node, struct extent_status, rb_node);
+ ret = es1->start;
+ }
+ }
+
+ read_unlock(&EXT4_I(inode)->i_es_lock);
+ return ret;
+}
+
+static struct extent_status *
+ext4_es_alloc_extent(ext4_lblk_t start, 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;
+ return es;
+}
+
+static void ext4_es_free_extent(struct extent_status *es)
+{
+ kmem_cache_free(ext4_es_cachep, es);
+}
+
+static struct extent_status *
+ext4_es_try_to_merge_left(struct ext4_es_tree *tree, struct extent_status *es)
+{
+ struct extent_status *es1;
+ struct rb_node *node;
+
+ node = rb_prev(&es->rb_node);
+ if (!node)
+ return es;
+
+ es1 = rb_entry(node, struct extent_status, rb_node);
+ if (es->start == extent_status_end(es1) + 1) {
+ es1->len += es->len;
+ rb_erase(&es->rb_node, &tree->root);
+ ext4_es_free_extent(es);
+ es = es1;
+ }
+
+ return es;
+}
+
+static struct extent_status *
+ext4_es_try_to_merge_right(struct ext4_es_tree *tree, struct extent_status *es)
+{
+ struct extent_status *es1;
+ struct rb_node *node;
+
+ node = rb_next(&es->rb_node);
+ if (!node)
+ return es;
+
+ es1 = rb_entry(node, struct extent_status, rb_node);
+ if (es1->start == extent_status_end(es) + 1) {
+ es->len += es1->len;
+ rb_erase(node, &tree->root);
+ ext4_es_free_extent(es1);
+ }
+
+ return es;
+}
+
+static int __es_insert_extent(struct ext4_es_tree *tree, ext4_lblk_t offset,
+ ext4_lblk_t len)
+{
+ 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;
+ 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;
+ 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;
+ }
+ }
+
+ es = ext4_es_alloc_extent(offset, len);
+ if (!es)
+ return -ENOMEM;
+ rb_link_node(&es->rb_node, parent, p);
+ rb_insert_color(&es->rb_node, &tree->root);
+
+out:
+ tree->cache_es = es;
+ return 0;
+}
+
+/*
+ * ext4_es_insert_extent() adds a space to a delayed extent tree.
+ * Caller holds inode->i_es_lock.
+ *
+ * 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,
+ ext4_lblk_t len)
+{
+ struct ext4_es_tree *tree;
+ int err = 0;
+
+ es_debug("add [%u/%u) to extent status tree of inode %lu\n",
+ offset, len, inode->i_ino);
+
+ write_lock(&EXT4_I(inode)->i_es_lock);
+ tree = &EXT4_I(inode)->i_es_tree;
+ err = __es_insert_extent(tree, offset, len);
+ write_unlock(&EXT4_I(inode)->i_es_lock);
+
+ ext4_es_print_tree(inode);
+
+ 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)
+{
+ struct rb_node *node;
+ struct ext4_es_tree *tree;
+ struct extent_status *es;
+ struct extent_status orig_es;
+ ext4_lblk_t len1, len2, end;
+ int err = 0;
+
+ 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);
+ if (!es)
+ goto out;
+ if (es->start > 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;
+ if (len1 > 0)
+ es->len = len1;
+ if (len2 > 0) {
+ if (len1 > 0) {
+ err = __es_insert_extent(tree, end + 1, len2);
+ if (err) {
+ es->start = orig_es.start;
+ es->len = orig_es.len;
+ goto out;
+ }
+ } else {
+ es->start = end + 1;
+ es->len = len2;
+ }
+ goto out;
+ }
+
+ if (len1 > 0) {
+ node = rb_next(&es->rb_node);
+ if (node)
+ es = rb_entry(node, struct extent_status, rb_node);
+ else
+ es = NULL;
+ }
+
+ while (es && extent_status_end(es) <= end) {
+ node = rb_next(&es->rb_node);
+ rb_erase(&es->rb_node, &tree->root);
+ ext4_es_free_extent(es);
+ if (!node) {
+ es = NULL;
+ break;
+ }
+ 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;
+ }
+
+out:
+ write_unlock(&EXT4_I(inode)->i_es_lock);
+ ext4_es_print_tree(inode);
+ return err;
+}