From: Zheng Liu Subject: [PATCH 2/8 v3] ext4: add operations on extent status tree Date: Fri, 26 Oct 2012 21:23:39 +0800 Message-ID: <1351257825-3701-3-git-send-email-wenqing.lz@taobao.com> References: <1351257825-3701-1-git-send-email-wenqing.lz@taobao.com> Cc: tytso@mit.edu, hughd@google.com, xiaoqiangnk@gmail.com, achender@linux.vnet.ibm.com, lczerner@redhat.com, Zheng Liu To: linux-ext4@vger.kernel.org, jeff.liu@oracle.com Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:42938 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755066Ab2JZNMv (ORCPT ); Fri, 26 Oct 2012 09:12:51 -0400 Received: by mail-pb0-f46.google.com with SMTP id rr4so2768601pbb.19 for ; Fri, 26 Oct 2012 06:12:50 -0700 (PDT) In-Reply-To: <1351257825-3701-1-git-send-email-wenqing.lz@taobao.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Zheng Liu This patch adds operations on a extent status tree. CC: "Theodore Ts'o" CC: Lukas Czerner Signed-off-by: Yongqiang Yang Signed-off-by: Allison Henderson Signed-off-by: Hugh Dickins Signed-off-by: Zheng Liu --- v3 <- v2: - improve try_to_merge_left/right() functions (Hugh, Thank you) - fix some bugs on inserting/removing an extent - use i_es_lock to protect extent status tree - add some comments to describe the extent status tree and future works in step2 fs/ext4/Makefile | 2 +- fs/ext4/extents_status.c | 491 +++++++++++++++++++++++++++++++++++++++++++++++ fs/ext4/extents_status.h | 20 ++ 3 files changed, 512 insertions(+), 1 deletion(-) 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..048ae8c --- /dev/null +++ b/fs/ext4/extents_status.c @@ -0,0 +1,491 @@ +/* + * fs/ext4/extents_status.c + * + * Written by Yongqiang Yang + * Modified by + * Allison Henderson + * Hugh Dickins + * Zheng Liu + * + * Ext4 extents status tree core functions. + */ +#include +#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. 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. + * + * + * ========================================================================== + * 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; +} 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 */ -- 1.7.12.rc2.18.g61b472e