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Filipe Manana 0a8068a3dd btrfs: make ranged full fsyncs more efficient 
Commit 0c713cbab6 ("Btrfs: fix race between ranged fsync and writeback
of adjacent ranges") fixed a bug where we could end up with file extent
items in a log tree that represent file ranges that overlap due to a race
between the hole detection of a ranged full fsync and writeback for a
different file range.

The problem was solved by forcing any ranged full fsync to become a
non-ranged full fsync - setting the range start to 0 and the end offset to
LLONG_MAX. This was a simple solution because the code that detected and
marked holes was very complex, it used to be done at copy_items() and
implied several searches on the fs/subvolume tree. The drawback of that
solution was that we started to flush delalloc for the entire file and
wait for all the ordered extents to complete for ranged full fsyncs
(including ordered extents covering ranges completely outside the given
range). Fortunatelly ranged full fsyncs are not the most common case
(hopefully for most workloads).

However a later fix for detecting and marking holes was made by commit
0e56315ca1 ("Btrfs: fix missing hole after hole punching and fsync
when using NO_HOLES") and it simplified a lot the detection of holes,
and now copy_items() no longer does it and we do it in a much more simple
way at btrfs_log_holes().

This makes it now possible to simply make the code that detects holes to
operate only on the initial range and no longer need to operate on the
whole file, while also avoiding the need to flush delalloc for the entire
file and wait for ordered extents that cover ranges that don't overlap the
given range.

Another special care is that we must skip file extent items that fall
entirely outside the fsync range when copying inode items from the
fs/subvolume tree into the log tree - this is to avoid races with ordered
extent completion for extents falling outside the fsync range, which could
cause us to end up with file extent items in the log tree that have
overlapping ranges - for example if the fsync range is [1Mb, 2Mb], when
we copy inode items we could copy an extent item for the range [0, 512K],
then release the search path and before moving to the next leaf, an
ordered extent for a range of [256Kb, 512Kb] completes - this would
cause us to copy the new extent item for range [256Kb, 512Kb] into the
log tree after we have copied one for the range [0, 512Kb] - the extents
overlap, resulting in a corruption.

So this change just does these steps:

1) When the NO_HOLES feature is enabled it leaves the initial range
   intact - no longer sets it to [0, LLONG_MAX] when the full sync bit
   is set in the inode. If NO_HOLES is not enabled, always set the range
   to a full, just like before this change, to avoid missing file extent
   items representing holes after replaying the log (for both full and
   fast fsyncs);

2) Make the hole detection code to operate only on the fsync range;

3) Make the code that copies items from the fs/subvolume tree to skip
   copying file extent items that cover a range completely outside the
   range of the fsync.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2020-03-23 17:01:56 +01:00
arch x86/mm: split vmalloc_sync_all() 2020-03-21 18:56:06 -07:00
block block: Fix partition support for host aware zoned block devices 2020-03-12 07:54:39 -06:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2020-02-20 15:15:16 -08:00
Documentation Kbuild fixes for v5.6 (3rd) 2020-03-19 09:57:48 -07:00
drivers Merge branch 'akpm' (patches from Andrew) 2020-03-22 10:46:50 -07:00
fs btrfs: make ranged full fsyncs more efficient 2020-03-23 17:01:56 +01:00
include uuid: Remove no more needed macro 2020-03-23 17:01:47 +01:00
init int128: fix __uint128_t compiler test in Kconfig 2020-03-12 07:43:03 +09:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-21 11:22:15 -08:00
kernel x86/mm: split vmalloc_sync_all() 2020-03-21 18:56:06 -07:00
lib uuid: Provide a GUID generator for raw buffer 2020-03-23 17:01:47 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm x86/mm: split vmalloc_sync_all() 2020-03-21 18:56:06 -07:00
net io_uring-5.6-20200320 2020-03-21 11:54:47 -07:00
samples Kbuild updates for v5.6 (2nd) 2020-02-09 16:05:50 -08:00
scripts Kbuild fixes for v5.6 (3rd) 2020-03-19 09:57:48 -07:00
security Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2020-02-20 15:15:16 -08:00
sound ALSA: hda/realtek - Enable the headset of Acer N50-600 with ALC662 2020-03-17 18:06:19 +01:00
tools tools/power turbostat: update version 2020-03-21 00:48:02 -04:00
usr initramfs: restore default compression behavior 2020-03-17 09:50:37 +09:00
virt KVM/arm fixes for 5.6, take #1 2020-02-28 11:50:06 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2020-03-06 21:50:05 +01:00
.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 selftest/lkdtm: Use local .gitignore 2020-03-02 08:39:39 -07:00
.mailmap A handful of small documentation fixes that wandered in. 2020-02-07 13:03:10 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Hand MIPS over to Thomas 2020-02-24 22:43:18 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-03-12 16:19:19 -07:00
Makefile Linux 5.6-rc7 2020-03-22 18:31:56 -07:00
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.