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_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_error.h"
  18 #include "xfs_trace.h"
  19 #include "xfs_cksum.h"
  20 #include "xfs_trans.h"
  21 #include "xfs_bit.h"
  22 #include "xfs_bmap.h"
  23 #include "xfs_bmap_btree.h"
  24 #include "xfs_ag_resv.h"
  25 #include "xfs_trans_space.h"
  26 #include "xfs_rmap_btree.h"
  27 #include "xfs_btree.h"
  28 #include "xfs_refcount_btree.h"
  29 #include "xfs_ialloc_btree.h"
  30
  31 /*
  32  * Per-AG Block Reservations
  33  *
  34  * For some kinds of allocation group metadata structures, it is advantageous
  35  * to reserve a small number of blocks in each AG so that future expansions of
  36  * that data structure do not encounter ENOSPC because errors during a btree
  37  * split cause the filesystem to go offline.
  38  *
  39  * Prior to the introduction of reflink, this wasn't an issue because the free
  40  * space btrees maintain a reserve of space (the AGFL) to handle any expansion
  41  * that may be necessary; and allocations of other metadata (inodes, BMBT,
  42  * dir/attr) aren't restricted to a single AG.  However, with reflink it is
  43  * possible to allocate all the space in an AG, have subsequent reflink/CoW
  44  * activity expand the refcount btree, and discover that there's no space left
  45  * to handle that expansion.  Since we can calculate the maximum size of the
  46  * refcount btree, we can reserve space for it and avoid ENOSPC.
  47  *
  48  * Handling per-AG reservations consists of three changes to the allocator's
  49  * behavior:  First, because these reservations are always needed, we decrease
  50  * the ag_max_usable counter to reflect the size of the AG after the reserved
  51  * blocks are taken.  Second, the reservations must be reflected in the
  52  * fdblocks count to maintain proper accounting.  Third, each AG must maintain
  53  * its own reserved block counter so that we can calculate the amount of space
  54  * that must remain free to maintain the reservations.  Fourth, the "remaining
  55  * reserved blocks" count must be used when calculating the length of the
  56  * longest free extent in an AG and to clamp maxlen in the per-AG allocation
  57  * functions.  In other words, we maintain a virtual allocation via in-core
  58  * accounting tricks so that we don't have to clean up after a crash. :)
  59  *
  60  * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
  61  * values via struct xfs_alloc_arg or directly to the xfs_free_extent
  62  * function.  It might seem a little funny to maintain a reservoir of blocks
  63  * to feed another reservoir, but the AGFL only holds enough blocks to get
  64  * through the next transaction.  The per-AG reservation is to ensure (we
  65  * hope) that each AG never runs out of blocks.  Each data structure wanting
  66  * to use the reservation system should update ask/used in xfs_ag_resv_init.
  67  */
  68
  69 /*
  70  * Are we critically low on blocks?  For now we'll define that as the number
  71  * of blocks we can get our hands on being less than 10% of what we reserved
  72  * or less than some arbitrary number (maximum btree height).
  73  */
  74 bool
  75 xfs_ag_resv_critical(
  76         struct xfs_perag                *pag,
  77         enum xfs_ag_resv_type           type)
  78 {
  79         xfs_extlen_t                    avail;
  80         xfs_extlen_t                    orig;
  81
  82         switch (type) {
  83         case XFS_AG_RESV_METADATA:
  84                 avail = pag->pagf_freeblks - pag->pag_rmapbt_resv.ar_reserved;
  85                 orig = pag->pag_meta_resv.ar_asked;
  86                 break;
  87         case XFS_AG_RESV_RMAPBT:
  88                 avail = pag->pagf_freeblks + pag->pagf_flcount -
  89                         pag->pag_meta_resv.ar_reserved;
  90                 orig = pag->pag_rmapbt_resv.ar_asked;
  91                 break;
  92         default:
  93                 ASSERT(0);
  94                 return false;
  95         }
  96
  97         trace_xfs_ag_resv_critical(pag, type, avail);
  98
  99         /* Critically low if less than 10% or max btree height remains. */
 100         return XFS_TEST_ERROR(avail < orig / 10 || avail < XFS_BTREE_MAXLEVELS,
 101                         pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL);
 102 }
 103
 104 /*
 105  * How many blocks are reserved but not used, and therefore must not be
 106  * allocated away?
 107  */
 108 xfs_extlen_t
 109 xfs_ag_resv_needed(
 110         struct xfs_perag                *pag,
 111         enum xfs_ag_resv_type           type)
 112 {
 113         xfs_extlen_t                    len;
 114
 115         len = pag->pag_meta_resv.ar_reserved + pag->pag_rmapbt_resv.ar_reserved;
 116         switch (type) {
 117         case XFS_AG_RESV_METADATA:
 118         case XFS_AG_RESV_RMAPBT:
 119                 len -= xfs_perag_resv(pag, type)->ar_reserved;
 120                 break;
 121         case XFS_AG_RESV_NONE:
 122                 /* empty */
 123                 break;
 124         default:
 125                 ASSERT(0);
 126         }
 127
 128         trace_xfs_ag_resv_needed(pag, type, len);
 129
 130         return len;
 131 }
 132
 133 /* Clean out a reservation */
 134 static int
 135 __xfs_ag_resv_free(
 136         struct xfs_perag                *pag,
 137         enum xfs_ag_resv_type           type)
 138 {
 139         struct xfs_ag_resv              *resv;
 140         xfs_extlen_t                    oldresv;
 141         int                             error;
 142
 143         trace_xfs_ag_resv_free(pag, type, 0);
 144
 145         resv = xfs_perag_resv(pag, type);
 146         if (pag->pag_agno == 0)
 147                 pag->pag_mount->m_ag_max_usable += resv->ar_asked;
 148         /*
 149          * RMAPBT blocks come from the AGFL and AGFL blocks are always
 150          * considered "free", so whatever was reserved at mount time must be
 151          * given back at umount.
 152          */
 153         if (type == XFS_AG_RESV_RMAPBT)
 154                 oldresv = resv->ar_orig_reserved;
 155         else
 156                 oldresv = resv->ar_reserved;
 157         error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
 158         resv->ar_reserved = 0;
 159         resv->ar_asked = 0;
 160         resv->ar_orig_reserved = 0;
 161
 162         if (error)
 163                 trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
 164                                 error, _RET_IP_);
 165         return error;
 166 }
 167
 168 /* Free a per-AG reservation. */
 169 int
 170 xfs_ag_resv_free(
 171         struct xfs_perag                *pag)
 172 {
 173         int                             error;
 174         int                             err2;
 175
 176         error = __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
 177         err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
 178         if (err2 && !error)
 179                 error = err2;
 180         return error;
 181 }
 182
 183 static int
 184 __xfs_ag_resv_init(
 185         struct xfs_perag                *pag,
 186         enum xfs_ag_resv_type           type,
 187         xfs_extlen_t                    ask,
 188         xfs_extlen_t                    used)
 189 {
 190         struct xfs_mount                *mp = pag->pag_mount;
 191         struct xfs_ag_resv              *resv;
 192         int                             error;
 193         xfs_extlen_t                    hidden_space;
 194
 195         if (used > ask)
 196                 ask = used;
 197
 198         switch (type) {
 199         case XFS_AG_RESV_RMAPBT:
 200                 /*
 201                  * Space taken by the rmapbt is not subtracted from fdblocks
 202                  * because the rmapbt lives in the free space.  Here we must
 203                  * subtract the entire reservation from fdblocks so that we
 204                  * always have blocks available for rmapbt expansion.
 205                  */
 206                 hidden_space = ask;
 207                 break;
 208         case XFS_AG_RESV_METADATA:
 209                 /*
 210                  * Space taken by all other metadata btrees are accounted
 211                  * on-disk as used space.  We therefore only hide the space
 212                  * that is reserved but not used by the trees.
 213                  */
 214                 hidden_space = ask - used;
 215                 break;
 216         default:
 217                 ASSERT(0);
 218                 return -EINVAL;
 219         }
 220         error = xfs_mod_fdblocks(mp, -(int64_t)hidden_space, true);
 221         if (error) {
 222                 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
 223                                 error, _RET_IP_);
 224                 xfs_warn(mp,
 225 "Per-AG reservation for AG %u failed.  Filesystem may run out of space.",
 226                                 pag->pag_agno);
 227                 return error;
 228         }
 229
 230         /*
 231          * Reduce the maximum per-AG allocation length by however much we're
 232          * trying to reserve for an AG.  Since this is a filesystem-wide
 233          * counter, we only make the adjustment for AG 0.  This assumes that
 234          * there aren't any AGs hungrier for per-AG reservation than AG 0.
 235          */
 236         if (pag->pag_agno == 0)
 237                 mp->m_ag_max_usable -= ask;
 238
 239         resv = xfs_perag_resv(pag, type);
 240         resv->ar_asked = ask;
 241         resv->ar_orig_reserved = hidden_space;
 242         resv->ar_reserved = ask - used;
 243
 244         trace_xfs_ag_resv_init(pag, type, ask);
 245         return 0;
 246 }
 247
 248 /* Create a per-AG block reservation. */
 249 int
 250 xfs_ag_resv_init(
 251         struct xfs_perag                *pag,
 252         struct xfs_trans                *tp)
 253 {
 254         struct xfs_mount                *mp = pag->pag_mount;
 255         xfs_agnumber_t                  agno = pag->pag_agno;
 256         xfs_extlen_t                    ask;
 257         xfs_extlen_t                    used;
 258         int                             error = 0;
 259
 260         /* Create the metadata reservation. */
 261         if (pag->pag_meta_resv.ar_asked == 0) {
 262                 ask = used = 0;
 263
 264                 error = xfs_refcountbt_calc_reserves(mp, tp, agno, &ask, &used);
 265                 if (error)
 266                         goto out;
 267
 268                 error = xfs_finobt_calc_reserves(mp, tp, agno, &ask, &used);
 269                 if (error)
 270                         goto out;
 271
 272                 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
 273                                 ask, used);
 274                 if (error) {
 275                         /*
 276                          * Because we didn't have per-AG reservations when the
 277                          * finobt feature was added we might not be able to
 278                          * reserve all needed blocks.  Warn and fall back to the
 279                          * old and potentially buggy code in that case, but
 280                          * ensure we do have the reservation for the refcountbt.
 281                          */
 282                         ask = used = 0;
 283
 284                         mp->m_inotbt_nores = true;
 285
 286                         error = xfs_refcountbt_calc_reserves(mp, tp, agno, &ask,
 287                                         &used);
 288                         if (error)
 289                                 goto out;
 290
 291                         error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
 292                                         ask, used);
 293                         if (error)
 294                                 goto out;
 295                 }
 296         }
 297
 298         /* Create the RMAPBT metadata reservation */
 299         if (pag->pag_rmapbt_resv.ar_asked == 0) {
 300                 ask = used = 0;
 301
 302                 error = xfs_rmapbt_calc_reserves(mp, tp, agno, &ask, &used);
 303                 if (error)
 304                         goto out;
 305
 306                 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
 307                 if (error)
 308                         goto out;
 309         }
 310
 311 #ifdef DEBUG
 312         /* need to read in the AGF for the ASSERT below to work */
 313         error = xfs_alloc_pagf_init(pag->pag_mount, tp, pag->pag_agno, 0);
 314         if (error)
 315                 return error;
 316
 317         ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
 318                xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <=
 319                pag->pagf_freeblks + pag->pagf_flcount);
 320 #endif
 321 out:
 322         return error;
 323 }
 324
 325 /* Allocate a block from the reservation. */
 326 void
 327 xfs_ag_resv_alloc_extent(
 328         struct xfs_perag                *pag,
 329         enum xfs_ag_resv_type           type,
 330         struct xfs_alloc_arg            *args)
 331 {
 332         struct xfs_ag_resv              *resv;
 333         xfs_extlen_t                    len;
 334         uint                            field;
 335
 336         trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
 337
 338         switch (type) {
 339         case XFS_AG_RESV_AGFL:
 340                 return;
 341         case XFS_AG_RESV_METADATA:
 342         case XFS_AG_RESV_RMAPBT:
 343                 resv = xfs_perag_resv(pag, type);
 344                 break;
 345         default:
 346                 ASSERT(0);
 347                 /* fall through */
 348         case XFS_AG_RESV_NONE:
 349                 field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
 350                                        XFS_TRANS_SB_FDBLOCKS;
 351                 xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
 352                 return;
 353         }
 354
 355         len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
 356         resv->ar_reserved -= len;
 357         if (type == XFS_AG_RESV_RMAPBT)
 358                 return;
 359         /* Allocations of reserved blocks only need on-disk sb updates... */
 360         xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
 361         /* ...but non-reserved blocks need in-core and on-disk updates. */
 362         if (args->len > len)
 363                 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
 364                                 -((int64_t)args->len - len));
 365 }
 366
 367 /* Free a block to the reservation. */
 368 void
 369 xfs_ag_resv_free_extent(
 370         struct xfs_perag                *pag,
 371         enum xfs_ag_resv_type           type,
 372         struct xfs_trans                *tp,
 373         xfs_extlen_t                    len)
 374 {
 375         xfs_extlen_t                    leftover;
 376         struct xfs_ag_resv              *resv;
 377
 378         trace_xfs_ag_resv_free_extent(pag, type, len);
 379
 380         switch (type) {
 381         case XFS_AG_RESV_AGFL:
 382                 return;
 383         case XFS_AG_RESV_METADATA:
 384         case XFS_AG_RESV_RMAPBT:
 385                 resv = xfs_perag_resv(pag, type);
 386                 break;
 387         default:
 388                 ASSERT(0);
 389                 /* fall through */
 390         case XFS_AG_RESV_NONE:
 391                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
 392                 return;
 393         }
 394
 395         leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
 396         resv->ar_reserved += leftover;
 397         if (type == XFS_AG_RESV_RMAPBT)
 398                 return;
 399         /* Freeing into the reserved pool only requires on-disk update... */
 400         xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
 401         /* ...but freeing beyond that requires in-core and on-disk update. */
 402         if (len > leftover)
 403                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
 404 }