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 "libxfs_priv.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_sb.h"
  13 #include "xfs_mount.h"
  14 #include "xfs_defer.h"
  15 #include "xfs_alloc.h"
  16 #include "xfs_errortag.h"
  17 #include "xfs_trace.h"
  18 #include "xfs_cksum.h"
  19 #include "xfs_trans.h"
  20 #include "xfs_bit.h"
  21 #include "xfs_bmap.h"
  22 #include "xfs_bmap_btree.h"
  23 #include "xfs_ag_resv.h"
  24 #include "xfs_trans_space.h"
  25 #include "xfs_rmap_btree.h"
  26 #include "xfs_btree.h"
  27 #include "xfs_refcount_btree.h"
  28 #include "xfs_ialloc_btree.h"
  29
  30 /*
  31  * Per-AG Block Reservations
  32  *
  33  * For some kinds of allocation group metadata structures, it is advantageous
  34  * to reserve a small number of blocks in each AG so that future expansions of
  35  * that data structure do not encounter ENOSPC because errors during a btree
  36  * split cause the filesystem to go offline.
  37  *
  38  * Prior to the introduction of reflink, this wasn't an issue because the free
  39  * space btrees maintain a reserve of space (the AGFL) to handle any expansion
  40  * that may be necessary; and allocations of other metadata (inodes, BMBT,
  41  * dir/attr) aren't restricted to a single AG.  However, with reflink it is
  42  * possible to allocate all the space in an AG, have subsequent reflink/CoW
  43  * activity expand the refcount btree, and discover that there's no space left
  44  * to handle that expansion.  Since we can calculate the maximum size of the
  45  * refcount btree, we can reserve space for it and avoid ENOSPC.
  46  *
  47  * Handling per-AG reservations consists of three changes to the allocator's
  48  * behavior:  First, because these reservations are always needed, we decrease
  49  * the ag_max_usable counter to reflect the size of the AG after the reserved
  50  * blocks are taken.  Second, the reservations must be reflected in the
  51  * fdblocks count to maintain proper accounting.  Third, each AG must maintain
  52  * its own reserved block counter so that we can calculate the amount of space
  53  * that must remain free to maintain the reservations.  Fourth, the "remaining
  54  * reserved blocks" count must be used when calculating the length of the
  55  * longest free extent in an AG and to clamp maxlen in the per-AG allocation
  56  * functions.  In other words, we maintain a virtual allocation via in-core
  57  * accounting tricks so that we don't have to clean up after a crash. :)
  58  *
  59  * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
  60  * values via struct xfs_alloc_arg or directly to the xfs_free_extent
  61  * function.  It might seem a little funny to maintain a reservoir of blocks
  62  * to feed another reservoir, but the AGFL only holds enough blocks to get
  63  * through the next transaction.  The per-AG reservation is to ensure (we
  64  * hope) that each AG never runs out of blocks.  Each data structure wanting
  65  * to use the reservation system should update ask/used in xfs_ag_resv_init.
  66  */
  67
  68 /*
  69  * Are we critically low on blocks?  For now we'll define that as the number
  70  * of blocks we can get our hands on being less than 10% of what we reserved
  71  * or less than some arbitrary number (maximum btree height).
  72  */
  73 bool
  74 xfs_ag_resv_critical(
  75         struct xfs_perag                *pag,
  76         enum xfs_ag_resv_type           type)
  77 {
  78         xfs_extlen_t                    avail;
  79         xfs_extlen_t                    orig;
  80
  81         switch (type) {
  82         case XFS_AG_RESV_METADATA:
  83                 avail = pag->pagf_freeblks - pag->pag_rmapbt_resv.ar_reserved;
  84                 orig = pag->pag_meta_resv.ar_asked;
  85                 break;
  86         case XFS_AG_RESV_RMAPBT:
  87                 avail = pag->pagf_freeblks + pag->pagf_flcount -
  88                         pag->pag_meta_resv.ar_reserved;
  89                 orig = pag->pag_rmapbt_resv.ar_asked;
  90                 break;
  91         default:
  92                 ASSERT(0);
  93                 return false;
  94         }
  95
  96         trace_xfs_ag_resv_critical(pag, type, avail);
  97
  98         /* Critically low if less than 10% or max btree height remains. */
  99         return XFS_TEST_ERROR(avail < orig / 10 || avail < XFS_BTREE_MAXLEVELS,
 100                         pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL);
 101 }
 102
 103 /*
 104  * How many blocks are reserved but not used, and therefore must not be
 105  * allocated away?
 106  */
 107 xfs_extlen_t
 108 xfs_ag_resv_needed(
 109         struct xfs_perag                *pag,
 110         enum xfs_ag_resv_type           type)
 111 {
 112         xfs_extlen_t                    len;
 113
 114         len = pag->pag_meta_resv.ar_reserved + pag->pag_rmapbt_resv.ar_reserved;
 115         switch (type) {
 116         case XFS_AG_RESV_METADATA:
 117         case XFS_AG_RESV_RMAPBT:
 118                 len -= xfs_perag_resv(pag, type)->ar_reserved;
 119                 break;
 120         case XFS_AG_RESV_NONE:
 121                 /* empty */
 122                 break;
 123         default:
 124                 ASSERT(0);
 125         }
 126
 127         trace_xfs_ag_resv_needed(pag, type, len);
 128
 129         return len;
 130 }
 131
 132 /* Clean out a reservation */
 133 static int
 134 __xfs_ag_resv_free(
 135         struct xfs_perag                *pag,
 136         enum xfs_ag_resv_type           type)
 137 {
 138         struct xfs_ag_resv              *resv;
 139         xfs_extlen_t                    oldresv;
 140         int                             error;
 141
 142         trace_xfs_ag_resv_free(pag, type, 0);
 143
 144         resv = xfs_perag_resv(pag, type);
 145         if (pag->pag_agno == 0)
 146                 pag->pag_mount->m_ag_max_usable += resv->ar_asked;
 147         /*
 148          * RMAPBT blocks come from the AGFL and AGFL blocks are always
 149          * considered "free", so whatever was reserved at mount time must be
 150          * given back at umount.
 151          */
 152         if (type == XFS_AG_RESV_RMAPBT)
 153                 oldresv = resv->ar_orig_reserved;
 154         else
 155                 oldresv = resv->ar_reserved;
 156         error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
 157         resv->ar_reserved = 0;
 158         resv->ar_asked = 0;
 159         resv->ar_orig_reserved = 0;
 160
 161         if (error)
 162                 trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
 163                                 error, _RET_IP_);
 164         return error;
 165 }
 166
 167 /* Free a per-AG reservation. */
 168 int
 169 xfs_ag_resv_free(
 170         struct xfs_perag                *pag)
 171 {
 172         int                             error;
 173         int                             err2;
 174
 175         error = __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
 176         err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
 177         if (err2 && !error)
 178                 error = err2;
 179         return error;
 180 }
 181
 182 static int
 183 __xfs_ag_resv_init(
 184         struct xfs_perag                *pag,
 185         enum xfs_ag_resv_type           type,
 186         xfs_extlen_t                    ask,
 187         xfs_extlen_t                    used)
 188 {
 189         struct xfs_mount                *mp = pag->pag_mount;
 190         struct xfs_ag_resv              *resv;
 191         int                             error;
 192         xfs_extlen_t                    hidden_space;
 193
 194         if (used > ask)
 195                 ask = used;
 196
 197         switch (type) {
 198         case XFS_AG_RESV_RMAPBT:
 199                 /*
 200                  * Space taken by the rmapbt is not subtracted from fdblocks
 201                  * because the rmapbt lives in the free space.  Here we must
 202                  * subtract the entire reservation from fdblocks so that we
 203                  * always have blocks available for rmapbt expansion.
 204                  */
 205                 hidden_space = ask;
 206                 break;
 207         case XFS_AG_RESV_METADATA:
 208                 /*
 209                  * Space taken by all other metadata btrees are accounted
 210                  * on-disk as used space.  We therefore only hide the space
 211                  * that is reserved but not used by the trees.
 212                  */
 213                 hidden_space = ask - used;
 214                 break;
 215         default:
 216                 ASSERT(0);
 217                 return -EINVAL;
 218         }
 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);
 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. */
 248 int
 249 xfs_ag_resv_init(
 250         struct xfs_perag                *pag,
 251         struct xfs_trans                *tp)
 252 {
 253         struct xfs_mount                *mp = pag->pag_mount;
 254         xfs_agnumber_t                  agno = pag->pag_agno;
 255         xfs_extlen_t                    ask;
 256         xfs_extlen_t                    used;
 257         int                             error = 0;
 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, agno, &ask, &used);
 264                 if (error)
 265                         goto out;
 266
 267                 error = xfs_finobt_calc_reserves(mp, tp, agno, &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_inotbt_nores = true;
 284
 285                         error = xfs_refcountbt_calc_reserves(mp, tp, agno, &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         }
 296
 297         /* Create the RMAPBT metadata reservation */
 298         if (pag->pag_rmapbt_resv.ar_asked == 0) {
 299                 ask = used = 0;
 300
 301                 error = xfs_rmapbt_calc_reserves(mp, tp, agno, &ask, &used);
 302                 if (error)
 303                         goto out;
 304
 305                 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
 306                 if (error)
 307                         goto out;
 308         }
 309
 310 #ifdef DEBUG
 311         /* need to read in the AGF for the ASSERT below to work */
 312         error = xfs_alloc_pagf_init(pag->pag_mount, tp, pag->pag_agno, 0);
 313         if (error)
 314                 return error;
 315
 316         ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
 317                xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <=
 318                pag->pagf_freeblks + pag->pagf_flcount);
 319 #endif
 320 out:
 321         return error;
 322 }
 323
 324 /* Allocate a block from the reservation. */
 325 void
 326 xfs_ag_resv_alloc_extent(
 327         struct xfs_perag                *pag,
 328         enum xfs_ag_resv_type           type,
 329         struct xfs_alloc_arg            *args)
 330 {
 331         struct xfs_ag_resv              *resv;
 332         xfs_extlen_t                    len;
 333         uint                            field;
 334
 335         trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
 336
 337         switch (type) {
 338         case XFS_AG_RESV_AGFL:
 339                 return;
 340         case XFS_AG_RESV_METADATA:
 341         case XFS_AG_RESV_RMAPBT:
 342                 resv = xfs_perag_resv(pag, type);
 343                 break;
 344         default:
 345                 ASSERT(0);
 346                 /* fall through */
 347         case XFS_AG_RESV_NONE:
 348                 field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
 349                                        XFS_TRANS_SB_FDBLOCKS;
 350                 xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
 351                 return;
 352         }
 353
 354         len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
 355         resv->ar_reserved -= len;
 356         if (type == XFS_AG_RESV_RMAPBT)
 357                 return;
 358         /* Allocations of reserved blocks only need on-disk sb updates... */
 359         xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
 360         /* ...but non-reserved blocks need in-core and on-disk updates. */
 361         if (args->len > len)
 362                 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
 363                                 -((int64_t)args->len - len));
 364 }
 365
 366 /* Free a block to the reservation. */
 367 void
 368 xfs_ag_resv_free_extent(
 369         struct xfs_perag                *pag,
 370         enum xfs_ag_resv_type           type,
 371         struct xfs_trans                *tp,
 372         xfs_extlen_t                    len)
 373 {
 374         xfs_extlen_t                    leftover;
 375         struct xfs_ag_resv              *resv;
 376
 377         trace_xfs_ag_resv_free_extent(pag, type, len);
 378
 379         switch (type) {
 380         case XFS_AG_RESV_AGFL:
 381                 return;
 382         case XFS_AG_RESV_METADATA:
 383         case XFS_AG_RESV_RMAPBT:
 384                 resv = xfs_perag_resv(pag, type);
 385                 break;
 386         default:
 387                 ASSERT(0);
 388                 /* fall through */
 389         case XFS_AG_RESV_NONE:
 390                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
 391                 return;
 392         }
 393
 394         leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
 395         resv->ar_reserved += leftover;
 396         if (type == XFS_AG_RESV_RMAPBT)
 397                 return;
 398         /* Freeing into the reserved pool only requires on-disk update... */
 399         xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
 400         /* ...but freeing beyond that requires in-core and on-disk update. */
 401         if (len > leftover)
 402                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
 403 }