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Qu Wenruo c080b4144b btrfs: defrag: properly update range->start for autodefrag 
[BUG]
After commit 7b508037d4 ("btrfs: defrag: use defrag_one_cluster() to
implement btrfs_defrag_file()") autodefrag no longer properly re-defrag
the file from previously finished location.

[CAUSE]
The recent refactoring of defrag only focuses on defrag ioctl subpage
support, doesn't take autodefrag into consideration.

There are two problems involved which prevents autodefrag to restart its
scan:

- No range.start update
  Previously when one defrag target is found, range->start will be
  updated to indicate where next search should start from.

  But now btrfs_defrag_file() doesn't update it anymore, making all
  autodefrag to rescan from file offset 0.

  This would also make autodefrag to mark the same range dirty again and
  again, causing extra IO.

- No proper quick exit for defrag_one_cluster()
  Currently if we reached or exceed @max_sectors limit, we just exit
  defrag_one_cluster(), and let next defrag_one_cluster() call to do a
  quick exit.
  This makes @cur increase, thus no way to properly know which range is
  defragged and which range is skipped.

[FIX]
The fix involves two modifications:

- Update range->start to next cluster start
  This is a little different from the old behavior.
  Previously range->start is updated to the next defrag target.

  But in the end, the behavior should still be pretty much the same,
  as now we skip to next defrag target inside btrfs_defrag_file().

  Thus if auto-defrag determines to re-scan, then we still do the skip,
  just at a different timing.

- Make defrag_one_cluster() to return >0 to indicate a quick exit
  So that btrfs_defrag_file() can also do a quick exit, without
  increasing @cur to the range end, and re-use @cur to update
  @range->start.

- Add comment for btrfs_defrag_file() to mention the range->start update
  Currently only autodefrag utilize this behavior, as defrag ioctl won't
  set @max_to_defrag parameter, thus unless interrupted it will always
  try to defrag the whole range.

Reported-by: Filipe Manana <fdmanana@suse.com>
Fixes: 7b508037d4 ("btrfs: defrag: use defrag_one_cluster() to implement btrfs_defrag_file()")
Link: https://lore.kernel.org/linux-btrfs/0a269612-e43f-da22-c5bc-b34b1b56ebe8@mailbox.org/
CC: stable@vger.kernel.org # 5.16
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2022-01-19 18:25:56 +01:00
arch - Use the proper CONFIG symbol in a preprocessor check. 2022-01-02 09:02:54 -08:00
block block-5.16-2021-12-19 2021-12-19 12:38:53 -08:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Update to zstd-1.4.10 2021-11-13 15:32:30 -08:00
Documentation Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2022-01-02 10:36:09 -08:00
drivers Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2022-01-02 10:36:09 -08:00
fs btrfs: defrag: properly update range->start for autodefrag 2022-01-19 18:25:56 +01:00
include btrfs: pass fs_info to trace_btrfs_transaction_commit 2022-01-03 15:09:47 +01:00
init kbuild: Fix -Wimplicit-fallthrough=5 error for GCC 5.x and 6.x 2021-11-14 18:59:49 -08:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-11-20 10:35:54 -08:00
kernel Merge branch 'akpm' (patches from Andrew) 2021-12-25 12:30:03 -08:00
lib Merge https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2021-12-08 16:06:44 -08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: vmscan: reduce throttling due to a failure to make progress -fix 2021-12-31 13:12:55 -08:00
net net/ncsi: check for error return from call to nla_put_u32 2021-12-29 17:53:24 -08:00
samples ftrace/samples: Add module to test multi direct modify interface 2021-12-09 13:02:44 -05:00
scripts recordmcount.pl: fix typo in s390 mcount regex 2021-12-24 10:20:12 +01:00
security selinux/stable-5.16 PR 20211228 2021-12-28 13:33:06 -08:00
sound sound fixes for 5.16-rc7 2021-12-23 09:55:58 -08:00
tools perf tools fixes for v5.16: 5th batch 2022-01-02 14:09:03 -08:00
usr initramfs: Check timestamp to prevent broken cpio archive 2021-10-24 13:48:40 +09:00
virt KVM: downgrade two BUG_ONs to WARN_ON_ONCE 2021-11-26 06:43:28 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update email address for Guo Ren 2021-12-10 17:10:55 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: mark more list instances as moderated 2021-12-25 12:20:55 -08:00
Makefile Linux 5.16-rc8 2022-01-02 14:23:25 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.