Message-Id: <1345615545-26133-3-git-send-email-wenqing.lz@taobao.com>
Date:	Wed, 22 Aug 2012 14:05:39 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:	Lukas Czerner <lczerner@...hat.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Allison Henderson <achender@...ux.vnet.ibm.com>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: [RFC][PATCH 2/8 v2] ext4: add operations on extent status tree

From: Zheng Liu <wenqing.lz@...bao.com>

This patch adds operations on a extent status tree.

CC: Lukas Czerner <lczerner@...hat.com>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
Signed-off-by: Allison Henderson <achender@...ux.vnet.ibm.com>
Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
---
v2 <- v1:
 - add a BUG_ON to do a sanity check in extent_status_end()
 - fix off-by-one problem in extent_status_end() according to Lukas's comment
 - add more detailed comments in ext4_es_find_extent()
 - try to lookup in extent tree cache firstly in ext4_es_find_extent()
 - rename ext4_es_add_space to ext4_es_insert_extent
 - rename ext4_es_remove_space to ext4_es_remove_extent

Hi Lukas,

I have fix some problems according to your advices, but there still has a little
comments that haven't be applied.  I introduce my point of view in here.  I
don't change es_debug functions because I see that ext_debug() is defined in
ext4_extents.h.  So I think that maybe we should keep es_debug(), and it is
consistent with extent tree.  Meanwhile I don't remove es_debug() in
ext4_es_remove_extent, although later we will add a tracepoint in this function
because IMO they ared used by different purposes.  One is used for debugging,
and another is used for observing the status of filesystem.  What do you think?

Regards,
Zheng

 fs/ext4/Makefile         |    2 +-
 fs/ext4/extents_status.c |  434 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/ext4/extents_status.h |   20 ++
 3 files changed, 455 insertions(+), 1 deletions(-)
 create mode 100644 fs/ext4/extents_status.c

diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 56fd8f86..41f22be 100644
--- a/fs/ext4/Makefile
+++ b/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
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
new file mode 100644
index 0000000..ccb7e2b
--- /dev/null
+++ b/fs/ext4/extents_status.c
@@ -0,0 +1,434 @@
+/*
+ *  fs/ext4/extents_status.c
+ *
+ * Written by Yongqiang Yang <xiaoqiangnk@...il.com>
+ * Modified by
+ *	Allison Henderson <achender@...ux.vnet.ibm.com>
+ *	Zheng Liu <wenqing.lz@...bao.com>
+ *
+ * Ext4 extents status tree core functions.
+ */
+#include <linux/rbtree.h>
+#include "ext4.h"
+#include "extents_status.h"
+#include "ext4_extents.h"
+
+/*
+ * 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 dealyed 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_data_sem like extent tree.
+ *
+ *
+ * ==========================================================================
+ * 3. performance analysis
+ *   --	overhead
+ *	1. Apart from operations on a delayed extent tree, we need to
+ *	down_write(inode->i_data_sem) in delayed write path to maintain delayed
+ *	extent tree, this can have impact on parallel read-write and write-write
+ *
+ *	2. There is a cache extent for write access, so if writes are not very
+ *	random, adding space operaions are in O(1) time.
+ *
+ *   --	gain
+ *	3. Code is much simpler, more readable, more maintainable and
+ *      more efficient.
+ */
+
+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;
+
+	tree = &EXT4_I(inode)->i_es_tree;
+
+	/* find delay extent in cache */
+	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;
+		}
+	}
+
+	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_NOFS);
+	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 void 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;
+
+	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);
+		if (es == tree->cache_es)
+			tree->cache_es = es1;
+		ext4_es_free_extent(es);
+	}
+}
+
+static void 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;
+
+	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);
+		if (es1 == tree->cache_es)
+			tree->cache_es = es;
+		ext4_es_free_extent(es1);
+	}
+}
+
+/*
+ * ext4_es_insert_extent: adds a space to a delayed extent tree.
+ * Caller holds inode->i_data_sem.
+ *
+ * ext4_es_insert_extent is callyed by ext4_dealyed_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 = &EXT4_I(inode)->i_es_tree;
+	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;
+	es_debug("add [%u/%u) to extent status tree of inode %lu\n",
+		 offset, len, inode->i_ino);
+
+	if (es && offset == (extent_status_end(es) + 1)) {
+		es_debug("cached by [%u/%u)\n", es->start, es->len);
+		es->len += len;
+		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;
+		ext4_es_try_to_merge_left(tree, es);
+		goto out;
+	} else if (es && in_range(offset, es->start, es->len)) {
+		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->len += len;
+				es->start = offset;
+				goto out;
+			}
+			p = &(*p)->rb_left;
+		} else if (offset > extent_status_end(es)) {
+			if (offset == extent_status_end(es) + 1) {
+				es->len += len;
+				goto out;
+			}
+			p = &(*p)->rb_right;
+		} else
+			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;
+	ext4_es_print_tree(inode);
+
+	return 0;
+}
+
+/*
+ * ext4_es_remove_extent() removes a space from a delayed extent tree.
+ * Caller holds inode->i_data_sem.
+ *
+ * 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;
+
+	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);
+	tree = &EXT4_I(inode)->i_es_tree;
+	es = __es_tree_search(&tree->root, offset);
+	if (!es)
+		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) {
+			int err;
+			err = ext4_es_insert_extent(inode, end + 1, len2);
+			if (err) {
+				es->start = orig_es.start;
+				es->len = orig_es.len;
+				return err;
+			}
+		} 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:
+	ext4_es_print_tree(inode);
+	return 0;
+}
diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
index 8be2ab9..077f82d 100644
--- a/fs/ext4/extents_status.h
+++ b/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 */
-- 
1.7.4.1

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