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 */
68bool
69xfs_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 */
103xfs_extlen_t
104xfs_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 */
129static int
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 int error;
137
138 trace_xfs_ag_resv_free(pag, type, 0);
139
140 resv = xfs_perag_resv(pag, type: type);
141 if (pag->pag_agno == 0)
142 pag->pag_mount->m_ag_max_usable += resv->ar_asked;
143 /*
144 * RMAPBT blocks come from the AGFL and AGFL blocks are always
145 * considered "free", so whatever was reserved at mount time must be
146 * given back at umount.
147 */
148 if (type == XFS_AG_RESV_RMAPBT)
149 oldresv = resv->ar_orig_reserved;
150 else
151 oldresv = resv->ar_reserved;
152 error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
153 resv->ar_reserved = 0;
154 resv->ar_asked = 0;
155 resv->ar_orig_reserved = 0;
156
157 if (error)
158 trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
159 error, _RET_IP_);
160 return error;
161}
162
163/* Free a per-AG reservation. */
164int
165xfs_ag_resv_free(
166 struct xfs_perag *pag)
167{
168 int error;
169 int err2;
170
171 error = __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
172 err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
173 if (err2 && !error)
174 error = err2;
175 return error;
176}
177
178static int
179__xfs_ag_resv_init(
180 struct xfs_perag *pag,
181 enum xfs_ag_resv_type type,
182 xfs_extlen_t ask,
183 xfs_extlen_t used)
184{
185 struct xfs_mount *mp = pag->pag_mount;
186 struct xfs_ag_resv *resv;
187 int error;
188 xfs_extlen_t hidden_space;
189
190 if (used > ask)
191 ask = used;
192
193 switch (type) {
194 case XFS_AG_RESV_RMAPBT:
195 /*
196 * Space taken by the rmapbt is not subtracted from fdblocks
197 * because the rmapbt lives in the free space. Here we must
198 * subtract the entire reservation from fdblocks so that we
199 * always have blocks available for rmapbt expansion.
200 */
201 hidden_space = ask;
202 break;
203 case XFS_AG_RESV_METADATA:
204 /*
205 * Space taken by all other metadata btrees are accounted
206 * on-disk as used space. We therefore only hide the space
207 * that is reserved but not used by the trees.
208 */
209 hidden_space = ask - used;
210 break;
211 default:
212 ASSERT(0);
213 return -EINVAL;
214 }
215
216 if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
217 error = -ENOSPC;
218 else
219 error = xfs_mod_fdblocks(mp, -(int64_t)hidden_space, true);
220 if (error) {
221 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
222 error, _RET_IP_);
223 xfs_warn(mp,
224"Per-AG reservation for AG %u failed. Filesystem may run out of space.",
225 pag->pag_agno);
226 return error;
227 }
228
229 /*
230 * Reduce the maximum per-AG allocation length by however much we're
231 * trying to reserve for an AG. Since this is a filesystem-wide
232 * counter, we only make the adjustment for AG 0. This assumes that
233 * there aren't any AGs hungrier for per-AG reservation than AG 0.
234 */
235 if (pag->pag_agno == 0)
236 mp->m_ag_max_usable -= ask;
237
238 resv = xfs_perag_resv(pag, type: type);
239 resv->ar_asked = ask;
240 resv->ar_orig_reserved = hidden_space;
241 resv->ar_reserved = ask - used;
242
243 trace_xfs_ag_resv_init(pag, type, ask);
244 return 0;
245}
246
247/* Create a per-AG block reservation. */
248int
249xfs_ag_resv_init(
250 struct xfs_perag *pag,
251 struct xfs_trans *tp)
252{
253 struct xfs_mount *mp = pag->pag_mount;
254 xfs_extlen_t ask;
255 xfs_extlen_t used;
256 int error = 0, error2;
257 bool has_resv = false;
258
259 /* Create the metadata reservation. */
260 if (pag->pag_meta_resv.ar_asked == 0) {
261 ask = used = 0;
262
263 error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask, &used);
264 if (error)
265 goto out;
266
267 error = xfs_finobt_calc_reserves(pag, tp, &ask, &used);
268 if (error)
269 goto out;
270
271 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
272 ask, used);
273 if (error) {
274 /*
275 * Because we didn't have per-AG reservations when the
276 * finobt feature was added we might not be able to
277 * reserve all needed blocks. Warn and fall back to the
278 * old and potentially buggy code in that case, but
279 * ensure we do have the reservation for the refcountbt.
280 */
281 ask = used = 0;
282
283 mp->m_finobt_nores = true;
284
285 error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask,
286 &used);
287 if (error)
288 goto out;
289
290 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
291 ask, used);
292 if (error)
293 goto out;
294 }
295 if (ask)
296 has_resv = true;
297 }
298
299 /* Create the RMAPBT metadata reservation */
300 if (pag->pag_rmapbt_resv.ar_asked == 0) {
301 ask = used = 0;
302
303 error = xfs_rmapbt_calc_reserves(mp, tp, pag, &ask, &used);
304 if (error)
305 goto out;
306
307 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
308 if (error)
309 goto out;
310 if (ask)
311 has_resv = true;
312 }
313
314out:
315 /*
316 * Initialize the pagf if we have at least one active reservation on the
317 * AG. This may have occurred already via reservation calculation, but
318 * fall back to an explicit init to ensure the in-core allocbt usage
319 * counters are initialized as soon as possible. This is important
320 * because filesystems with large perag reservations are susceptible to
321 * free space reservation problems that the allocbt counter is used to
322 * address.
323 */
324 if (has_resv) {
325 error2 = xfs_alloc_read_agf(pag, tp, 0, NULL);
326 if (error2)
327 return error2;
328
329 /*
330 * If there isn't enough space in the AG to satisfy the
331 * reservation, let the caller know that there wasn't enough
332 * space. Callers are responsible for deciding what to do
333 * next, since (in theory) we can stumble along with
334 * insufficient reservation if data blocks are being freed to
335 * replenish the AG's free space.
336 */
337 if (!error &&
338 xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
339 xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved >
340 pag->pagf_freeblks + pag->pagf_flcount)
341 error = -ENOSPC;
342 }
343
344 return error;
345}
346
347/* Allocate a block from the reservation. */
348void
349xfs_ag_resv_alloc_extent(
350 struct xfs_perag *pag,
351 enum xfs_ag_resv_type type,
352 struct xfs_alloc_arg *args)
353{
354 struct xfs_ag_resv *resv;
355 xfs_extlen_t len;
356 uint field;
357
358 trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
359
360 switch (type) {
361 case XFS_AG_RESV_AGFL:
362 return;
363 case XFS_AG_RESV_METADATA:
364 case XFS_AG_RESV_RMAPBT:
365 resv = xfs_perag_resv(pag, type: type);
366 break;
367 default:
368 ASSERT(0);
369 fallthrough;
370 case XFS_AG_RESV_NONE:
371 field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
372 XFS_TRANS_SB_FDBLOCKS;
373 xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
374 return;
375 }
376
377 len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
378 resv->ar_reserved -= len;
379 if (type == XFS_AG_RESV_RMAPBT)
380 return;
381 /* Allocations of reserved blocks only need on-disk sb updates... */
382 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
383 /* ...but non-reserved blocks need in-core and on-disk updates. */
384 if (args->len > len)
385 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
386 -((int64_t)args->len - len));
387}
388
389/* Free a block to the reservation. */
390void
391xfs_ag_resv_free_extent(
392 struct xfs_perag *pag,
393 enum xfs_ag_resv_type type,
394 struct xfs_trans *tp,
395 xfs_extlen_t len)
396{
397 xfs_extlen_t leftover;
398 struct xfs_ag_resv *resv;
399
400 trace_xfs_ag_resv_free_extent(pag, type, len);
401
402 switch (type) {
403 case XFS_AG_RESV_AGFL:
404 return;
405 case XFS_AG_RESV_METADATA:
406 case XFS_AG_RESV_RMAPBT:
407 resv = xfs_perag_resv(pag, type: type);
408 break;
409 default:
410 ASSERT(0);
411 fallthrough;
412 case XFS_AG_RESV_NONE:
413 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
414 fallthrough;
415 case XFS_AG_RESV_IGNORE:
416 return;
417 }
418
419 leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
420 resv->ar_reserved += leftover;
421 if (type == XFS_AG_RESV_RMAPBT)
422 return;
423 /* Freeing into the reserved pool only requires on-disk update... */
424 xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
425 /* ...but freeing beyond that requires in-core and on-disk update. */
426 if (len > leftover)
427 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
428}
429

source code of linux/fs/xfs/libxfs/xfs_ag_resv.c