2 * fs/ext4/extents_status.c
4 * Written by Yongqiang Yang <xiaoqiangnk@gmail.com>
6 * Allison Henderson <achender@linux.vnet.ibm.com>
7 * Hugh Dickins <hughd@google.com>
8 * Zheng Liu <wenqing.lz@taobao.com>
10 * Ext4 extents status tree core functions.
12 #include <linux/rbtree.h>
14 #include "extents_status.h"
15 #include "ext4_extents.h"
17 #include <trace/events/ext4.h>
20 * According to previous discussion in Ext4 Developer Workshop, we
21 * will introduce a new structure called io tree to track all extent
22 * status in order to solve some problems that we have met
23 * (e.g. Reservation space warning), and provide extent-level locking.
24 * Delay extent tree is the first step to achieve this goal. It is
25 * original built by Yongqiang Yang. At that time it is called delay
26 * extent tree, whose goal is only track delayed extents in memory to
27 * simplify the implementation of fiemap and bigalloc, and introduce
28 * lseek SEEK_DATA/SEEK_HOLE support. That is why it is still called
29 * delay extent tree at the first commit. But for better understand
30 * what it does, it has been rename to extent status tree.
33 * Currently the first step has been done. All delayed extents are
34 * tracked in the tree. It maintains the delayed extent when a delayed
35 * allocation is issued, and the delayed extent is written out or
36 * invalidated. Therefore the implementation of fiemap and bigalloc
37 * are simplified, and SEEK_DATA/SEEK_HOLE are introduced.
39 * The following comment describes the implemenmtation of extent
40 * status tree and future works.
43 * In this step all extent status are tracked by extent status tree.
44 * Thus, we can first try to lookup a block mapping in this tree before
45 * finding it in extent tree. Hence, single extent cache can be removed
46 * because extent status tree can do a better job. Extents in status
47 * tree are loaded on-demand. Therefore, the extent status tree may not
48 * contain all of the extents in a file. Meanwhile we define a shrinker
49 * to reclaim memory from extent status tree because fragmented extent
50 * tree will make status tree cost too much memory. written/unwritten/-
51 * hole extents in the tree will be reclaimed by this shrinker when we
52 * are under high memory pressure. Delayed extents will not be
53 * reclimed because fiemap, bigalloc, and seek_data/hole need it.
57 * Extent status tree implementation for ext4.
60 * ==========================================================================
61 * Extent status tree tracks all extent status.
63 * 1. Why we need to implement extent status tree?
65 * Without extent status tree, ext4 identifies a delayed extent by looking
66 * up page cache, this has several deficiencies - complicated, buggy,
67 * and inefficient code.
69 * FIEMAP, SEEK_HOLE/DATA, bigalloc, and writeout all need to know if a
70 * block or a range of blocks are belonged to a delayed extent.
72 * Let us have a look at how they do without extent status tree.
74 * FIEMAP looks up page cache to identify delayed allocations from holes.
77 * SEEK_HOLE/DATA has the same problem as FIEMAP.
80 * bigalloc looks up page cache to figure out if a block is
81 * already under delayed allocation or not to determine whether
82 * quota reserving is needed for the cluster.
85 * Writeout looks up whole page cache to see if a buffer is
86 * mapped, If there are not very many delayed buffers, then it is
89 * With extent status tree implementation, FIEMAP, SEEK_HOLE/DATA,
90 * bigalloc and writeout can figure out if a block or a range of
91 * blocks is under delayed allocation(belonged to a delayed extent) or
92 * not by searching the extent tree.
95 * ==========================================================================
96 * 2. Ext4 extent status tree impelmentation
99 * A extent is a range of blocks which are contiguous logically and
100 * physically. Unlike extent in extent tree, this extent in ext4 is
101 * a in-memory struct, there is no corresponding on-disk data. There
102 * is no limit on length of extent, so an extent can contain as many
103 * blocks as they are contiguous logically and physically.
105 * -- extent status tree
106 * Every inode has an extent status tree and all allocation blocks
107 * are added to the tree with different status. The extent in the
108 * tree are ordered by logical block no.
110 * -- operations on a extent status tree
111 * There are three important operations on a delayed extent tree: find
112 * next extent, adding a extent(a range of blocks) and removing a extent.
114 * -- race on a extent status tree
115 * Extent status tree is protected by inode->i_es_lock.
117 * -- memory consumption
118 * Fragmented extent tree will make extent status tree cost too much
119 * memory. Hence, we will reclaim written/unwritten/hole extents from
120 * the tree under a heavy memory pressure.
123 * ==========================================================================
124 * 3. Performance analysis
127 * 1. There is a cache extent for write access, so if writes are
128 * not very random, adding space operaions are in O(1) time.
131 * 2. Code is much simpler, more readable, more maintainable and
135 * ==========================================================================
138 * -- Refactor delayed space reservation
140 * -- Extent-level locking
143 static struct kmem_cache *ext4_es_cachep;
145 static int __es_insert_extent(struct ext4_es_tree *tree,
146 struct extent_status *newes);
147 static int __es_remove_extent(struct ext4_es_tree *tree, ext4_lblk_t lblk,
150 int __init ext4_init_es(void)
152 ext4_es_cachep = KMEM_CACHE(extent_status, SLAB_RECLAIM_ACCOUNT);
153 if (ext4_es_cachep == NULL)
158 void ext4_exit_es(void)
161 kmem_cache_destroy(ext4_es_cachep);
164 void ext4_es_init_tree(struct ext4_es_tree *tree)
166 tree->root = RB_ROOT;
167 tree->cache_es = NULL;
171 static void ext4_es_print_tree(struct inode *inode)
173 struct ext4_es_tree *tree;
174 struct rb_node *node;
176 printk(KERN_DEBUG "status extents for inode %lu:", inode->i_ino);
177 tree = &EXT4_I(inode)->i_es_tree;
178 node = rb_first(&tree->root);
180 struct extent_status *es;
181 es = rb_entry(node, struct extent_status, rb_node);
182 printk(KERN_DEBUG " [%u/%u)", es->es_lblk, es->es_len);
183 node = rb_next(node);
185 printk(KERN_DEBUG "\n");
188 #define ext4_es_print_tree(inode)
191 static inline ext4_lblk_t ext4_es_end(struct extent_status *es)
193 BUG_ON(es->es_lblk + es->es_len < es->es_lblk);
194 return es->es_lblk + es->es_len - 1;
198 * search through the tree for an delayed extent with a given offset. If
199 * it can't be found, try to find next extent.
201 static struct extent_status *__es_tree_search(struct rb_root *root,
204 struct rb_node *node = root->rb_node;
205 struct extent_status *es = NULL;
208 es = rb_entry(node, struct extent_status, rb_node);
209 if (lblk < es->es_lblk)
210 node = node->rb_left;
211 else if (lblk > ext4_es_end(es))
212 node = node->rb_right;
217 if (es && lblk < es->es_lblk)
220 if (es && lblk > ext4_es_end(es)) {
221 node = rb_next(&es->rb_node);
222 return node ? rb_entry(node, struct extent_status, rb_node) :
230 * ext4_es_find_extent: find the 1st delayed extent covering @es->lblk
231 * if it exists, otherwise, the next extent after @es->lblk.
233 * @inode: the inode which owns delayed extents
234 * @es: delayed extent that we found
236 * Returns the first block of the next extent after es, otherwise
237 * EXT_MAX_BLOCKS if no delay extent is found.
238 * Delayed extent is returned via @es.
240 ext4_lblk_t ext4_es_find_extent(struct inode *inode, struct extent_status *es)
242 struct ext4_es_tree *tree = NULL;
243 struct extent_status *es1 = NULL;
244 struct rb_node *node;
245 ext4_lblk_t ret = EXT_MAX_BLOCKS;
247 trace_ext4_es_find_extent_enter(inode, es->es_lblk);
249 read_lock(&EXT4_I(inode)->i_es_lock);
250 tree = &EXT4_I(inode)->i_es_tree;
252 /* find delay extent in cache firstly */
253 if (tree->cache_es) {
254 es1 = tree->cache_es;
255 if (in_range(es->es_lblk, es1->es_lblk, es1->es_len)) {
256 es_debug("%u cached by [%u/%u)\n",
257 es->es_lblk, es1->es_lblk, es1->es_len);
263 es1 = __es_tree_search(&tree->root, es->es_lblk);
267 tree->cache_es = es1;
268 es->es_lblk = es1->es_lblk;
269 es->es_len = es1->es_len;
270 node = rb_next(&es1->rb_node);
272 es1 = rb_entry(node, struct extent_status, rb_node);
277 read_unlock(&EXT4_I(inode)->i_es_lock);
279 trace_ext4_es_find_extent_exit(inode, es, ret);
283 static struct extent_status *
284 ext4_es_alloc_extent(ext4_lblk_t lblk, ext4_lblk_t len)
286 struct extent_status *es;
287 es = kmem_cache_alloc(ext4_es_cachep, GFP_ATOMIC);
295 static void ext4_es_free_extent(struct extent_status *es)
297 kmem_cache_free(ext4_es_cachep, es);
301 * Check whether or not two extents can be merged
303 * - logical block number is contiguous
305 static int ext4_es_can_be_merged(struct extent_status *es1,
306 struct extent_status *es2)
308 if (es1->es_lblk + es1->es_len != es2->es_lblk)
314 static struct extent_status *
315 ext4_es_try_to_merge_left(struct ext4_es_tree *tree, struct extent_status *es)
317 struct extent_status *es1;
318 struct rb_node *node;
320 node = rb_prev(&es->rb_node);
324 es1 = rb_entry(node, struct extent_status, rb_node);
325 if (ext4_es_can_be_merged(es1, es)) {
326 es1->es_len += es->es_len;
327 rb_erase(&es->rb_node, &tree->root);
328 ext4_es_free_extent(es);
335 static struct extent_status *
336 ext4_es_try_to_merge_right(struct ext4_es_tree *tree, struct extent_status *es)
338 struct extent_status *es1;
339 struct rb_node *node;
341 node = rb_next(&es->rb_node);
345 es1 = rb_entry(node, struct extent_status, rb_node);
346 if (ext4_es_can_be_merged(es, es1)) {
347 es->es_len += es1->es_len;
348 rb_erase(node, &tree->root);
349 ext4_es_free_extent(es1);
355 static int __es_insert_extent(struct ext4_es_tree *tree,
356 struct extent_status *newes)
358 struct rb_node **p = &tree->root.rb_node;
359 struct rb_node *parent = NULL;
360 struct extent_status *es;
364 es = rb_entry(parent, struct extent_status, rb_node);
366 if (newes->es_lblk < es->es_lblk) {
367 if (ext4_es_can_be_merged(newes, es)) {
369 * Here we can modify es_lblk directly
370 * because it isn't overlapped.
372 es->es_lblk = newes->es_lblk;
373 es->es_len += newes->es_len;
374 es = ext4_es_try_to_merge_left(tree, es);
378 } else if (newes->es_lblk > ext4_es_end(es)) {
379 if (ext4_es_can_be_merged(es, newes)) {
380 es->es_len += newes->es_len;
381 es = ext4_es_try_to_merge_right(tree, es);
391 es = ext4_es_alloc_extent(newes->es_lblk, newes->es_len);
394 rb_link_node(&es->rb_node, parent, p);
395 rb_insert_color(&es->rb_node, &tree->root);
403 * ext4_es_insert_extent() adds a space to a extent status tree.
405 * ext4_es_insert_extent is called by ext4_da_write_begin and
406 * ext4_es_remove_extent.
408 * Return 0 on success, error code on failure.
410 int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
413 struct ext4_es_tree *tree;
414 struct extent_status newes;
415 ext4_lblk_t end = lblk + len - 1;
418 trace_ext4_es_insert_extent(inode, lblk, len);
419 es_debug("add [%u/%u) to extent status tree of inode %lu\n",
420 lblk, len, inode->i_ino);
424 newes.es_lblk = lblk;
427 write_lock(&EXT4_I(inode)->i_es_lock);
428 tree = &EXT4_I(inode)->i_es_tree;
429 err = __es_remove_extent(tree, lblk, end);
432 err = __es_insert_extent(tree, &newes);
435 write_unlock(&EXT4_I(inode)->i_es_lock);
437 ext4_es_print_tree(inode);
442 static int __es_remove_extent(struct ext4_es_tree *tree, ext4_lblk_t lblk,
445 struct rb_node *node;
446 struct extent_status *es;
447 struct extent_status orig_es;
448 ext4_lblk_t len1, len2;
451 es = __es_tree_search(&tree->root, lblk);
454 if (es->es_lblk > end)
457 /* Simply invalidate cache_es. */
458 tree->cache_es = NULL;
460 orig_es.es_lblk = es->es_lblk;
461 orig_es.es_len = es->es_len;
462 len1 = lblk > es->es_lblk ? lblk - es->es_lblk : 0;
463 len2 = ext4_es_end(es) > end ? ext4_es_end(es) - end : 0;
468 struct extent_status newes;
470 newes.es_lblk = end + 1;
472 err = __es_insert_extent(tree, &newes);
474 es->es_lblk = orig_es.es_lblk;
475 es->es_len = orig_es.es_len;
479 es->es_lblk = end + 1;
486 node = rb_next(&es->rb_node);
488 es = rb_entry(node, struct extent_status, rb_node);
493 while (es && ext4_es_end(es) <= end) {
494 node = rb_next(&es->rb_node);
495 rb_erase(&es->rb_node, &tree->root);
496 ext4_es_free_extent(es);
501 es = rb_entry(node, struct extent_status, rb_node);
504 if (es && es->es_lblk < end + 1) {
505 len1 = ext4_es_end(es) - end;
506 es->es_lblk = end + 1;
515 * ext4_es_remove_extent() removes a space from a extent status tree.
517 * Return 0 on success, error code on failure.
519 int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
522 struct ext4_es_tree *tree;
526 trace_ext4_es_remove_extent(inode, lblk, len);
527 es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
528 lblk, len, inode->i_ino);
530 end = lblk + len - 1;
533 tree = &EXT4_I(inode)->i_es_tree;
535 write_lock(&EXT4_I(inode)->i_es_lock);
536 err = __es_remove_extent(tree, lblk, end);
537 write_unlock(&EXT4_I(inode)->i_es_lock);
538 ext4_es_print_tree(inode);