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Jeff Mahoney fee7acc361 btrfs: keep trim from interfering with transaction commits 
Commit 499f377f49 (btrfs: iterate over unused chunk space in FITRIM)
fixed free space trimming, but introduced latency when it was running.
This is due to it pinning the transaction using both a incremented
refcount and holding the commit root sem for the duration of a single
trim operation.

This was to ensure safety but it's unnecessary.  We already hold the the
chunk mutex so we know that the chunk we're using can't be allocated
while we're trimming it.

In order to check against chunks allocated already in this transaction,
we need to check the pending chunks list.  To to that safely without
joining the transaction (or attaching than then having to commit it) we
need to ensure that the dev root's commit root doesn't change underneath
us and the pending chunk lists stays around until we're done with it.

We can ensure the former by holding the commit root sem and the latter
by pinning the transaction.  We do this now, but the critical section
covers the trim operation itself and we don't need to do that.

This patch moves the pinning and unpinning logic into helpers and unpins
the transaction after performing the search and check for pending
chunks.

Limiting the critical section of the transaction pinning improves the
latency substantially on slower storage (e.g. image files over NFS).

Fixes: 499f377f49 ("btrfs: iterate over unused chunk space in FITRIM")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2018-10-15 17:23:32 +02:00
arch libnvdimm/dax 4.19-rc8 2018-10-14 08:34:31 +02:00
block blk-wbt: wake up all when we scale up, not down 2018-10-11 13:31:28 -06:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto DMAengine updates for v4.19-rc1 2018-08-18 15:55:59 -07:00
Documentation Char/Misc fixes for 4.19-rc7 2018-10-07 08:15:57 +02:00
drivers Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2018-10-14 08:33:35 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs btrfs: keep trim from interfering with transaction commits 2018-10-15 17:23:32 +02:00
include btrfs: Remove 'objectid' member from struct btrfs_root 2018-10-15 17:23:25 +02:00
init Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2018-10-12 12:35:02 +02:00
lib * Fix a stack overflow in lib/bch.c 2018-10-12 12:54:26 +02:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
mm mm/thp: fix call to mmu_notifier in set_pmd_migration_entry() v2 2018-10-13 09:31:02 +02:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 09:01:59 +02:00
samples samples: disable CONFIG_SAMPLES for UML 2018-10-11 02:15:46 +09:00
scripts Kbuild fixes for v4.19 (2nd) 2018-10-11 19:23:07 +02:00
security Revert "uapi/linux/keyctl.h: don't use C++ reserved keyword as a struct member name" 2018-09-25 13:28:58 +02:00
sound ALSA: hda/realtek - Cannot adjust speaker's volume on Dell XPS 27 7760 2018-10-04 07:50:48 +02:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-12 09:01:59 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Remove obsolete kvm_unmap_hva notifier backend 2018-09-07 15:06:02 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS MAINTAINERS: use the correct location for dt-bindings includes for mux 2018-10-12 17:36:39 +02:00
Makefile Linux 4.19-rc8 2018-10-15 07:20:24 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.