sys/vfs/hammer/hammer_flusher.c

   1 /*
   2  * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/sys/vfs/hammer/hammer_flusher.c,v 1.45 2008/07/31 04:42:04 dillon Exp $
  35  */
  36 /*
  37  * HAMMER dependancy flusher thread
  38  *
  39  * Meta data updates create buffer dependancies which are arranged as a
  40  * hierarchy of lists.
  41  */
  42
  43 #include "hammer.h"
  44
  45 static void hammer_flusher_master_thread(void *arg);
  46 static void hammer_flusher_slave_thread(void *arg);
  47 static void hammer_flusher_flush(hammer_mount_t hmp);
  48 static void hammer_flusher_flush_inode(hammer_inode_t ip,
  49                                         hammer_transaction_t trans);
  50
  51 RB_GENERATE(hammer_fls_rb_tree, hammer_inode, rb_flsnode,
  52               hammer_ino_rb_compare);
  53
  54 /*
  55  * Inodes are sorted and assigned to slave threads in groups of 128.
  56  * We want a flush group size large enough such that the slave threads
  57  * are not likely to interfere with each other when accessing the B-Tree,
  58  * but not so large that we lose concurrency.
  59  */
  60 #define HAMMER_FLUSH_GROUP_SIZE 128
  61
  62 /*
  63  * Support structures for the flusher threads.
  64  */
  65 struct hammer_flusher_info {
  66         TAILQ_ENTRY(hammer_flusher_info) entry;
  67         struct hammer_mount *hmp;
  68         thread_t        td;
  69         int             runstate;
  70         int             count;
  71         hammer_flush_group_t flg;
  72         hammer_inode_t  work_array[HAMMER_FLUSH_GROUP_SIZE];
  73 };
  74
  75 typedef struct hammer_flusher_info *hammer_flusher_info_t;
  76
  77 /*
  78  * Sync all inodes pending on the flusher.
  79  *
  80  * All flush groups will be flushed.  This does not queue dirty inodes
  81  * to the flush groups, it just flushes out what has already been queued!
  82  */
  83 void
  84 hammer_flusher_sync(hammer_mount_t hmp)
  85 {
  86         int seq;
  87
  88         seq = hammer_flusher_async(hmp, NULL);
  89         hammer_flusher_wait(hmp, seq);
  90 }
  91
  92 /*
  93  * Sync all inodes pending on the flusher - return immediately.
  94  *
  95  * All flush groups will be flushed.
  96  */
  97 int
  98 hammer_flusher_async(hammer_mount_t hmp, hammer_flush_group_t close_flg)
  99 {
 100         hammer_flush_group_t flg;
 101         int seq = hmp->flusher.next;
 102
 103         TAILQ_FOREACH(flg, &hmp->flush_group_list, flush_entry) {
 104                 if (flg->running == 0)
 105                         ++seq;
 106                 flg->closed = 1;
 107                 if (flg == close_flg)
 108                         break;
 109         }
 110         if (hmp->flusher.td) {
 111                 if (hmp->flusher.signal++ == 0)
 112                         wakeup(&hmp->flusher.signal);
 113         } else {
 114                 seq = hmp->flusher.done;
 115         }
 116         return(seq);
 117 }
 118
 119 int
 120 hammer_flusher_async_one(hammer_mount_t hmp)
 121 {
 122         int seq;
 123
 124         if (hmp->flusher.td) {
 125                 seq = hmp->flusher.next;
 126                 if (hmp->flusher.signal++ == 0)
 127                         wakeup(&hmp->flusher.signal);
 128         } else {
 129                 seq = hmp->flusher.done;
 130         }
 131         return(seq);
 132 }
 133
 134 /*
 135  * Wait for the flusher to get to the specified sequence number.
 136  * Signal the flusher as often as necessary to keep it going.
 137  */
 138 void
 139 hammer_flusher_wait(hammer_mount_t hmp, int seq)
 140 {
 141         while ((int)(seq - hmp->flusher.done) > 0) {
 142                 if (hmp->flusher.act != seq) {
 143                         if (hmp->flusher.signal++ == 0)
 144                                 wakeup(&hmp->flusher.signal);
 145                 }
 146                 tsleep(&hmp->flusher.done, 0, "hmrfls", 0);
 147         }
 148 }
 149
 150 void
 151 hammer_flusher_wait_next(hammer_mount_t hmp)
 152 {
 153         int seq;
 154
 155         seq = hammer_flusher_async_one(hmp);
 156         hammer_flusher_wait(hmp, seq);
 157 }
 158
 159 void
 160 hammer_flusher_create(hammer_mount_t hmp)
 161 {
 162         hammer_flusher_info_t info;
 163         int i;
 164
 165         hmp->flusher.signal = 0;
 166         hmp->flusher.act = 0;
 167         hmp->flusher.done = 0;
 168         hmp->flusher.next = 1;
 169         hammer_ref(&hmp->flusher.finalize_lock);
 170         TAILQ_INIT(&hmp->flusher.run_list);
 171         TAILQ_INIT(&hmp->flusher.ready_list);
 172
 173         lwkt_create(hammer_flusher_master_thread, hmp,
 174                     &hmp->flusher.td, NULL, 0, -1, "hammer-M");
 175         for (i = 0; i < HAMMER_MAX_FLUSHERS; ++i) {
 176                 info = kmalloc(sizeof(*info), hmp->m_misc, M_WAITOK|M_ZERO);
 177                 info->hmp = hmp;
 178                 TAILQ_INSERT_TAIL(&hmp->flusher.ready_list, info, entry);
 179                 lwkt_create(hammer_flusher_slave_thread, info,
 180                             &info->td, NULL, 0, -1, "hammer-S%d", i);
 181         }
 182 }
 183
 184 void
 185 hammer_flusher_destroy(hammer_mount_t hmp)
 186 {
 187         hammer_flusher_info_t info;
 188
 189         /*
 190          * Kill the master
 191          */
 192         hmp->flusher.exiting = 1;
 193         while (hmp->flusher.td) {
 194                 ++hmp->flusher.signal;
 195                 wakeup(&hmp->flusher.signal);
 196                 tsleep(&hmp->flusher.exiting, 0, "hmrwex", hz);
 197         }
 198
 199         /*
 200          * Kill the slaves
 201          */
 202         while ((info = TAILQ_FIRST(&hmp->flusher.ready_list)) != NULL) {
 203                 KKASSERT(info->runstate == 0);
 204                 TAILQ_REMOVE(&hmp->flusher.ready_list, info, entry);
 205                 info->runstate = -1;
 206                 wakeup(&info->runstate);
 207                 while (info->td)
 208                         tsleep(&info->td, 0, "hmrwwc", 0);
 209                 kfree(info, hmp->m_misc);
 210         }
 211 }
 212
 213 /*
 214  * The master flusher thread manages the flusher sequence id and
 215  * synchronization with the slave work threads.
 216  */
 217 static void
 218 hammer_flusher_master_thread(void *arg)
 219 {
 220         hammer_flush_group_t flg;
 221         hammer_mount_t hmp;
 222
 223         hmp = arg;
 224
 225         for (;;) {
 226                 /*
 227                  * Do at least one flush cycle.  We may have to update the
 228                  * UNDO FIFO even if no inodes are queued.
 229                  */
 230                 for (;;) {
 231                         while (hmp->flusher.group_lock)
 232                                 tsleep(&hmp->flusher.group_lock, 0, "hmrhld", 0);
 233                         hmp->flusher.act = hmp->flusher.next;
 234                         ++hmp->flusher.next;
 235                         hammer_flusher_clean_loose_ios(hmp);
 236                         hammer_flusher_flush(hmp);
 237                         hmp->flusher.done = hmp->flusher.act;
 238                         wakeup(&hmp->flusher.done);
 239                         flg = TAILQ_FIRST(&hmp->flush_group_list);
 240                         if (flg == NULL || flg->closed == 0)
 241                                 break;
 242                         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 243                                 break;
 244                 }
 245
 246                 /*
 247                  * Wait for activity.
 248                  */
 249                 if (hmp->flusher.exiting && TAILQ_EMPTY(&hmp->flush_group_list))
 250                         break;
 251                 while (hmp->flusher.signal == 0)
 252                         tsleep(&hmp->flusher.signal, 0, "hmrwwa", 0);
 253
 254                 /*
 255                  * Flush for each count on signal but only allow one extra
 256                  * flush request to build up.
 257                  */
 258                 if (--hmp->flusher.signal != 0)
 259                         hmp->flusher.signal = 1;
 260         }
 261
 262         /*
 263          * And we are done.
 264          */
 265         hmp->flusher.td = NULL;
 266         wakeup(&hmp->flusher.exiting);
 267         lwkt_exit();
 268 }
 269
 270 /*
 271  * Flush all inodes in the current flush group.
 272  */
 273 static void
 274 hammer_flusher_flush(hammer_mount_t hmp)
 275 {
 276         hammer_flusher_info_t info;
 277         hammer_flush_group_t flg;
 278         hammer_reserve_t resv;
 279         hammer_inode_t ip;
 280         hammer_inode_t next_ip;
 281         int slave_index;
 282         int count;
 283
 284         /*
 285          * Just in-case there's a flush race on mount
 286          */
 287         if (TAILQ_FIRST(&hmp->flusher.ready_list) == NULL)
 288                 return;
 289
 290         /*
 291          * We only do one flg but we may have to loop/retry.
 292          */
 293         count = 0;
 294         while ((flg = TAILQ_FIRST(&hmp->flush_group_list)) != NULL) {
 295                 ++count;
 296                 if (hammer_debug_general & 0x0001) {
 297                         kprintf("hammer_flush %d ttl=%d recs=%d\n",
 298                                 hmp->flusher.act,
 299                                 flg->total_count, flg->refs);
 300                 }
 301                 if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 302                         break;
 303                 hammer_start_transaction_fls(&hmp->flusher.trans, hmp);
 304
 305                 /*
 306                  * If the previous flush cycle just about exhausted our
 307                  * UNDO space we may have to do a dummy cycle to move the
 308                  * first_offset up before actually digging into a new cycle,
 309                  * or the new cycle will not have sufficient undo space.
 310                  */
 311                 if (hammer_flusher_undo_exhausted(&hmp->flusher.trans, 3))
 312                         hammer_flusher_finalize(&hmp->flusher.trans, 0);
 313
 314                 /*
 315                  * Ok, we are running this flush group now (this prevents new
 316                  * additions to it).
 317                  */
 318                 flg->running = 1;
 319                 if (hmp->next_flush_group == flg)
 320                         hmp->next_flush_group = TAILQ_NEXT(flg, flush_entry);
 321
 322                 /*
 323                  * Iterate the inodes in the flg's flush_tree and assign
 324                  * them to slaves.
 325                  */
 326                 slave_index = 0;
 327                 info = TAILQ_FIRST(&hmp->flusher.ready_list);
 328                 next_ip = RB_FIRST(hammer_fls_rb_tree, &flg->flush_tree);
 329
 330                 while ((ip = next_ip) != NULL) {
 331                         next_ip = RB_NEXT(hammer_fls_rb_tree,
 332                                           &flg->flush_tree, ip);
 333
 334                         if (++hmp->check_yield > hammer_yield_check) {
 335                                 hmp->check_yield = 0;
 336                                 lwkt_user_yield();
 337                         }
 338
 339                         /*
 340                          * Add ip to the slave's work array.  The slave is
 341                          * not currently running.
 342                          */
 343                         info->work_array[info->count++] = ip;
 344                         if (info->count != HAMMER_FLUSH_GROUP_SIZE)
 345                                 continue;
 346
 347                         /*
 348                          * Get the slave running
 349                          */
 350                         TAILQ_REMOVE(&hmp->flusher.ready_list, info, entry);
 351                         TAILQ_INSERT_TAIL(&hmp->flusher.run_list, info, entry);
 352                         info->flg = flg;
 353                         info->runstate = 1;
 354                         wakeup(&info->runstate);
 355
 356                         /*
 357                          * Get a new slave.  We may have to wait for one to
 358                          * finish running.
 359                          */
 360                         while ((info = TAILQ_FIRST(&hmp->flusher.ready_list)) == NULL) {
 361                                 tsleep(&hmp->flusher.ready_list, 0, "hmrfcc", 0);
 362                         }
 363                 }
 364
 365                 /*
 366                  * Run the current slave if necessary
 367                  */
 368                 if (info->count) {
 369                         TAILQ_REMOVE(&hmp->flusher.ready_list, info, entry);
 370                         TAILQ_INSERT_TAIL(&hmp->flusher.run_list, info, entry);
 371                         info->flg = flg;
 372                         info->runstate = 1;
 373                         wakeup(&info->runstate);
 374                 }
 375
 376                 /*
 377                  * Wait for all slaves to finish running
 378                  */
 379                 while (TAILQ_FIRST(&hmp->flusher.run_list) != NULL)
 380                         tsleep(&hmp->flusher.ready_list, 0, "hmrfcc", 0);
 381
 382                 /*
 383                  * Do the final finalization, clean up
 384                  */
 385                 hammer_flusher_finalize(&hmp->flusher.trans, 1);
 386                 hmp->flusher.tid = hmp->flusher.trans.tid;
 387
 388                 hammer_done_transaction(&hmp->flusher.trans);
 389
 390                 /*
 391                  * Loop up on the same flg.  If the flg is done clean it up
 392                  * and break out.  We only flush one flg.
 393                  */
 394                 if (RB_EMPTY(&flg->flush_tree)) {
 395                         KKASSERT(flg->refs == 0);
 396                         TAILQ_REMOVE(&hmp->flush_group_list, flg, flush_entry);
 397                         kfree(flg, hmp->m_misc);
 398                         break;
 399                 }
 400         }
 401
 402         /*
 403          * We may have pure meta-data to flush, or we may have to finish
 404          * cycling the UNDO FIFO, even if there were no flush groups.
 405          */
 406         if (count == 0 && hammer_flusher_haswork(hmp)) {
 407                 hammer_start_transaction_fls(&hmp->flusher.trans, hmp);
 408                 hammer_flusher_finalize(&hmp->flusher.trans, 1);
 409                 hammer_done_transaction(&hmp->flusher.trans);
 410         }
 411
 412         /*
 413          * Clean up any freed big-blocks (typically zone-2).
 414          * resv->flush_group is typically set several flush groups ahead
 415          * of the free to ensure that the freed block is not reused until
 416          * it can no longer be reused.
 417          */
 418         while ((resv = TAILQ_FIRST(&hmp->delay_list)) != NULL) {
 419                 if (resv->flush_group != hmp->flusher.act)
 420                         break;
 421                 hammer_reserve_clrdelay(hmp, resv);
 422         }
 423 }
 424
 425
 426 /*
 427  * The slave flusher thread pulls work off the master flush list until no
 428  * work is left.
 429  */
 430 static void
 431 hammer_flusher_slave_thread(void *arg)
 432 {
 433         hammer_flush_group_t flg;
 434         hammer_flusher_info_t info;
 435         hammer_mount_t hmp;
 436         hammer_inode_t ip;
 437         int i;
 438
 439         info = arg;
 440         hmp = info->hmp;
 441
 442         for (;;) {
 443                 while (info->runstate == 0)
 444                         tsleep(&info->runstate, 0, "hmrssw", 0);
 445                 if (info->runstate < 0)
 446                         break;
 447                 flg = info->flg;
 448
 449                 for (i = 0; i < info->count; ++i) {
 450                         ip = info->work_array[i];
 451                         hammer_flusher_flush_inode(ip, &hmp->flusher.trans);
 452                         ++hammer_stats_inode_flushes;
 453                 }
 454                 info->count = 0;
 455                 info->runstate = 0;
 456                 TAILQ_REMOVE(&hmp->flusher.run_list, info, entry);
 457                 TAILQ_INSERT_TAIL(&hmp->flusher.ready_list, info, entry);
 458                 wakeup(&hmp->flusher.ready_list);
 459         }
 460         info->td = NULL;
 461         wakeup(&info->td);
 462         lwkt_exit();
 463 }
 464
 465 void
 466 hammer_flusher_clean_loose_ios(hammer_mount_t hmp)
 467 {
 468         hammer_buffer_t buffer;
 469         hammer_io_t io;
 470
 471         /*
 472          * loose ends - buffers without bp's aren't tracked by the kernel
 473          * and can build up, so clean them out.  This can occur when an
 474          * IO completes on a buffer with no references left.
 475          */
 476         if ((io = TAILQ_FIRST(&hmp->lose_list)) != NULL) {
 477                 crit_enter();   /* biodone() race */
 478                 while ((io = TAILQ_FIRST(&hmp->lose_list)) != NULL) {
 479                         KKASSERT(io->mod_list == &hmp->lose_list);
 480                         TAILQ_REMOVE(&hmp->lose_list, io, mod_entry);
 481                         io->mod_list = NULL;
 482                         if (io->lock.refs == 0)
 483                                 ++hammer_count_refedbufs;
 484                         hammer_ref(&io->lock);
 485                         buffer = (void *)io;
 486                         hammer_rel_buffer(buffer, 0);
 487                 }
 488                 crit_exit();
 489         }
 490 }
 491
 492 /*
 493  * Flush a single inode that is part of a flush group.
 494  *
 495  * Flusher errors are extremely serious, even ENOSPC shouldn't occur because
 496  * the front-end should have reserved sufficient space on the media.  Any
 497  * error other then EWOULDBLOCK will force the mount to be read-only.
 498  */
 499 static
 500 void
 501 hammer_flusher_flush_inode(hammer_inode_t ip, hammer_transaction_t trans)
 502 {
 503         hammer_mount_t hmp = ip->hmp;
 504         int error;
 505
 506         hammer_flusher_clean_loose_ios(hmp);
 507         error = hammer_sync_inode(trans, ip);
 508
 509         /*
 510          * EWOULDBLOCK can happen under normal operation, all other errors
 511          * are considered extremely serious.  We must set WOULDBLOCK
 512          * mechanics to deal with the mess left over from the abort of the
 513          * previous flush.
 514          */
 515         if (error) {
 516                 ip->flags |= HAMMER_INODE_WOULDBLOCK;
 517                 if (error == EWOULDBLOCK)
 518                         error = 0;
 519         }
 520         hammer_flush_inode_done(ip, error);
 521         while (hmp->flusher.finalize_want)
 522                 tsleep(&hmp->flusher.finalize_want, 0, "hmrsxx", 0);
 523         if (hammer_flusher_undo_exhausted(trans, 1)) {
 524                 kprintf("HAMMER: Warning: UNDO area too small!\n");
 525                 hammer_flusher_finalize(trans, 1);
 526         } else if (hammer_flusher_meta_limit(trans->hmp)) {
 527                 hammer_flusher_finalize(trans, 0);
 528         }
 529 }
 530
 531 /*
 532  * Return non-zero if the UNDO area has less then (QUARTER / 4) of its
 533  * space left.
 534  *
 535  * 1/4 - Emergency free undo space level.  Below this point the flusher
 536  *       will finalize even if directory dependancies have not been resolved.
 537  *
 538  * 2/4 - Used by the pruning and reblocking code.  These functions may be
 539  *       running in parallel with a flush and cannot be allowed to drop
 540  *       available undo space to emergency levels.
 541  *
 542  * 3/4 - Used at the beginning of a flush to force-sync the volume header
 543  *       to give the flush plenty of runway to work in.
 544  */
 545 int
 546 hammer_flusher_undo_exhausted(hammer_transaction_t trans, int quarter)
 547 {
 548         if (hammer_undo_space(trans) <
 549             hammer_undo_max(trans->hmp) * quarter / 4) {
 550                 return(1);
 551         } else {
 552                 return(0);
 553         }
 554 }
 555
 556 /*
 557  * Flush all pending UNDOs, wait for write completion, update the volume
 558  * header with the new UNDO end position, and flush it.  Then
 559  * asynchronously flush the meta-data.
 560  *
 561  * If this is the last finalization in a flush group we also synchronize
 562  * our cached blockmap and set hmp->flusher_undo_start and our cached undo
 563  * fifo first_offset so the next flush resets the FIFO pointers.
 564  *
 565  * If this is not final it is being called because too many dirty meta-data
 566  * buffers have built up and must be flushed with UNDO synchronization to
 567  * avoid a buffer cache deadlock.
 568  */
 569 void
 570 hammer_flusher_finalize(hammer_transaction_t trans, int final)
 571 {
 572         hammer_volume_t root_volume;
 573         hammer_blockmap_t cundomap, dundomap;
 574         hammer_mount_t hmp;
 575         hammer_io_t io;
 576         int count;
 577         int i;
 578
 579         hmp = trans->hmp;
 580         root_volume = trans->rootvol;
 581
 582         /*
 583          * Exclusively lock the flusher.  This guarantees that all dirty
 584          * buffers will be idled (have a mod-count of 0).
 585          */
 586         ++hmp->flusher.finalize_want;
 587         hammer_lock_ex(&hmp->flusher.finalize_lock);
 588
 589         /*
 590          * If this isn't the final sync several threads may have hit the
 591          * meta-limit at the same time and raced.  Only sync if we really
 592          * have to, after acquiring the lock.
 593          */
 594         if (final == 0 && !hammer_flusher_meta_limit(hmp))
 595                 goto done;
 596
 597         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 598                 goto done;
 599
 600         /*
 601          * Flush data buffers.  This can occur asynchronously and at any
 602          * time.  We must interlock against the frontend direct-data write
 603          * but do not have to acquire the sync-lock yet.
 604          */
 605         count = 0;
 606         while ((io = TAILQ_FIRST(&hmp->data_list)) != NULL) {
 607                 if (io->ioerror)
 608                         break;
 609                 if (io->lock.refs == 0)
 610                         ++hammer_count_refedbufs;
 611                 hammer_ref(&io->lock);
 612                 hammer_io_write_interlock(io);
 613                 KKASSERT(io->type != HAMMER_STRUCTURE_VOLUME);
 614                 hammer_io_flush(io, 0);
 615                 hammer_io_done_interlock(io);
 616                 hammer_rel_buffer((hammer_buffer_t)io, 0);
 617                 ++count;
 618         }
 619
 620         /*
 621          * The sync-lock is required for the remaining sequence.  This lock
 622          * prevents meta-data from being modified.
 623          */
 624         hammer_sync_lock_ex(trans);
 625
 626         /*
 627          * If we have been asked to finalize the volume header sync the
 628          * cached blockmap to the on-disk blockmap.  Generate an UNDO
 629          * record for the update.
 630          */
 631         if (final) {
 632                 cundomap = &hmp->blockmap[0];
 633                 dundomap = &root_volume->ondisk->vol0_blockmap[0];
 634                 if (root_volume->io.modified) {
 635                         hammer_modify_volume(trans, root_volume,
 636                                              dundomap, sizeof(hmp->blockmap));
 637                         for (i = 0; i < HAMMER_MAX_ZONES; ++i)
 638                                 hammer_crc_set_blockmap(&cundomap[i]);
 639                         bcopy(cundomap, dundomap, sizeof(hmp->blockmap));
 640                         hammer_modify_volume_done(root_volume);
 641                 }
 642         }
 643
 644         /*
 645          * Flush UNDOs
 646          */
 647         count = 0;
 648         while ((io = TAILQ_FIRST(&hmp->undo_list)) != NULL) {
 649                 if (io->ioerror)
 650                         break;
 651                 KKASSERT(io->modify_refs == 0);
 652                 if (io->lock.refs == 0)
 653                         ++hammer_count_refedbufs;
 654                 hammer_ref(&io->lock);
 655                 KKASSERT(io->type != HAMMER_STRUCTURE_VOLUME);
 656                 hammer_io_flush(io, hammer_undo_reclaim(io));
 657                 hammer_rel_buffer((hammer_buffer_t)io, 0);
 658                 ++count;
 659         }
 660
 661         /*
 662          * Wait for I/Os to complete and flush the cache on the target disk.
 663          */
 664         hammer_flusher_clean_loose_ios(hmp);
 665         hammer_io_wait_all(hmp, "hmrfl1");
 666
 667         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 668                 goto failed;
 669
 670         /*
 671          * HAMMER VERSION < 4:
 672          *      Update the on-disk volume header with new UNDO FIFO end
 673          *      position (do not generate new UNDO records for this change).
 674          *      We have to do this for the UNDO FIFO whether (final) is
 675          *      set or not in order for the UNDOs to be recognized on
 676          *      recovery.
 677          *
 678          * HAMMER VERSION >= 4:
 679          *      The UNDO FIFO data written above will be recognized on
 680          *      recovery without us having to sync the volume header.
 681          *
 682          * Also update the on-disk next_tid field.  This does not require
 683          * an UNDO.  However, because our TID is generated before we get
 684          * the sync lock another sync may have beat us to the punch.
 685          *
 686          * This also has the side effect of updating first_offset based on
 687          * a prior finalization when the first finalization of the next flush
 688          * cycle occurs, removing any undo info from the prior finalization
 689          * from consideration.
 690          *
 691          * The volume header will be flushed out synchronously.
 692          */
 693         dundomap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
 694         cundomap = &hmp->blockmap[HAMMER_ZONE_UNDO_INDEX];
 695
 696         if (dundomap->first_offset != cundomap->first_offset ||
 697                    dundomap->next_offset != cundomap->next_offset) {
 698                 hammer_modify_volume(NULL, root_volume, NULL, 0);
 699                 dundomap->first_offset = cundomap->first_offset;
 700                 dundomap->next_offset = cundomap->next_offset;
 701                 hammer_crc_set_blockmap(dundomap);
 702                 hammer_modify_volume_done(root_volume);
 703         }
 704
 705         /*
 706          * vol0_next_tid is used for TID selection and is updated without
 707          * an UNDO so we do not reuse a TID that may have been rolled-back.
 708          *
 709          * vol0_last_tid is the highest fully-synchronized TID.  It is
 710          * set-up when the UNDO fifo is fully synced, later on (not here).
 711          */
 712         if (root_volume->io.modified) {
 713                 hammer_modify_volume(NULL, root_volume, NULL, 0);
 714                 if (root_volume->ondisk->vol0_next_tid < trans->tid)
 715                         root_volume->ondisk->vol0_next_tid = trans->tid;
 716                 hammer_crc_set_volume(root_volume->ondisk);
 717                 hammer_modify_volume_done(root_volume);
 718                 hammer_io_flush(&root_volume->io, 0);
 719         }
 720
 721         /*
 722          * Wait for I/Os to complete.
 723          *
 724          * For HAMMER VERSION 4+ filesystems we do not have to wait for
 725          * the I/O to complete as the new UNDO FIFO entries are recognized
 726          * even without the volume header update.  This allows the volume
 727          * header to flushed along with meta-data, significantly reducing
 728          * flush overheads.
 729          */
 730         hammer_flusher_clean_loose_ios(hmp);
 731         if (hmp->version < HAMMER_VOL_VERSION_FOUR)
 732                 hammer_io_wait_all(hmp, "hmrfl2");
 733
 734         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 735                 goto failed;
 736
 737         /*
 738          * Flush meta-data.  The meta-data will be undone if we crash
 739          * so we can safely flush it asynchronously.  There is no need
 740          * to wait for I/O to complete (or issue a synchronous disk flush).
 741          *
 742          * In fact, even if we did wait the meta-data will still be undone
 743          * by a crash up until the next flush cycle due to the first_offset
 744          * in the volume header for the UNDO FIFO not being adjusted until
 745          * the following flush cycle.
 746          */
 747         count = 0;
 748         while ((io = TAILQ_FIRST(&hmp->meta_list)) != NULL) {
 749                 if (io->ioerror)
 750                         break;
 751                 KKASSERT(io->modify_refs == 0);
 752                 if (io->lock.refs == 0)
 753                         ++hammer_count_refedbufs;
 754                 hammer_ref(&io->lock);
 755                 KKASSERT(io->type != HAMMER_STRUCTURE_VOLUME);
 756                 hammer_io_flush(io, 0);
 757                 hammer_rel_buffer((hammer_buffer_t)io, 0);
 758                 ++count;
 759         }
 760
 761         /*
 762          * If this is the final finalization for the flush group set
 763          * up for the next sequence by setting a new first_offset in
 764          * our cached blockmap and clearing the undo history.
 765          *
 766          * Even though we have updated our cached first_offset, the on-disk
 767          * first_offset still governs available-undo-space calculations.
 768          */
 769         if (final) {
 770                 cundomap = &hmp->blockmap[HAMMER_ZONE_UNDO_INDEX];
 771                 if (cundomap->first_offset == cundomap->next_offset) {
 772                         hmp->hflags &= ~HMNT_UNDO_DIRTY;
 773                 } else {
 774                         cundomap->first_offset = cundomap->next_offset;
 775                         hmp->hflags |= HMNT_UNDO_DIRTY;
 776                 }
 777                 hammer_clear_undo_history(hmp);
 778
 779                 /*
 780                  * Flush tid sequencing.  flush_tid1 is fully synchronized,
 781                  * meaning a crash will not roll it back.  flush_tid2 has
 782                  * been written out asynchronously and a crash will roll
 783                  * it back.  flush_tid1 is used for all mirroring masters.
 784                  */
 785                 if (hmp->flush_tid1 != hmp->flush_tid2) {
 786                         hmp->flush_tid1 = hmp->flush_tid2;
 787                         wakeup(&hmp->flush_tid1);
 788                 }
 789                 hmp->flush_tid2 = trans->tid;
 790         }
 791
 792         /*
 793          * Cleanup.  Report any critical errors.
 794          */
 795 failed:
 796         hammer_sync_unlock(trans);
 797
 798         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR) {
 799                 kprintf("HAMMER(%s): Critical write error during flush, "
 800                         "refusing to sync UNDO FIFO\n",
 801                         root_volume->ondisk->vol_name);
 802         }
 803
 804 done:
 805         hammer_unlock(&hmp->flusher.finalize_lock);
 806
 807         if (--hmp->flusher.finalize_want == 0)
 808                 wakeup(&hmp->flusher.finalize_want);
 809         hammer_stats_commits += final;
 810 }
 811
 812 /*
 813  * Return non-zero if too many dirty meta-data buffers have built up.
 814  *
 815  * Since we cannot allow such buffers to flush until we have dealt with
 816  * the UNDOs, we risk deadlocking the kernel's buffer cache.
 817  */
 818 int
 819 hammer_flusher_meta_limit(hammer_mount_t hmp)
 820 {
 821         if (hmp->locked_dirty_space + hmp->io_running_space >
 822             hammer_limit_dirtybufspace) {
 823                 return(1);
 824         }
 825         return(0);
 826 }
 827
 828 /*
 829  * Return non-zero if too many dirty meta-data buffers have built up.
 830  *
 831  * This version is used by background operations (mirror, prune, reblock)
 832  * to leave room for foreground operations.
 833  */
 834 int
 835 hammer_flusher_meta_halflimit(hammer_mount_t hmp)
 836 {
 837         if (hmp->locked_dirty_space + hmp->io_running_space >
 838             hammer_limit_dirtybufspace / 2) {
 839                 return(1);
 840         }
 841         return(0);
 842 }
 843
 844 /*
 845  * Return non-zero if the flusher still has something to flush.
 846  */
 847 int
 848 hammer_flusher_haswork(hammer_mount_t hmp)
 849 {
 850         if (hmp->flags & HAMMER_MOUNT_CRITICAL_ERROR)
 851                 return(0);
 852         if (TAILQ_FIRST(&hmp->flush_group_list) ||      /* dirty inodes */
 853             TAILQ_FIRST(&hmp->volu_list) ||             /* dirty buffers */
 854             TAILQ_FIRST(&hmp->undo_list) ||
 855             TAILQ_FIRST(&hmp->data_list) ||
 856             TAILQ_FIRST(&hmp->meta_list) ||
 857             (hmp->hflags & HMNT_UNDO_DIRTY)             /* UNDO FIFO sync */
 858         ) {
 859                 return(1);
 860         }
 861         return(0);
 862 }
 863