aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/filesystems
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2011-03-25 12:57:40 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-25 12:57:41 -0400
commitae005cbed12d0b340b04b59d6f5c56e710b3895d (patch)
treed464865bcc97bea05eab4eba0d10bcad4ec89b93 /Documentation/filesystems
parent3961cdf85b749f6bab50ad31ee97e9277e7a3b70 (diff)
parent0ba0851714beebb800992e5105a79dc3a4c504b0 (diff)
Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (43 commits) ext4: fix a BUG in mb_mark_used during trim. ext4: unused variables cleanup in fs/ext4/extents.c ext4: remove redundant set_buffer_mapped() in ext4_da_get_block_prep() ext4: add more tracepoints and use dev_t in the trace buffer ext4: don't kfree uninitialized s_group_info members ext4: add missing space in printk's in __ext4_grp_locked_error() ext4: add FITRIM to compat_ioctl. ext4: handle errors in ext4_clear_blocks() ext4: unify the ext4_handle_release_buffer() api ext4: handle errors in ext4_rename jbd2: add COW fields to struct jbd2_journal_handle jbd2: add the b_cow_tid field to journal_head struct ext4: Initialize fsync transaction ids in ext4_new_inode() ext4: Use single thread to perform DIO unwritten convertion ext4: optimize ext4_bio_write_page() when no extent conversion is needed ext4: skip orphan cleanup if fs has unknown ROCOMPAT features ext4: use the nblocks arg to ext4_truncate_restart_trans() ext4: fix missing iput of root inode for some mount error paths ext4: make FIEMAP and delayed allocation play well together ext4: suppress verbose debugging information if malloc-debug is off ... Fi up conflicts in fs/ext4/super.c due to workqueue changes
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/ext4.txt207
1 files changed, 206 insertions, 1 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6ab9442d7eeb..6b050464a90d 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -367,12 +367,47 @@ init_itable=n The lazy itable init code will wait n times the
367 minimizes the impact on the systme performance 367 minimizes the impact on the systme performance
368 while file system's inode table is being initialized. 368 while file system's inode table is being initialized.
369 369
370discard Controls whether ext4 should issue discard/TRIM 370discard Controls whether ext4 should issue discard/TRIM
371nodiscard(*) commands to the underlying block device when 371nodiscard(*) commands to the underlying block device when
372 blocks are freed. This is useful for SSD devices 372 blocks are freed. This is useful for SSD devices
373 and sparse/thinly-provisioned LUNs, but it is off 373 and sparse/thinly-provisioned LUNs, but it is off
374 by default until sufficient testing has been done. 374 by default until sufficient testing has been done.
375 375
376nouid32 Disables 32-bit UIDs and GIDs. This is for
377 interoperability with older kernels which only
378 store and expect 16-bit values.
379
380resize Allows to resize filesystem to the end of the last
381 existing block group, further resize has to be done
382 with resize2fs either online, or offline. It can be
383 used only with conjunction with remount.
384
385block_validity This options allows to enables/disables the in-kernel
386noblock_validity facility for tracking filesystem metadata blocks
387 within internal data structures. This allows multi-
388 block allocator and other routines to quickly locate
389 extents which might overlap with filesystem metadata
390 blocks. This option is intended for debugging
391 purposes and since it negatively affects the
392 performance, it is off by default.
393
394dioread_lock Controls whether or not ext4 should use the DIO read
395dioread_nolock locking. If the dioread_nolock option is specified
396 ext4 will allocate uninitialized extent before buffer
397 write and convert the extent to initialized after IO
398 completes. This approach allows ext4 code to avoid
399 using inode mutex, which improves scalability on high
400 speed storages. However this does not work with nobh
401 option and the mount will fail. Nor does it work with
402 data journaling and dioread_nolock option will be
403 ignored with kernel warning. Note that dioread_nolock
404 code path is only used for extent-based files.
405 Because of the restrictions this options comprises
406 it is off by default (e.g. dioread_lock).
407
408i_version Enable 64-bit inode version support. This option is
409 off by default.
410
376Data Mode 411Data Mode
377========= 412=========
378There are 3 different data modes: 413There are 3 different data modes:
@@ -400,6 +435,176 @@ needs to be read from and written to disk at the same time where it
400outperforms all others modes. Currently ext4 does not have delayed 435outperforms all others modes. Currently ext4 does not have delayed
401allocation support if this data journalling mode is selected. 436allocation support if this data journalling mode is selected.
402 437
438/proc entries
439=============
440
441Information about mounted ext4 file systems can be found in
442/proc/fs/ext4. Each mounted filesystem will have a directory in
443/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
444/proc/fs/ext4/dm-0). The files in each per-device directory are shown
445in table below.
446
447Files in /proc/fs/ext4/<devname>
448..............................................................................
449 File Content
450 mb_groups details of multiblock allocator buddy cache of free blocks
451..............................................................................
452
453/sys entries
454============
455
456Information about mounted ext4 file systems can be found in
457/sys/fs/ext4. Each mounted filesystem will have a directory in
458/sys/fs/ext4 based on its device name (i.e., /sys/fs/ext4/hdc or
459/sys/fs/ext4/dm-0). The files in each per-device directory are shown
460in table below.
461
462Files in /sys/fs/ext4/<devname>
463(see also Documentation/ABI/testing/sysfs-fs-ext4)
464..............................................................................
465 File Content
466
467 delayed_allocation_blocks This file is read-only and shows the number of
468 blocks that are dirty in the page cache, but
469 which do not have their location in the
470 filesystem allocated yet.
471
472 inode_goal Tuning parameter which (if non-zero) controls
473 the goal inode used by the inode allocator in
474 preference to all other allocation heuristics.
475 This is intended for debugging use only, and
476 should be 0 on production systems.
477
478 inode_readahead_blks Tuning parameter which controls the maximum
479 number of inode table blocks that ext4's inode
480 table readahead algorithm will pre-read into
481 the buffer cache
482
483 lifetime_write_kbytes This file is read-only and shows the number of
484 kilobytes of data that have been written to this
485 filesystem since it was created.
486
487 max_writeback_mb_bump The maximum number of megabytes the writeback
488 code will try to write out before move on to
489 another inode.
490
491 mb_group_prealloc The multiblock allocator will round up allocation
492 requests to a multiple of this tuning parameter if
493 the stripe size is not set in the ext4 superblock
494
495 mb_max_to_scan The maximum number of extents the multiblock
496 allocator will search to find the best extent
497
498 mb_min_to_scan The minimum number of extents the multiblock
499 allocator will search to find the best extent
500
501 mb_order2_req Tuning parameter which controls the minimum size
502 for requests (as a power of 2) where the buddy
503 cache is used
504
505 mb_stats Controls whether the multiblock allocator should
506 collect statistics, which are shown during the
507 unmount. 1 means to collect statistics, 0 means
508 not to collect statistics
509
510 mb_stream_req Files which have fewer blocks than this tunable
511 parameter will have their blocks allocated out
512 of a block group specific preallocation pool, so
513 that small files are packed closely together.
514 Each large file will have its blocks allocated
515 out of its own unique preallocation pool.
516
517 session_write_kbytes This file is read-only and shows the number of
518 kilobytes of data that have been written to this
519 filesystem since it was mounted.
520..............................................................................
521
522Ioctls
523======
524
525There is some Ext4 specific functionality which can be accessed by applications
526through the system call interfaces. The list of all Ext4 specific ioctls are
527shown in the table below.
528
529Table of Ext4 specific ioctls
530..............................................................................
531 Ioctl Description
532 EXT4_IOC_GETFLAGS Get additional attributes associated with inode.
533 The ioctl argument is an integer bitfield, with
534 bit values described in ext4.h. This ioctl is an
535 alias for FS_IOC_GETFLAGS.
536
537 EXT4_IOC_SETFLAGS Set additional attributes associated with inode.
538 The ioctl argument is an integer bitfield, with
539 bit values described in ext4.h. This ioctl is an
540 alias for FS_IOC_SETFLAGS.
541
542 EXT4_IOC_GETVERSION
543 EXT4_IOC_GETVERSION_OLD
544 Get the inode i_generation number stored for
545 each inode. The i_generation number is normally
546 changed only when new inode is created and it is
547 particularly useful for network filesystems. The
548 '_OLD' version of this ioctl is an alias for
549 FS_IOC_GETVERSION.
550
551 EXT4_IOC_SETVERSION
552 EXT4_IOC_SETVERSION_OLD
553 Set the inode i_generation number stored for
554 each inode. The '_OLD' version of this ioctl
555 is an alias for FS_IOC_SETVERSION.
556
557 EXT4_IOC_GROUP_EXTEND This ioctl has the same purpose as the resize
558 mount option. It allows to resize filesystem
559 to the end of the last existing block group,
560 further resize has to be done with resize2fs,
561 either online, or offline. The argument points
562 to the unsigned logn number representing the
563 filesystem new block count.
564
565 EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one
566 this ioctl is pointing to) to the donor_fd (the
567 one specified in move_extent structure passed
568 as an argument to this ioctl). Then, exchange
569 inode metadata between orig_fd and donor_fd.
570 This is especially useful for online
571 defragmentation, because the allocator has the
572 opportunity to allocate moved blocks better,
573 ideally into one contiguous extent.
574
575 EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or
576 new group descriptor block. The new group
577 descriptor is described by ext4_new_group_input
578 structure, which is passed as an argument to
579 this ioctl. This is especially useful in
580 conjunction with EXT4_IOC_GROUP_EXTEND,
581 which allows online resize of the filesystem
582 to the end of the last existing block group.
583 Those two ioctls combined is used in userspace
584 online resize tool (e.g. resize2fs).
585
586 EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself.
587 It converts (migrates) ext3 indirect block mapped
588 inode to ext4 extent mapped inode by walking
589 through indirect block mapping of the original
590 inode and converting contiguous block ranges
591 into ext4 extents of the temporary inode. Then,
592 inodes are swapped. This ioctl might help, when
593 migrating from ext3 to ext4 filesystem, however
594 suggestion is to create fresh ext4 filesystem
595 and copy data from the backup. Note, that
596 filesystem has to support extents for this ioctl
597 to work.
598
599 EXT4_IOC_ALLOC_DA_BLKS Force all of the delay allocated blocks to be
600 allocated to preserve application-expected ext3
601 behaviour. Note that this will also start
602 triggering a write of the data blocks, but this
603 behaviour may change in the future as it is
604 not necessary and has been done this way only
605 for sake of simplicity.
606..............................................................................
607
403References 608References
404========== 609==========
405 610