[RFC][PATCH 02/10 v1][RESEND] ext4: add operations on extent status tree

Zheng Liu
2012-07-22T07:51:21Z

This patch adds operations on a extent status tree.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: Allison Henderson <achender@linux.vnet.ibm.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
---
fs/ext4/Makefile | 2 +-
fs/ext4/extents_status.c | 418 ++++++++++++++++++++++++++++++++++++++++++++++
fs/ext4/extents_status.h | 17 ++
3 files changed, 436 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..bd4e589
--- /dev/null
+++ b/fs/ext4/extents_status.c
@@ -0,0 +1,418 @@
+/*
+ * fs/ext4/extents_status.c
+ *
+ * Written by Yongqiang Yang <xiaoqiangnk@gmail.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 SE_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)
+{
+ if (es->start + es->len < es->start)
+ return (ext4_lblk_t)-1;
+ return es->start + es->len;
+}
+
+/*
+ * 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 next block beyond the found extent.
+ * 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;
+ struct extent_status *es1;
+ struct rb_node *node;
+ ext4_lblk_t ret = EXT_MAX_BLOCKS;
+
+ es->len = 0;
+ tree = &EXT4_I(inode)->i_es_tree;
+ es1 = __es_tree_search(&tree->root, es->start);
+ 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 (extent_status_end(es1) == es->start) {
+ 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)) {
+ 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_add_space: adds a space to a delayed extent tree.
+ * Caller holds inode->i_data_sem.
+ *
+ * ext4_es_add_space is callyed by ext4_dealyed_write_begin and
+ * ext4_es_remove_space.
+ *
+ * Return 0 on success, error code on failure.
+ */
+int ext4_es_add_space(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;
+
+ 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 && extent_status_end(es) == offset) {
+ 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) {
+ 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 && es->start <= offset &&
+ extent_status_end(es) >= end) {
+ 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 (end == es->start) {
+ es->len += len;
+ es->start = offset;
+ goto out;
+ }
+ p = &(*p)->rb_left;
+ } else if (offset >= extent_status_end(es)) {
+ if (extent_status_end(es) == offset) {
+ 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_space() 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_space(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;
+ 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_add_space(inode, end, len2);
+ if (err) {
+ es->start = orig_es.start;
+ es->len = orig_es.len;
+ return err;
+ }
+ } else {
+ es->start = end;
+ 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) {
+ len1 = extent_status_end(es) - end;
+ es->start = end;
+ 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 d87fd71..8fe8084 100644
--- a/fs/ext4/extents_status.h
+++ b/fs/ext4/extents_status.h
@@ -8,6 +8,12 @@
#ifndef _EXT4_EXTENTS_STATUS_H
#define _EXT4_EXTENTS_STATUS_H

+#ifdef ES_DEBUG
+#define es_debug(a...) printk(a)
+#else
+#define es_debug(a...)
+#endif
+
struct extent_status {
struct rb_node rb_node;
ext4_lblk_t start; /* first block extent covers */
@@ -19,4 +25,15 @@ 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_add_space(struct inode *inode, ext4_lblk_t start,
+ ext4_lblk_t len);
+extern int ext4_es_remove_space(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