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>

fs/ext4/Makefile

@@ -7,7 +7,7 @@ obj-$(CONFIG_EXT4_FS) += ext4.o
 ext4-y	:= balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
 		ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \
 		ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o \
-		mmp.o indirect.o
+		mmp.o indirect.o extents_status.o
 
 ext4-$(CONFIG_EXT4_FS_XATTR)		+= xattr.o xattr_user.o xattr_trusted.o
 ext4-$(CONFIG_EXT4_FS_POSIX_ACL)	+= acl.o

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;
+}

fs/ext4/extents_status.h

@@ -11,6 +11,15 @@
 #ifndef _EXT4_EXTENTS_STATUS_H
 #define _EXT4_EXTENTS_STATUS_H
 
+/*
+ * Turn on ES_DEBUG__ to get lots of info about extent status operations.
+ */
+#ifdef ES_DEBUG__
+#define es_debug(fmt, ...)	printk(fmt, ##__VA_ARGS__)
+#else
+#define es_debug(fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
+#endif
+
 struct extent_status {
 	struct rb_node rb_node;
 	ext4_lblk_t start;	/* first block extent covers */
@@ -22,4 +31,15 @@ struct ext4_es_tree {
 	struct extent_status *cache_es;	/* recently accessed extent */
 };
 
+extern int __init ext4_init_es(void);
+extern void ext4_exit_es(void);
+extern void ext4_es_init_tree(struct ext4_es_tree *tree);
+
+extern int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t start,
+				 ext4_lblk_t len);
+extern int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t start,
+				 ext4_lblk_t len);
+extern ext4_lblk_t ext4_es_find_extent(struct inode *inode,
+				struct extent_status *es);
+
 #endif /* _EXT4_EXTENTS_STATUS_H */