1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Copyright (C) 2016 Oracle. All Rights Reserved.
4 * Author: Darrick J. Wong <darrick.wong@oracle.com>
5 */
6 #include "xfs.h"
7 #include "xfs_fs.h"
8 #include "xfs_shared.h"
9 #include "xfs_format.h"
10 #include "xfs_log_format.h"
11 #include "xfs_trans_resv.h"
12 #include "xfs_mount.h"
13 #include "xfs_alloc.h"
14 #include "xfs_errortag.h"
15 #include "xfs_error.h"
16 #include "xfs_trace.h"
17 #include "xfs_trans.h"
18 #include "xfs_rmap_btree.h"
19 #include "xfs_btree.h"
20 #include "xfs_refcount_btree.h"
21 #include "xfs_ialloc_btree.h"
22 #include "xfs_ag.h"
23 #include "xfs_ag_resv.h"
24
25 /*
26 * Per-AG Block Reservations
27 *
28 * For some kinds of allocation group metadata structures, it is advantageous
29 * to reserve a small number of blocks in each AG so that future expansions of
30 * that data structure do not encounter ENOSPC because errors during a btree
31 * split cause the filesystem to go offline.
32 *
33 * Prior to the introduction of reflink, this wasn't an issue because the free
34 * space btrees maintain a reserve of space (the AGFL) to handle any expansion
35 * that may be necessary; and allocations of other metadata (inodes, BMBT,
36 * dir/attr) aren't restricted to a single AG. However, with reflink it is
37 * possible to allocate all the space in an AG, have subsequent reflink/CoW
38 * activity expand the refcount btree, and discover that there's no space left
39 * to handle that expansion. Since we can calculate the maximum size of the
40 * refcount btree, we can reserve space for it and avoid ENOSPC.
41 *
42 * Handling per-AG reservations consists of three changes to the allocator's
43 * behavior: First, because these reservations are always needed, we decrease
44 * the ag_max_usable counter to reflect the size of the AG after the reserved
45 * blocks are taken. Second, the reservations must be reflected in the
46 * fdblocks count to maintain proper accounting. Third, each AG must maintain
47 * its own reserved block counter so that we can calculate the amount of space
48 * that must remain free to maintain the reservations. Fourth, the "remaining
49 * reserved blocks" count must be used when calculating the length of the
50 * longest free extent in an AG and to clamp maxlen in the per-AG allocation
51 * functions. In other words, we maintain a virtual allocation via in-core
52 * accounting tricks so that we don't have to clean up after a crash. :)
53 *
54 * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
55 * values via struct xfs_alloc_arg or directly to the xfs_free_extent
56 * function. It might seem a little funny to maintain a reservoir of blocks
57 * to feed another reservoir, but the AGFL only holds enough blocks to get
58 * through the next transaction. The per-AG reservation is to ensure (we
59 * hope) that each AG never runs out of blocks. Each data structure wanting
60 * to use the reservation system should update ask/used in xfs_ag_resv_init.
61 */
62
63 /*
64 * Are we critically low on blocks? For now we'll define that as the number
65 * of blocks we can get our hands on being less than 10% of what we reserved
66 * or less than some arbitrary number (maximum btree height).
67 */
68 bool
69 xfs_ag_resv_critical(
70 struct xfs_perag *pag,
71 enum xfs_ag_resv_type type)
72 {
73 xfs_extlen_t avail;
74 xfs_extlen_t orig;
75
76 switch (type) {
77 case XFS_AG_RESV_METADATA:
78 avail = pag->pagf_freeblks - pag->pag_rmapbt_resv.ar_reserved;
79 orig = pag->pag_meta_resv.ar_asked;
80 break;
81 case XFS_AG_RESV_RMAPBT:
82 avail = pag->pagf_freeblks + pag->pagf_flcount -
83 pag->pag_meta_resv.ar_reserved;
84 orig = pag->pag_rmapbt_resv.ar_asked;
85 break;
86 default:
87 ASSERT(0);
88 return false;
89 }
90
91 trace_xfs_ag_resv_critical(pag, type, avail);
92
93 /* Critically low if less than 10% or max btree height remains. */
94 return XFS_TEST_ERROR(avail < orig / 10 ||
95 avail < pag->pag_mount->m_agbtree_maxlevels,
96 pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL);
97 }
98
99 /*
100 * How many blocks are reserved but not used, and therefore must not be
101 * allocated away?
102 */
103 xfs_extlen_t
104 xfs_ag_resv_needed(
105 struct xfs_perag *pag,
106 enum xfs_ag_resv_type type)
107 {
108 xfs_extlen_t len;
109
110 len = pag->pag_meta_resv.ar_reserved + pag->pag_rmapbt_resv.ar_reserved;
111 switch (type) {
112 case XFS_AG_RESV_METADATA:
113 case XFS_AG_RESV_RMAPBT:
114 len -= xfs_perag_resv(pag, type)->ar_reserved;
115 break;
116 case XFS_AG_RESV_NONE:
117 /* empty */
118 break;
119 default:
120 ASSERT(0);
121 }
122
123 trace_xfs_ag_resv_needed(pag, type, len);
124
125 return len;
126 }
127
128 /* Clean out a reservation */
129 static void
130 __xfs_ag_resv_free(
131 struct xfs_perag *pag,
132 enum xfs_ag_resv_type type)
133 {
134 struct xfs_ag_resv *resv;
135 xfs_extlen_t oldresv;
136
137 trace_xfs_ag_resv_free(pag, type, 0);
138
139 resv = xfs_perag_resv(pag, type);
140 if (pag->pag_agno == 0)
141 pag->pag_mount->m_ag_max_usable += resv->ar_asked;
142 /*
143 * RMAPBT blocks come from the AGFL and AGFL blocks are always
144 * considered "free", so whatever was reserved at mount time must be
145 * given back at umount.
146 */
147 if (type == XFS_AG_RESV_RMAPBT)
148 oldresv = resv->ar_orig_reserved;
149 else
150 oldresv = resv->ar_reserved;
151 xfs_add_fdblocks(pag->pag_mount, oldresv);
152 resv->ar_reserved = 0;
153 resv->ar_asked = 0;
154 resv->ar_orig_reserved = 0;
155 }
156
157 /* Free a per-AG reservation. */
158 void
159 xfs_ag_resv_free(
160 struct xfs_perag *pag)
161 {
162 __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
163 __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
164 }
165
166 static int
167 __xfs_ag_resv_init(
168 struct xfs_perag *pag,
169 enum xfs_ag_resv_type type,
170 xfs_extlen_t ask,
171 xfs_extlen_t used)
172 {
173 struct xfs_mount *mp = pag->pag_mount;
174 struct xfs_ag_resv *resv;
175 int error;
176 xfs_extlen_t hidden_space;
177
178 if (used > ask)
179 ask = used;
180
181 switch (type) {
182 case XFS_AG_RESV_RMAPBT:
183 /*
184 * Space taken by the rmapbt is not subtracted from fdblocks
185 * because the rmapbt lives in the free space. Here we must
186 * subtract the entire reservation from fdblocks so that we
187 * always have blocks available for rmapbt expansion.
188 */
189 hidden_space = ask;
190 break;
191 case XFS_AG_RESV_METADATA:
192 /*
193 * Space taken by all other metadata btrees are accounted
194 * on-disk as used space. We therefore only hide the space
195 * that is reserved but not used by the trees.
196 */
197 hidden_space = ask - used;
198 break;
199 default:
200 ASSERT(0);
201 return -EINVAL;
202 }
203
204 if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
205 error = -ENOSPC;
206 else
207 error = xfs_dec_fdblocks(mp, hidden_space, true);
208 if (error) {
209 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
210 error, _RET_IP_);
211 xfs_warn(mp,
212 "Per-AG reservation for AG %u failed. Filesystem may run out of space.",
213 pag->pag_agno);
214 return error;
215 }
216
217 /*
218 * Reduce the maximum per-AG allocation length by however much we're
219 * trying to reserve for an AG. Since this is a filesystem-wide
220 * counter, we only make the adjustment for AG 0. This assumes that
221 * there aren't any AGs hungrier for per-AG reservation than AG 0.
222 */
223 if (pag->pag_agno == 0)
224 mp->m_ag_max_usable -= ask;
225
226 resv = xfs_perag_resv(pag, type);
227 resv->ar_asked = ask;
228 resv->ar_orig_reserved = hidden_space;
229 resv->ar_reserved = ask - used;
230
231 trace_xfs_ag_resv_init(pag, type, ask);
232 return 0;
233 }
234
235 /* Create a per-AG block reservation. */
236 int
237 xfs_ag_resv_init(
238 struct xfs_perag *pag,
239 struct xfs_trans *tp)
240 {
241 struct xfs_mount *mp = pag->pag_mount;
242 xfs_extlen_t ask;
243 xfs_extlen_t used;
244 int error = 0, error2;
245 bool has_resv = false;
246
247 /* Create the metadata reservation. */
248 if (pag->pag_meta_resv.ar_asked == 0) {
249 ask = used = 0;
250
251 error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask, &used);
252 if (error)
253 goto out;
254
255 error = xfs_finobt_calc_reserves(pag, tp, &ask, &used);
256 if (error)
257 goto out;
258
259 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
260 ask, used);
261 if (error) {
262 /*
263 * Because we didn't have per-AG reservations when the
264 * finobt feature was added we might not be able to
265 * reserve all needed blocks. Warn and fall back to the
266 * old and potentially buggy code in that case, but
267 * ensure we do have the reservation for the refcountbt.
268 */
269 ask = used = 0;
270
271 mp->m_finobt_nores = true;
272
273 error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask,
274 &used);
275 if (error)
276 goto out;
277
278 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
279 ask, used);
280 if (error)
281 goto out;
282 }
283 if (ask)
284 has_resv = true;
285 }
286
287 /* Create the RMAPBT metadata reservation */
288 if (pag->pag_rmapbt_resv.ar_asked == 0) {
289 ask = used = 0;
290
291 error = xfs_rmapbt_calc_reserves(mp, tp, pag, &ask, &used);
292 if (error)
293 goto out;
294
295 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
296 if (error)
297 goto out;
298 if (ask)
299 has_resv = true;
300 }
301
302 out:
303 /*
304 * Initialize the pagf if we have at least one active reservation on the
305 * AG. This may have occurred already via reservation calculation, but
306 * fall back to an explicit init to ensure the in-core allocbt usage
307 * counters are initialized as soon as possible. This is important
308 * because filesystems with large perag reservations are susceptible to
309 * free space reservation problems that the allocbt counter is used to
310 * address.
311 */
312 if (has_resv) {
313 error2 = xfs_alloc_read_agf(pag, tp, 0, NULL);
314 if (error2)
315 return error2;
316
317 /*
318 * If there isn't enough space in the AG to satisfy the
319 * reservation, let the caller know that there wasn't enough
320 * space. Callers are responsible for deciding what to do
321 * next, since (in theory) we can stumble along with
322 * insufficient reservation if data blocks are being freed to
323 * replenish the AG's free space.
324 */
325 if (!error &&
326 xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
327 xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved >
328 pag->pagf_freeblks + pag->pagf_flcount)
329 error = -ENOSPC;
330 }
331
332 return error;
333 }
334
335 /* Allocate a block from the reservation. */
336 void
337 xfs_ag_resv_alloc_extent(
338 struct xfs_perag *pag,
339 enum xfs_ag_resv_type type,
340 struct xfs_alloc_arg *args)
341 {
342 struct xfs_ag_resv *resv;
343 xfs_extlen_t len;
344 uint field;
345
346 trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
347
348 switch (type) {
349 case XFS_AG_RESV_AGFL:
350 return;
351 case XFS_AG_RESV_METADATA:
352 case XFS_AG_RESV_RMAPBT:
353 resv = xfs_perag_resv(pag, type);
354 break;
355 default:
356 ASSERT(0);
357 fallthrough;
358 case XFS_AG_RESV_NONE:
359 field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
360 XFS_TRANS_SB_FDBLOCKS;
361 xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
362 return;
363 }
364
365 len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
366 resv->ar_reserved -= len;
367 if (type == XFS_AG_RESV_RMAPBT)
368 return;
369 /* Allocations of reserved blocks only need on-disk sb updates... */
370 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
371 /* ...but non-reserved blocks need in-core and on-disk updates. */
372 if (args->len > len)
373 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
374 -((int64_t)args->len - len));
375 }
376
377 /* Free a block to the reservation. */
378 void
379 xfs_ag_resv_free_extent(
380 struct xfs_perag *pag,
381 enum xfs_ag_resv_type type,
382 struct xfs_trans *tp,
383 xfs_extlen_t len)
384 {
385 xfs_extlen_t leftover;
386 struct xfs_ag_resv *resv;
387
388 trace_xfs_ag_resv_free_extent(pag, type, len);
389
390 switch (type) {
391 case XFS_AG_RESV_AGFL:
392 return;
393 case XFS_AG_RESV_METADATA:
394 case XFS_AG_RESV_RMAPBT:
395 resv = xfs_perag_resv(pag, type);
396 break;
397 default:
398 ASSERT(0);
399 fallthrough;
400 case XFS_AG_RESV_NONE:
401 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
402 fallthrough;
403 case XFS_AG_RESV_IGNORE:
404 return;
405 }
406
407 leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
408 resv->ar_reserved += leftover;
409 if (type == XFS_AG_RESV_RMAPBT)
410 return;
411 /* Freeing into the reserved pool only requires on-disk update... */
412 xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
413 /* ...but freeing beyond that requires in-core and on-disk update. */
414 if (len > leftover)
415 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
416 }
417
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