fs/xfs/libxfs/xfs_ag_resv.c

   1 /*
   2  * Copyright (C) 2016 Oracle.  All Rights Reserved.
   3  *
   4  * Author: Darrick J. Wong <darrick.wong@oracle.com>
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version 2
   9  * of the License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it would be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write the Free Software Foundation,
  18  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
  19  */
  20 #include "xfs.h"
  21 #include "xfs_fs.h"
  22 #include "xfs_shared.h"
  23 #include "xfs_format.h"
  24 #include "xfs_log_format.h"
  25 #include "xfs_trans_resv.h"
  26 #include "xfs_sb.h"
  27 #include "xfs_mount.h"
  28 #include "xfs_defer.h"
  29 #include "xfs_alloc.h"
  30 #include "xfs_error.h"
  31 #include "xfs_trace.h"
  32 #include "xfs_cksum.h"
  33 #include "xfs_trans.h"
  34 #include "xfs_bit.h"
  35 #include "xfs_bmap.h"
  36 #include "xfs_bmap_btree.h"
  37 #include "xfs_ag_resv.h"
  38 #include "xfs_trans_space.h"
  39 #include "xfs_rmap_btree.h"
  40 #include "xfs_btree.h"
  41 #include "xfs_refcount_btree.h"
  42 #include "xfs_ialloc_btree.h"
  43
  44 /*
  45  * Per-AG Block Reservations
  46  *
  47  * For some kinds of allocation group metadata structures, it is advantageous
  48  * to reserve a small number of blocks in each AG so that future expansions of
  49  * that data structure do not encounter ENOSPC because errors during a btree
  50  * split cause the filesystem to go offline.
  51  *
  52  * Prior to the introduction of reflink, this wasn't an issue because the free
  53  * space btrees maintain a reserve of space (the AGFL) to handle any expansion
  54  * that may be necessary; and allocations of other metadata (inodes, BMBT,
  55  * dir/attr) aren't restricted to a single AG.  However, with reflink it is
  56  * possible to allocate all the space in an AG, have subsequent reflink/CoW
  57  * activity expand the refcount btree, and discover that there's no space left
  58  * to handle that expansion.  Since we can calculate the maximum size of the
  59  * refcount btree, we can reserve space for it and avoid ENOSPC.
  60  *
  61  * Handling per-AG reservations consists of three changes to the allocator's
  62  * behavior:  First, because these reservations are always needed, we decrease
  63  * the ag_max_usable counter to reflect the size of the AG after the reserved
  64  * blocks are taken.  Second, the reservations must be reflected in the
  65  * fdblocks count to maintain proper accounting.  Third, each AG must maintain
  66  * its own reserved block counter so that we can calculate the amount of space
  67  * that must remain free to maintain the reservations.  Fourth, the "remaining
  68  * reserved blocks" count must be used when calculating the length of the
  69  * longest free extent in an AG and to clamp maxlen in the per-AG allocation
  70  * functions.  In other words, we maintain a virtual allocation via in-core
  71  * accounting tricks so that we don't have to clean up after a crash. :)
  72  *
  73  * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
  74  * values via struct xfs_alloc_arg or directly to the xfs_free_extent
  75  * function.  It might seem a little funny to maintain a reservoir of blocks
  76  * to feed another reservoir, but the AGFL only holds enough blocks to get
  77  * through the next transaction.  The per-AG reservation is to ensure (we
  78  * hope) that each AG never runs out of blocks.  Each data structure wanting
  79  * to use the reservation system should update ask/used in xfs_ag_resv_init.
  80  */
  81
  82 /*
  83  * Are we critically low on blocks?  For now we'll define that as the number
  84  * of blocks we can get our hands on being less than 10% of what we reserved
  85  * or less than some arbitrary number (maximum btree height).
  86  */
  87 bool
  88 xfs_ag_resv_critical(
  89         struct xfs_perag                *pag,
  90         enum xfs_ag_resv_type           type)
  91 {
  92         xfs_extlen_t                    avail;
  93         xfs_extlen_t                    orig;
  94
  95         switch (type) {
  96         case XFS_AG_RESV_METADATA:
  97                 avail = pag->pagf_freeblks - pag->pag_agfl_resv.ar_reserved;
  98                 orig = pag->pag_meta_resv.ar_asked;
  99                 break;
 100         case XFS_AG_RESV_AGFL:
 101                 avail = pag->pagf_freeblks + pag->pagf_flcount -
 102                         pag->pag_meta_resv.ar_reserved;
 103                 orig = pag->pag_agfl_resv.ar_asked;
 104                 break;
 105         default:
 106                 ASSERT(0);
 107                 return false;
 108         }
 109
 110         trace_xfs_ag_resv_critical(pag, type, avail);
 111
 112         /* Critically low if less than 10% or max btree height remains. */
 113         return XFS_TEST_ERROR(avail < orig / 10 || avail < XFS_BTREE_MAXLEVELS,
 114                         pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL);
 115 }
 116
 117 /*
 118  * How many blocks are reserved but not used, and therefore must not be
 119  * allocated away?
 120  */
 121 xfs_extlen_t
 122 xfs_ag_resv_needed(
 123         struct xfs_perag                *pag,
 124         enum xfs_ag_resv_type           type)
 125 {
 126         xfs_extlen_t                    len;
 127
 128         len = pag->pag_meta_resv.ar_reserved + pag->pag_agfl_resv.ar_reserved;
 129         switch (type) {
 130         case XFS_AG_RESV_METADATA:
 131         case XFS_AG_RESV_AGFL:
 132                 len -= xfs_perag_resv(pag, type)->ar_reserved;
 133                 break;
 134         case XFS_AG_RESV_NONE:
 135                 /* empty */
 136                 break;
 137         default:
 138                 ASSERT(0);
 139         }
 140
 141         trace_xfs_ag_resv_needed(pag, type, len);
 142
 143         return len;
 144 }
 145
 146 /* Clean out a reservation */
 147 static int
 148 __xfs_ag_resv_free(
 149         struct xfs_perag                *pag,
 150         enum xfs_ag_resv_type           type)
 151 {
 152         struct xfs_ag_resv              *resv;
 153         xfs_extlen_t                    oldresv;
 154         int                             error;
 155
 156         trace_xfs_ag_resv_free(pag, type, 0);
 157
 158         resv = xfs_perag_resv(pag, type);
 159         if (pag->pag_agno == 0)
 160                 pag->pag_mount->m_ag_max_usable += resv->ar_asked;
 161         /*
 162          * AGFL blocks are always considered "free", so whatever
 163          * was reserved at mount time must be given back at umount.
 164          */
 165         if (type == XFS_AG_RESV_AGFL)
 166                 oldresv = resv->ar_orig_reserved;
 167         else
 168                 oldresv = resv->ar_reserved;
 169         error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
 170         resv->ar_reserved = 0;
 171         resv->ar_asked = 0;
 172
 173         if (error)
 174                 trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
 175                                 error, _RET_IP_);
 176         return error;
 177 }
 178
 179 /* Free a per-AG reservation. */
 180 int
 181 xfs_ag_resv_free(
 182         struct xfs_perag                *pag)
 183 {
 184         int                             error;
 185         int                             err2;
 186
 187         error = __xfs_ag_resv_free(pag, XFS_AG_RESV_AGFL);
 188         err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
 189         if (err2 && !error)
 190                 error = err2;
 191         return error;
 192 }
 193
 194 static int
 195 __xfs_ag_resv_init(
 196         struct xfs_perag                *pag,
 197         enum xfs_ag_resv_type           type,
 198         xfs_extlen_t                    ask,
 199         xfs_extlen_t                    used)
 200 {
 201         struct xfs_mount                *mp = pag->pag_mount;
 202         struct xfs_ag_resv              *resv;
 203         int                             error;
 204         xfs_extlen_t                    reserved;
 205
 206         if (used > ask)
 207                 ask = used;
 208         reserved = ask - used;
 209
 210         error = xfs_mod_fdblocks(mp, -(int64_t)reserved, true);
 211         if (error) {
 212                 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
 213                                 error, _RET_IP_);
 214                 xfs_warn(mp,
 215 "Per-AG reservation for AG %u failed.  Filesystem may run out of space.",
 216                                 pag->pag_agno);
 217                 return error;
 218         }
 219
 220         /*
 221          * Reduce the maximum per-AG allocation length by however much we're
 222          * trying to reserve for an AG.  Since this is a filesystem-wide
 223          * counter, we only make the adjustment for AG 0.  This assumes that
 224          * there aren't any AGs hungrier for per-AG reservation than AG 0.
 225          */
 226         if (pag->pag_agno == 0)
 227                 mp->m_ag_max_usable -= ask;
 228
 229         resv = xfs_perag_resv(pag, type);
 230         resv->ar_asked = ask;
 231         resv->ar_reserved = resv->ar_orig_reserved = reserved;
 232
 233         trace_xfs_ag_resv_init(pag, type, ask);
 234         return 0;
 235 }
 236
 237 /* Create a per-AG block reservation. */
 238 int
 239 xfs_ag_resv_init(
 240         struct xfs_perag                *pag)
 241 {
 242         struct xfs_mount                *mp = pag->pag_mount;
 243         xfs_agnumber_t                  agno = pag->pag_agno;
 244         xfs_extlen_t                    ask;
 245         xfs_extlen_t                    used;
 246         int                             error = 0;
 247
 248         /* Create the metadata reservation. */
 249         if (pag->pag_meta_resv.ar_asked == 0) {
 250                 ask = used = 0;
 251
 252                 error = xfs_refcountbt_calc_reserves(mp, agno, &ask, &used);
 253                 if (error)
 254                         goto out;
 255
 256                 error = xfs_finobt_calc_reserves(mp, agno, &ask, &used);
 257                 if (error)
 258                         goto out;
 259
 260                 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
 261                                 ask, used);
 262                 if (error) {
 263                         /*
 264                          * Because we didn't have per-AG reservations when the
 265                          * finobt feature was added we might not be able to
 266                          * reserve all needed blocks.  Warn and fall back to the
 267                          * old and potentially buggy code in that case, but
 268                          * ensure we do have the reservation for the refcountbt.
 269                          */
 270                         ask = used = 0;
 271
 272                         mp->m_inotbt_nores = true;
 273
 274                         error = xfs_refcountbt_calc_reserves(mp, agno, &ask,
 275                                         &used);
 276                         if (error)
 277                                 goto out;
 278
 279                         error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
 280                                         ask, used);
 281                         if (error)
 282                                 goto out;
 283                 }
 284         }
 285
 286         /* Create the AGFL metadata reservation */
 287         if (pag->pag_agfl_resv.ar_asked == 0) {
 288                 ask = used = 0;
 289
 290                 error = xfs_rmapbt_calc_reserves(mp, agno, &ask, &used);
 291                 if (error)
 292                         goto out;
 293
 294                 error = __xfs_ag_resv_init(pag, XFS_AG_RESV_AGFL, ask, used);
 295                 if (error)
 296                         goto out;
 297         }
 298
 299 #ifdef DEBUG
 300         /* need to read in the AGF for the ASSERT below to work */
 301         error = xfs_alloc_pagf_init(pag->pag_mount, NULL, pag->pag_agno, 0);
 302         if (error)
 303                 return error;
 304
 305         ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
 306                xfs_perag_resv(pag, XFS_AG_RESV_AGFL)->ar_reserved <=
 307                pag->pagf_freeblks + pag->pagf_flcount);
 308 #endif
 309 out:
 310         return error;
 311 }
 312
 313 /* Allocate a block from the reservation. */
 314 void
 315 xfs_ag_resv_alloc_extent(
 316         struct xfs_perag                *pag,
 317         enum xfs_ag_resv_type           type,
 318         struct xfs_alloc_arg            *args)
 319 {
 320         struct xfs_ag_resv              *resv;
 321         xfs_extlen_t                    len;
 322         uint                            field;
 323
 324         trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
 325
 326         switch (type) {
 327         case XFS_AG_RESV_METADATA:
 328         case XFS_AG_RESV_AGFL:
 329                 resv = xfs_perag_resv(pag, type);
 330                 break;
 331         default:
 332                 ASSERT(0);
 333                 /* fall through */
 334         case XFS_AG_RESV_NONE:
 335                 field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
 336                                        XFS_TRANS_SB_FDBLOCKS;
 337                 xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
 338                 return;
 339         }
 340
 341         len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
 342         resv->ar_reserved -= len;
 343         if (type == XFS_AG_RESV_AGFL)
 344                 return;
 345         /* Allocations of reserved blocks only need on-disk sb updates... */
 346         xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
 347         /* ...but non-reserved blocks need in-core and on-disk updates. */
 348         if (args->len > len)
 349                 xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
 350                                 -((int64_t)args->len - len));
 351 }
 352
 353 /* Free a block to the reservation. */
 354 void
 355 xfs_ag_resv_free_extent(
 356         struct xfs_perag                *pag,
 357         enum xfs_ag_resv_type           type,
 358         struct xfs_trans                *tp,
 359         xfs_extlen_t                    len)
 360 {
 361         xfs_extlen_t                    leftover;
 362         struct xfs_ag_resv              *resv;
 363
 364         trace_xfs_ag_resv_free_extent(pag, type, len);
 365
 366         switch (type) {
 367         case XFS_AG_RESV_METADATA:
 368         case XFS_AG_RESV_AGFL:
 369                 resv = xfs_perag_resv(pag, type);
 370                 break;
 371         default:
 372                 ASSERT(0);
 373                 /* fall through */
 374         case XFS_AG_RESV_NONE:
 375                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
 376                 return;
 377         }
 378
 379         leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
 380         resv->ar_reserved += leftover;
 381         if (type == XFS_AG_RESV_AGFL)
 382                 return;
 383         /* Freeing into the reserved pool only requires on-disk update... */
 384         xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
 385         /* ...but freeing beyond that requires in-core and on-disk update. */
 386         if (len > leftover)
 387                 xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
 388 }