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654598be ZL |
1 | /* |
2 | * fs/ext4/extents_status.c | |
3 | * | |
4 | * Written by Yongqiang Yang <xiaoqiangnk@gmail.com> | |
5 | * Modified by | |
6 | * Allison Henderson <achender@linux.vnet.ibm.com> | |
7 | * Hugh Dickins <hughd@google.com> | |
8 | * Zheng Liu <wenqing.lz@taobao.com> | |
9 | * | |
10 | * Ext4 extents status tree core functions. | |
11 | */ | |
12 | #include <linux/rbtree.h> | |
13 | #include "ext4.h" | |
14 | #include "extents_status.h" | |
15 | #include "ext4_extents.h" | |
16 | ||
17 | /* | |
18 | * According to previous discussion in Ext4 Developer Workshop, we | |
19 | * will introduce a new structure called io tree to track all extent | |
20 | * status in order to solve some problems that we have met | |
21 | * (e.g. Reservation space warning), and provide extent-level locking. | |
22 | * Delay extent tree is the first step to achieve this goal. It is | |
23 | * original built by Yongqiang Yang. At that time it is called delay | |
24 | * extent tree, whose goal is only track delay extent in memory to | |
25 | * simplify the implementation of fiemap and bigalloc, and introduce | |
26 | * lseek SEEK_DATA/SEEK_HOLE support. That is why it is still called | |
27 | * delay extent tree at the following comment. But for better | |
28 | * understand what it does, it has been rename to extent status tree. | |
29 | * | |
30 | * Currently the first step has been done. All delay extents are | |
31 | * tracked in the tree. It maintains the delay extent when a delay | |
32 | * allocation is issued, and the delay extent is written out or | |
33 | * invalidated. Therefore the implementation of fiemap and bigalloc | |
34 | * are simplified, and SEEK_DATA/SEEK_HOLE are introduced. | |
35 | * | |
36 | * The following comment describes the implemenmtation of extent | |
37 | * status tree and future works. | |
38 | */ | |
39 | ||
40 | /* | |
41 | * extents status tree implementation for ext4. | |
42 | * | |
43 | * | |
44 | * ========================================================================== | |
45 | * Extents status encompass delayed extents and extent locks | |
46 | * | |
47 | * 1. Why delayed extent implementation ? | |
48 | * | |
49 | * Without delayed extent, ext4 identifies a delayed extent by looking | |
50 | * up page cache, this has several deficiencies - complicated, buggy, | |
51 | * and inefficient code. | |
52 | * | |
53 | * FIEMAP, SEEK_HOLE/DATA, bigalloc, punch hole and writeout all need | |
54 | * to know if a block or a range of blocks are belonged to a delayed | |
55 | * extent. | |
56 | * | |
57 | * Let us have a look at how they do without delayed extents implementation. | |
58 | * -- FIEMAP | |
59 | * FIEMAP looks up page cache to identify delayed allocations from holes. | |
60 | * | |
61 | * -- SEEK_HOLE/DATA | |
62 | * SEEK_HOLE/DATA has the same problem as FIEMAP. | |
63 | * | |
64 | * -- bigalloc | |
65 | * bigalloc looks up page cache to figure out if a block is | |
66 | * already under delayed allocation or not to determine whether | |
67 | * quota reserving is needed for the cluster. | |
68 | * | |
69 | * -- punch hole | |
70 | * punch hole looks up page cache to identify a delayed extent. | |
71 | * | |
72 | * -- writeout | |
73 | * Writeout looks up whole page cache to see if a buffer is | |
74 | * mapped, If there are not very many delayed buffers, then it is | |
75 | * time comsuming. | |
76 | * | |
77 | * With delayed extents implementation, FIEMAP, SEEK_HOLE/DATA, | |
78 | * bigalloc and writeout can figure out if a block or a range of | |
79 | * blocks is under delayed allocation(belonged to a delayed extent) or | |
80 | * not by searching the delayed extent tree. | |
81 | * | |
82 | * | |
83 | * ========================================================================== | |
84 | * 2. ext4 delayed extents impelmentation | |
85 | * | |
86 | * -- delayed extent | |
87 | * A delayed extent is a range of blocks which are contiguous | |
88 | * logically and under delayed allocation. Unlike extent in | |
89 | * ext4, delayed extent in ext4 is a in-memory struct, there is | |
90 | * no corresponding on-disk data. There is no limit on length of | |
91 | * delayed extent, so a delayed extent can contain as many blocks | |
92 | * as they are contiguous logically. | |
93 | * | |
94 | * -- delayed extent tree | |
95 | * Every inode has a delayed extent tree and all under delayed | |
96 | * allocation blocks are added to the tree as delayed extents. | |
97 | * Delayed extents in the tree are ordered by logical block no. | |
98 | * | |
99 | * -- operations on a delayed extent tree | |
100 | * There are three operations on a delayed extent tree: find next | |
101 | * delayed extent, adding a space(a range of blocks) and removing | |
102 | * a space. | |
103 | * | |
104 | * -- race on a delayed extent tree | |
105 | * Delayed extent tree is protected inode->i_es_lock. | |
106 | * | |
107 | * | |
108 | * ========================================================================== | |
109 | * 3. performance analysis | |
110 | * -- overhead | |
111 | * 1. There is a cache extent for write access, so if writes are | |
112 | * not very random, adding space operaions are in O(1) time. | |
113 | * | |
114 | * -- gain | |
115 | * 2. Code is much simpler, more readable, more maintainable and | |
116 | * more efficient. | |
117 | * | |
118 | * | |
119 | * ========================================================================== | |
120 | * 4. TODO list | |
121 | * -- Track all extent status | |
122 | * | |
123 | * -- Improve get block process | |
124 | * | |
125 | * -- Extent-level locking | |
126 | */ | |
127 | ||
128 | static struct kmem_cache *ext4_es_cachep; | |
129 | ||
130 | int __init ext4_init_es(void) | |
131 | { | |
132 | ext4_es_cachep = KMEM_CACHE(extent_status, SLAB_RECLAIM_ACCOUNT); | |
133 | if (ext4_es_cachep == NULL) | |
134 | return -ENOMEM; | |
135 | return 0; | |
136 | } | |
137 | ||
138 | void ext4_exit_es(void) | |
139 | { | |
140 | if (ext4_es_cachep) | |
141 | kmem_cache_destroy(ext4_es_cachep); | |
142 | } | |
143 | ||
144 | void ext4_es_init_tree(struct ext4_es_tree *tree) | |
145 | { | |
146 | tree->root = RB_ROOT; | |
147 | tree->cache_es = NULL; | |
148 | } | |
149 | ||
150 | #ifdef ES_DEBUG__ | |
151 | static void ext4_es_print_tree(struct inode *inode) | |
152 | { | |
153 | struct ext4_es_tree *tree; | |
154 | struct rb_node *node; | |
155 | ||
156 | printk(KERN_DEBUG "status extents for inode %lu:", inode->i_ino); | |
157 | tree = &EXT4_I(inode)->i_es_tree; | |
158 | node = rb_first(&tree->root); | |
159 | while (node) { | |
160 | struct extent_status *es; | |
161 | es = rb_entry(node, struct extent_status, rb_node); | |
162 | printk(KERN_DEBUG " [%u/%u)", es->start, es->len); | |
163 | node = rb_next(node); | |
164 | } | |
165 | printk(KERN_DEBUG "\n"); | |
166 | } | |
167 | #else | |
168 | #define ext4_es_print_tree(inode) | |
169 | #endif | |
170 | ||
171 | static inline ext4_lblk_t extent_status_end(struct extent_status *es) | |
172 | { | |
173 | BUG_ON(es->start + es->len < es->start); | |
174 | return es->start + es->len - 1; | |
175 | } | |
176 | ||
177 | /* | |
178 | * search through the tree for an delayed extent with a given offset. If | |
179 | * it can't be found, try to find next extent. | |
180 | */ | |
181 | static struct extent_status *__es_tree_search(struct rb_root *root, | |
182 | ext4_lblk_t offset) | |
183 | { | |
184 | struct rb_node *node = root->rb_node; | |
185 | struct extent_status *es = NULL; | |
186 | ||
187 | while (node) { | |
188 | es = rb_entry(node, struct extent_status, rb_node); | |
189 | if (offset < es->start) | |
190 | node = node->rb_left; | |
191 | else if (offset > extent_status_end(es)) | |
192 | node = node->rb_right; | |
193 | else | |
194 | return es; | |
195 | } | |
196 | ||
197 | if (es && offset < es->start) | |
198 | return es; | |
199 | ||
200 | if (es && offset > extent_status_end(es)) { | |
201 | node = rb_next(&es->rb_node); | |
202 | return node ? rb_entry(node, struct extent_status, rb_node) : | |
203 | NULL; | |
204 | } | |
205 | ||
206 | return NULL; | |
207 | } | |
208 | ||
209 | /* | |
210 | * ext4_es_find_extent: find the 1st delayed extent covering @es->start | |
211 | * if it exists, otherwise, the next extent after @es->start. | |
212 | * | |
213 | * @inode: the inode which owns delayed extents | |
214 | * @es: delayed extent that we found | |
215 | * | |
216 | * Returns the first block of the next extent after es, otherwise | |
217 | * EXT_MAX_BLOCKS if no delay extent is found. | |
218 | * Delayed extent is returned via @es. | |
219 | */ | |
220 | ext4_lblk_t ext4_es_find_extent(struct inode *inode, struct extent_status *es) | |
221 | { | |
222 | struct ext4_es_tree *tree = NULL; | |
223 | struct extent_status *es1 = NULL; | |
224 | struct rb_node *node; | |
225 | ext4_lblk_t ret = EXT_MAX_BLOCKS; | |
226 | ||
227 | read_lock(&EXT4_I(inode)->i_es_lock); | |
228 | tree = &EXT4_I(inode)->i_es_tree; | |
229 | ||
230 | /* find delay extent in cache firstly */ | |
231 | if (tree->cache_es) { | |
232 | es1 = tree->cache_es; | |
233 | if (in_range(es->start, es1->start, es1->len)) { | |
234 | es_debug("%u cached by [%u/%u)\n", | |
235 | es->start, es1->start, es1->len); | |
236 | goto out; | |
237 | } | |
238 | } | |
239 | ||
240 | es->len = 0; | |
241 | es1 = __es_tree_search(&tree->root, es->start); | |
242 | ||
243 | out: | |
244 | if (es1) { | |
245 | tree->cache_es = es1; | |
246 | es->start = es1->start; | |
247 | es->len = es1->len; | |
248 | node = rb_next(&es1->rb_node); | |
249 | if (node) { | |
250 | es1 = rb_entry(node, struct extent_status, rb_node); | |
251 | ret = es1->start; | |
252 | } | |
253 | } | |
254 | ||
255 | read_unlock(&EXT4_I(inode)->i_es_lock); | |
256 | return ret; | |
257 | } | |
258 | ||
259 | static struct extent_status * | |
260 | ext4_es_alloc_extent(ext4_lblk_t start, ext4_lblk_t len) | |
261 | { | |
262 | struct extent_status *es; | |
263 | es = kmem_cache_alloc(ext4_es_cachep, GFP_ATOMIC); | |
264 | if (es == NULL) | |
265 | return NULL; | |
266 | es->start = start; | |
267 | es->len = len; | |
268 | return es; | |
269 | } | |
270 | ||
271 | static void ext4_es_free_extent(struct extent_status *es) | |
272 | { | |
273 | kmem_cache_free(ext4_es_cachep, es); | |
274 | } | |
275 | ||
276 | static struct extent_status * | |
277 | ext4_es_try_to_merge_left(struct ext4_es_tree *tree, struct extent_status *es) | |
278 | { | |
279 | struct extent_status *es1; | |
280 | struct rb_node *node; | |
281 | ||
282 | node = rb_prev(&es->rb_node); | |
283 | if (!node) | |
284 | return es; | |
285 | ||
286 | es1 = rb_entry(node, struct extent_status, rb_node); | |
287 | if (es->start == extent_status_end(es1) + 1) { | |
288 | es1->len += es->len; | |
289 | rb_erase(&es->rb_node, &tree->root); | |
290 | ext4_es_free_extent(es); | |
291 | es = es1; | |
292 | } | |
293 | ||
294 | return es; | |
295 | } | |
296 | ||
297 | static struct extent_status * | |
298 | ext4_es_try_to_merge_right(struct ext4_es_tree *tree, struct extent_status *es) | |
299 | { | |
300 | struct extent_status *es1; | |
301 | struct rb_node *node; | |
302 | ||
303 | node = rb_next(&es->rb_node); | |
304 | if (!node) | |
305 | return es; | |
306 | ||
307 | es1 = rb_entry(node, struct extent_status, rb_node); | |
308 | if (es1->start == extent_status_end(es) + 1) { | |
309 | es->len += es1->len; | |
310 | rb_erase(node, &tree->root); | |
311 | ext4_es_free_extent(es1); | |
312 | } | |
313 | ||
314 | return es; | |
315 | } | |
316 | ||
317 | static int __es_insert_extent(struct ext4_es_tree *tree, ext4_lblk_t offset, | |
318 | ext4_lblk_t len) | |
319 | { | |
320 | struct rb_node **p = &tree->root.rb_node; | |
321 | struct rb_node *parent = NULL; | |
322 | struct extent_status *es; | |
323 | ext4_lblk_t end = offset + len - 1; | |
324 | ||
325 | BUG_ON(end < offset); | |
326 | es = tree->cache_es; | |
327 | if (es && offset == (extent_status_end(es) + 1)) { | |
328 | es_debug("cached by [%u/%u)\n", es->start, es->len); | |
329 | es->len += len; | |
330 | es = ext4_es_try_to_merge_right(tree, es); | |
331 | goto out; | |
332 | } else if (es && es->start == end + 1) { | |
333 | es_debug("cached by [%u/%u)\n", es->start, es->len); | |
334 | es->start = offset; | |
335 | es->len += len; | |
336 | es = ext4_es_try_to_merge_left(tree, es); | |
337 | goto out; | |
338 | } else if (es && es->start <= offset && | |
339 | end <= extent_status_end(es)) { | |
340 | es_debug("cached by [%u/%u)\n", es->start, es->len); | |
341 | goto out; | |
342 | } | |
343 | ||
344 | while (*p) { | |
345 | parent = *p; | |
346 | es = rb_entry(parent, struct extent_status, rb_node); | |
347 | ||
348 | if (offset < es->start) { | |
349 | if (es->start == end + 1) { | |
350 | es->start = offset; | |
351 | es->len += len; | |
352 | es = ext4_es_try_to_merge_left(tree, es); | |
353 | goto out; | |
354 | } | |
355 | p = &(*p)->rb_left; | |
356 | } else if (offset > extent_status_end(es)) { | |
357 | if (offset == extent_status_end(es) + 1) { | |
358 | es->len += len; | |
359 | es = ext4_es_try_to_merge_right(tree, es); | |
360 | goto out; | |
361 | } | |
362 | p = &(*p)->rb_right; | |
363 | } else { | |
364 | if (extent_status_end(es) <= end) | |
365 | es->len = offset - es->start + len; | |
366 | goto out; | |
367 | } | |
368 | } | |
369 | ||
370 | es = ext4_es_alloc_extent(offset, len); | |
371 | if (!es) | |
372 | return -ENOMEM; | |
373 | rb_link_node(&es->rb_node, parent, p); | |
374 | rb_insert_color(&es->rb_node, &tree->root); | |
375 | ||
376 | out: | |
377 | tree->cache_es = es; | |
378 | return 0; | |
379 | } | |
380 | ||
381 | /* | |
382 | * ext4_es_insert_extent() adds a space to a delayed extent tree. | |
383 | * Caller holds inode->i_es_lock. | |
384 | * | |
385 | * ext4_es_insert_extent is called by ext4_da_write_begin and | |
386 | * ext4_es_remove_extent. | |
387 | * | |
388 | * Return 0 on success, error code on failure. | |
389 | */ | |
390 | int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t offset, | |
391 | ext4_lblk_t len) | |
392 | { | |
393 | struct ext4_es_tree *tree; | |
394 | int err = 0; | |
395 | ||
396 | es_debug("add [%u/%u) to extent status tree of inode %lu\n", | |
397 | offset, len, inode->i_ino); | |
398 | ||
399 | write_lock(&EXT4_I(inode)->i_es_lock); | |
400 | tree = &EXT4_I(inode)->i_es_tree; | |
401 | err = __es_insert_extent(tree, offset, len); | |
402 | write_unlock(&EXT4_I(inode)->i_es_lock); | |
403 | ||
404 | ext4_es_print_tree(inode); | |
405 | ||
406 | return err; | |
407 | } | |
408 | ||
409 | /* | |
410 | * ext4_es_remove_extent() removes a space from a delayed extent tree. | |
411 | * Caller holds inode->i_es_lock. | |
412 | * | |
413 | * Return 0 on success, error code on failure. | |
414 | */ | |
415 | int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t offset, | |
416 | ext4_lblk_t len) | |
417 | { | |
418 | struct rb_node *node; | |
419 | struct ext4_es_tree *tree; | |
420 | struct extent_status *es; | |
421 | struct extent_status orig_es; | |
422 | ext4_lblk_t len1, len2, end; | |
423 | int err = 0; | |
424 | ||
425 | es_debug("remove [%u/%u) from extent status tree of inode %lu\n", | |
426 | offset, len, inode->i_ino); | |
427 | ||
428 | end = offset + len - 1; | |
429 | BUG_ON(end < offset); | |
430 | write_lock(&EXT4_I(inode)->i_es_lock); | |
431 | tree = &EXT4_I(inode)->i_es_tree; | |
432 | es = __es_tree_search(&tree->root, offset); | |
433 | if (!es) | |
434 | goto out; | |
435 | if (es->start > end) | |
436 | goto out; | |
437 | ||
438 | /* Simply invalidate cache_es. */ | |
439 | tree->cache_es = NULL; | |
440 | ||
441 | orig_es.start = es->start; | |
442 | orig_es.len = es->len; | |
443 | len1 = offset > es->start ? offset - es->start : 0; | |
444 | len2 = extent_status_end(es) > end ? | |
445 | extent_status_end(es) - end : 0; | |
446 | if (len1 > 0) | |
447 | es->len = len1; | |
448 | if (len2 > 0) { | |
449 | if (len1 > 0) { | |
450 | err = __es_insert_extent(tree, end + 1, len2); | |
451 | if (err) { | |
452 | es->start = orig_es.start; | |
453 | es->len = orig_es.len; | |
454 | goto out; | |
455 | } | |
456 | } else { | |
457 | es->start = end + 1; | |
458 | es->len = len2; | |
459 | } | |
460 | goto out; | |
461 | } | |
462 | ||
463 | if (len1 > 0) { | |
464 | node = rb_next(&es->rb_node); | |
465 | if (node) | |
466 | es = rb_entry(node, struct extent_status, rb_node); | |
467 | else | |
468 | es = NULL; | |
469 | } | |
470 | ||
471 | while (es && extent_status_end(es) <= end) { | |
472 | node = rb_next(&es->rb_node); | |
473 | rb_erase(&es->rb_node, &tree->root); | |
474 | ext4_es_free_extent(es); | |
475 | if (!node) { | |
476 | es = NULL; | |
477 | break; | |
478 | } | |
479 | es = rb_entry(node, struct extent_status, rb_node); | |
480 | } | |
481 | ||
482 | if (es && es->start < end + 1) { | |
483 | len1 = extent_status_end(es) - end; | |
484 | es->start = end + 1; | |
485 | es->len = len1; | |
486 | } | |
487 | ||
488 | out: | |
489 | write_unlock(&EXT4_I(inode)->i_es_lock); | |
490 | ext4_es_print_tree(inode); | |
491 | return err; | |
492 | } |