fs/xfs/libxfs/xfs_ag_resv.c

   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         struct xfs_mount                *mp = pag_mount(pag);
  74         xfs_extlen_t                    avail;
  75         xfs_extlen_t                    orig;
  76
  77         switch (type) {
  78         case XFS_AG_RESV_METADATA:
  79                 avail = pag->pagf_freeblks - pag->pag_rmapbt_resv.ar_reserved;
  80                 orig = pag->pag_meta_resv.ar_asked;
  81                 break;
  82         case XFS_AG_RESV_RMAPBT:
  83                 avail = pag->pagf_freeblks + pag->pagf_flcount -
  84                         pag->pag_meta_resv.ar_reserved;
  85                 orig = pag->pag_rmapbt_resv.ar_asked;
  86                 break;
  87         default:
  88                 ASSERT(0);
  89                 return false;
  90         }
  91
  92         trace_xfs_ag_resv_critical(pag, type, avail);
  93
  94         /* Critically low if less than 10% or max btree height remains. */
  95         return XFS_TEST_ERROR(avail < orig / 10 ||
  96                               avail < mp->m_agbtree_maxlevels,
  97                         mp, XFS_ERRTAG_AG_RESV_CRITICAL);
  98 }
  99
 100 /*
 101  * How many blocks are reserved but not used, and therefore must not be
 102  * allocated away?
 103  */
 104 xfs_extlen_t
 105 xfs_ag_resv_needed(
 106         struct xfs_perag                *pag,
 107         enum xfs_ag_resv_type           type)
 108 {
 109         xfs_extlen_t                    len;
 110
 111         len = pag->pag_meta_resv.ar_reserved + pag->pag_rmapbt_resv.ar_reserved;
 112         switch (type) {
 113         case XFS_AG_RESV_METADATA:
 114         case XFS_AG_RESV_RMAPBT:
 115                 len -= xfs_perag_resv(pag, type)->ar_reserved;
 116                 break;
 117         case XFS_AG_RESV_NONE:
 118                 /* empty */
 119                 break;
 120         default:
 121                 ASSERT(0);
 122         }
 123
 124         trace_xfs_ag_resv_needed(pag, type, len);
 125
 126         return len;
 127 }
 128
 129 /* Clean out a reservation */
 130 static void
 131 __xfs_ag_resv_free(
 132         struct xfs_perag                *pag,
 133         enum xfs_ag_resv_type           type)
 134 {
 135         struct xfs_ag_resv              *resv;
 136         xfs_extlen_t                    oldresv;
 137
 138         trace_xfs_ag_resv_free(pag, type, 0);
 139
 140         resv = xfs_perag_resv(pag, type);
 141         if (pag_agno(pag) == 0)
 142                 pag_mount(pag)->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         xfs_add_fdblocks(pag_mount(pag), oldresv);
 153         resv->ar_reserved = 0;
 154         resv->ar_asked = 0;
 155         resv->ar_orig_reserved = 0;
 156 }
 157
 158 /* Free a per-AG reservation. */
 159 void
 160 xfs_ag_resv_free(
 161         struct xfs_perag                *pag)
 162 {
 163         __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
 164         __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
 165 }
 166
 167 static int
 168 __xfs_ag_resv_init(
 169         struct xfs_perag                *pag,
 170         enum xfs_ag_resv_type           type,
 171         xfs_extlen_t                    ask,
 172         xfs_extlen_t                    used)
 173 {
 174         struct xfs_mount                *mp = pag_mount(pag);
 175         struct xfs_ag_resv              *resv;
 176         int                             error;
 177         xfs_extlen_t                    hidden_space;
 178
 179         if (used > ask)
 180                 ask = used;
 181
 182         switch (type) {
 183         case XFS_AG_RESV_RMAPBT:
 184                 /*
 185                  * Space taken by the rmapbt is not subtracted from fdblocks
 186                  * because the rmapbt lives in the free space.  Here we must
 187                  * subtract the entire reservation from fdblocks so that we
 188                  * always have blocks available for rmapbt expansion.
 189                  */
 190                 hidden_space = ask;
 191                 break;
 192         case XFS_AG_RESV_METADATA:
 193                 /*
 194                  * Space taken by all other metadata btrees are accounted
 195                  * on-disk as used space.  We therefore only hide the space
 196                  * that is reserved but not used by the trees.
 197                  */
 198                 hidden_space = ask - used;
 199                 break;
 200         default:
 201                 ASSERT(0);
 202                 return -EINVAL;
 203         }
 204
 205         if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
 206                 error = -ENOSPC;
 207         else
 208                 error = xfs_dec_fdblocks(mp, hidden_space, true);
 209         if (error) {
 210                 trace_xfs_ag_resv_init_error(pag, error, _RET_IP_);
 211                 xfs_warn(mp,
 212 "Per-AG reservation for AG %u failed.  Filesystem may run out of space.",
 213                                 pag_agno(pag));
 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_agno(pag) == 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_mount(pag);
 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 }