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) %llu %llx",
183 es
->es_lblk
, es
->es_len
,
184 ext4_es_pblock(es
), ext4_es_status(es
));
185 node
= rb_next(node
);
187 printk(KERN_DEBUG
"\n");
190 #define ext4_es_print_tree(inode)
193 static inline ext4_lblk_t
ext4_es_end(struct extent_status
*es
)
195 BUG_ON(es
->es_lblk
+ es
->es_len
< es
->es_lblk
);
196 return es
->es_lblk
+ es
->es_len
- 1;
200 * search through the tree for an delayed extent with a given offset. If
201 * it can't be found, try to find next extent.
203 static struct extent_status
*__es_tree_search(struct rb_root
*root
,
206 struct rb_node
*node
= root
->rb_node
;
207 struct extent_status
*es
= NULL
;
210 es
= rb_entry(node
, struct extent_status
, rb_node
);
211 if (lblk
< es
->es_lblk
)
212 node
= node
->rb_left
;
213 else if (lblk
> ext4_es_end(es
))
214 node
= node
->rb_right
;
219 if (es
&& lblk
< es
->es_lblk
)
222 if (es
&& lblk
> ext4_es_end(es
)) {
223 node
= rb_next(&es
->rb_node
);
224 return node
? rb_entry(node
, struct extent_status
, rb_node
) :
232 * ext4_es_find_extent: find the 1st delayed extent covering @es->lblk
233 * if it exists, otherwise, the next extent after @es->lblk.
235 * @inode: the inode which owns delayed extents
236 * @es: delayed extent that we found
238 * Returns the first block of the next extent after es, otherwise
239 * EXT_MAX_BLOCKS if no extent is found.
240 * Delayed extent is returned via @es.
242 ext4_lblk_t
ext4_es_find_extent(struct inode
*inode
, struct extent_status
*es
)
244 struct ext4_es_tree
*tree
= NULL
;
245 struct extent_status
*es1
= NULL
;
246 struct rb_node
*node
;
247 ext4_lblk_t ret
= EXT_MAX_BLOCKS
;
249 trace_ext4_es_find_extent_enter(inode
, es
->es_lblk
);
251 read_lock(&EXT4_I(inode
)->i_es_lock
);
252 tree
= &EXT4_I(inode
)->i_es_tree
;
254 /* find extent in cache firstly */
255 es
->es_len
= es
->es_pblk
= 0;
256 if (tree
->cache_es
) {
257 es1
= tree
->cache_es
;
258 if (in_range(es
->es_lblk
, es1
->es_lblk
, es1
->es_len
)) {
259 es_debug("%u cached by [%u/%u) %llu %llx\n",
260 es
->es_lblk
, es1
->es_lblk
, es1
->es_len
,
261 ext4_es_pblock(es1
), ext4_es_status(es1
));
266 es1
= __es_tree_search(&tree
->root
, es
->es_lblk
);
270 tree
->cache_es
= es1
;
271 es
->es_lblk
= es1
->es_lblk
;
272 es
->es_len
= es1
->es_len
;
273 es
->es_pblk
= es1
->es_pblk
;
274 node
= rb_next(&es1
->rb_node
);
276 es1
= rb_entry(node
, struct extent_status
, rb_node
);
281 read_unlock(&EXT4_I(inode
)->i_es_lock
);
283 trace_ext4_es_find_extent_exit(inode
, es
, ret
);
287 static struct extent_status
*
288 ext4_es_alloc_extent(ext4_lblk_t lblk
, ext4_lblk_t len
, ext4_fsblk_t pblk
)
290 struct extent_status
*es
;
291 es
= kmem_cache_alloc(ext4_es_cachep
, GFP_ATOMIC
);
300 static void ext4_es_free_extent(struct extent_status
*es
)
302 kmem_cache_free(ext4_es_cachep
, es
);
306 * Check whether or not two extents can be merged
308 * - logical block number is contiguous
309 * - physical block number is contiguous
312 static int ext4_es_can_be_merged(struct extent_status
*es1
,
313 struct extent_status
*es2
)
315 if (es1
->es_lblk
+ es1
->es_len
!= es2
->es_lblk
)
318 if (ext4_es_status(es1
) != ext4_es_status(es2
))
321 if ((ext4_es_is_written(es1
) || ext4_es_is_unwritten(es1
)) &&
322 (ext4_es_pblock(es1
) + es1
->es_len
!= ext4_es_pblock(es2
)))
328 static struct extent_status
*
329 ext4_es_try_to_merge_left(struct ext4_es_tree
*tree
, struct extent_status
*es
)
331 struct extent_status
*es1
;
332 struct rb_node
*node
;
334 node
= rb_prev(&es
->rb_node
);
338 es1
= rb_entry(node
, struct extent_status
, rb_node
);
339 if (ext4_es_can_be_merged(es1
, es
)) {
340 es1
->es_len
+= es
->es_len
;
341 rb_erase(&es
->rb_node
, &tree
->root
);
342 ext4_es_free_extent(es
);
349 static struct extent_status
*
350 ext4_es_try_to_merge_right(struct ext4_es_tree
*tree
, struct extent_status
*es
)
352 struct extent_status
*es1
;
353 struct rb_node
*node
;
355 node
= rb_next(&es
->rb_node
);
359 es1
= rb_entry(node
, struct extent_status
, rb_node
);
360 if (ext4_es_can_be_merged(es
, es1
)) {
361 es
->es_len
+= es1
->es_len
;
362 rb_erase(node
, &tree
->root
);
363 ext4_es_free_extent(es1
);
369 static int __es_insert_extent(struct ext4_es_tree
*tree
,
370 struct extent_status
*newes
)
372 struct rb_node
**p
= &tree
->root
.rb_node
;
373 struct rb_node
*parent
= NULL
;
374 struct extent_status
*es
;
378 es
= rb_entry(parent
, struct extent_status
, rb_node
);
380 if (newes
->es_lblk
< es
->es_lblk
) {
381 if (ext4_es_can_be_merged(newes
, es
)) {
383 * Here we can modify es_lblk directly
384 * because it isn't overlapped.
386 es
->es_lblk
= newes
->es_lblk
;
387 es
->es_len
+= newes
->es_len
;
388 if (ext4_es_is_written(es
) ||
389 ext4_es_is_unwritten(es
))
390 ext4_es_store_pblock(es
,
392 es
= ext4_es_try_to_merge_left(tree
, es
);
396 } else if (newes
->es_lblk
> ext4_es_end(es
)) {
397 if (ext4_es_can_be_merged(es
, newes
)) {
398 es
->es_len
+= newes
->es_len
;
399 es
= ext4_es_try_to_merge_right(tree
, es
);
409 es
= ext4_es_alloc_extent(newes
->es_lblk
, newes
->es_len
,
413 rb_link_node(&es
->rb_node
, parent
, p
);
414 rb_insert_color(&es
->rb_node
, &tree
->root
);
422 * ext4_es_insert_extent() adds a space to a extent status tree.
424 * ext4_es_insert_extent is called by ext4_da_write_begin and
425 * ext4_es_remove_extent.
427 * Return 0 on success, error code on failure.
429 int ext4_es_insert_extent(struct inode
*inode
, ext4_lblk_t lblk
,
430 ext4_lblk_t len
, ext4_fsblk_t pblk
,
431 unsigned long long status
)
433 struct ext4_es_tree
*tree
;
434 struct extent_status newes
;
435 ext4_lblk_t end
= lblk
+ len
- 1;
438 es_debug("add [%u/%u) %llu %llx to extent status tree of inode %lu\n",
439 lblk
, len
, pblk
, status
, inode
->i_ino
);
443 newes
.es_lblk
= lblk
;
445 ext4_es_store_pblock(&newes
, pblk
);
446 ext4_es_store_status(&newes
, status
);
447 trace_ext4_es_insert_extent(inode
, &newes
);
449 write_lock(&EXT4_I(inode
)->i_es_lock
);
450 tree
= &EXT4_I(inode
)->i_es_tree
;
451 err
= __es_remove_extent(tree
, lblk
, end
);
454 err
= __es_insert_extent(tree
, &newes
);
457 write_unlock(&EXT4_I(inode
)->i_es_lock
);
459 ext4_es_print_tree(inode
);
464 static int __es_remove_extent(struct ext4_es_tree
*tree
, ext4_lblk_t lblk
,
467 struct rb_node
*node
;
468 struct extent_status
*es
;
469 struct extent_status orig_es
;
470 ext4_lblk_t len1
, len2
;
474 es
= __es_tree_search(&tree
->root
, lblk
);
477 if (es
->es_lblk
> end
)
480 /* Simply invalidate cache_es. */
481 tree
->cache_es
= NULL
;
483 orig_es
.es_lblk
= es
->es_lblk
;
484 orig_es
.es_len
= es
->es_len
;
485 orig_es
.es_pblk
= es
->es_pblk
;
487 len1
= lblk
> es
->es_lblk
? lblk
- es
->es_lblk
: 0;
488 len2
= ext4_es_end(es
) > end
? ext4_es_end(es
) - end
: 0;
493 struct extent_status newes
;
495 newes
.es_lblk
= end
+ 1;
497 if (ext4_es_is_written(&orig_es
) ||
498 ext4_es_is_unwritten(&orig_es
)) {
499 block
= ext4_es_pblock(&orig_es
) +
500 orig_es
.es_len
- len2
;
501 ext4_es_store_pblock(&newes
, block
);
503 ext4_es_store_status(&newes
, ext4_es_status(&orig_es
));
504 err
= __es_insert_extent(tree
, &newes
);
506 es
->es_lblk
= orig_es
.es_lblk
;
507 es
->es_len
= orig_es
.es_len
;
511 es
->es_lblk
= end
+ 1;
513 if (ext4_es_is_written(es
) ||
514 ext4_es_is_unwritten(es
)) {
515 block
= orig_es
.es_pblk
+ orig_es
.es_len
- len2
;
516 ext4_es_store_pblock(es
, block
);
523 node
= rb_next(&es
->rb_node
);
525 es
= rb_entry(node
, struct extent_status
, rb_node
);
530 while (es
&& ext4_es_end(es
) <= end
) {
531 node
= rb_next(&es
->rb_node
);
532 rb_erase(&es
->rb_node
, &tree
->root
);
533 ext4_es_free_extent(es
);
538 es
= rb_entry(node
, struct extent_status
, rb_node
);
541 if (es
&& es
->es_lblk
< end
+ 1) {
542 ext4_lblk_t orig_len
= es
->es_len
;
544 len1
= ext4_es_end(es
) - end
;
545 es
->es_lblk
= end
+ 1;
547 if (ext4_es_is_written(es
) || ext4_es_is_unwritten(es
)) {
548 block
= es
->es_pblk
+ orig_len
- len1
;
549 ext4_es_store_pblock(es
, block
);
558 * ext4_es_remove_extent() removes a space from a extent status tree.
560 * Return 0 on success, error code on failure.
562 int ext4_es_remove_extent(struct inode
*inode
, ext4_lblk_t lblk
,
565 struct ext4_es_tree
*tree
;
569 trace_ext4_es_remove_extent(inode
, lblk
, len
);
570 es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
571 lblk
, len
, inode
->i_ino
);
573 end
= lblk
+ len
- 1;
576 tree
= &EXT4_I(inode
)->i_es_tree
;
578 write_lock(&EXT4_I(inode
)->i_es_lock
);
579 err
= __es_remove_extent(tree
, lblk
, end
);
580 write_unlock(&EXT4_I(inode
)->i_es_lock
);
581 ext4_es_print_tree(inode
);
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