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35c5a09f53
Current work to merge the XFS inode life cycle with the VFS inode
life cycle is finding some interesting issues. If we have a path
that hits buffer trylocks fairly hard (e.g. a non-blocking
background inode freeing function), we end up hitting massive
contention on the buffer cache hash locks:
- 92.71% 0.05% [kernel] [k] xfs_inodegc_worker
- 92.67% xfs_inodegc_worker
- 92.13% xfs_inode_unlink
- 91.52% xfs_inactive_ifree
- 85.63% xfs_read_agi
- 85.61% xfs_trans_read_buf_map
- 85.59% xfs_buf_read_map
- xfs_buf_get_map
- 85.55% xfs_buf_find
- 72.87% _raw_spin_lock
- do_raw_spin_lock
71.86% __pv_queued_spin_lock_slowpath
- 8.74% xfs_buf_rele
- 7.88% _raw_spin_lock
- 7.88% do_raw_spin_lock
7.63% __pv_queued_spin_lock_slowpath
- 1.70% xfs_buf_trylock
- 1.68% down_trylock
- 1.41% _raw_spin_lock_irqsave
- 1.39% do_raw_spin_lock
__pv_queued_spin_lock_slowpath
- 0.76% _raw_spin_unlock
0.75% do_raw_spin_unlock
This is basically hammering the pag->pag_buf_lock from lots of CPUs
doing trylocks at the same time. Most of the buffer trylock
operations ultimately fail after we've done the lookup, so we're
really hammering the buf hash lock whilst making no progress.
We can also see significant spinlock traffic on the same lock just
under normal operation when lots of tasks are accessing metadata
from the same AG, so let's avoid all this by creating a lookup fast
path which leverages the rhashtable's ability to do RCU protected
lookups.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
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Merge tag 'xfs-buf-lockless-lookup-5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs into xfs-5.20-mergeB
xfs: lockless buffer cache lookups
Current work to merge the XFS inode life cycle with the VFS inode
life cycle is finding some interesting issues. If we have a path
that hits buffer trylocks fairly hard (e.g. a non-blocking
background inode freeing function), we end up hitting massive
contention on the buffer cache hash locks:
- 92.71% 0.05% [kernel] [k] xfs_inodegc_worker
- 92.67% xfs_inodegc_worker
- 92.13% xfs_inode_unlink
- 91.52% xfs_inactive_ifree
- 85.63% xfs_read_agi
- 85.61% xfs_trans_read_buf_map
- 85.59% xfs_buf_read_map
- xfs_buf_get_map
- 85.55% xfs_buf_find
- 72.87% _raw_spin_lock
- do_raw_spin_lock
71.86% __pv_queued_spin_lock_slowpath
- 8.74% xfs_buf_rele
- 7.88% _raw_spin_lock
- 7.88% do_raw_spin_lock
7.63% __pv_queued_spin_lock_slowpath
- 1.70% xfs_buf_trylock
- 1.68% down_trylock
- 1.41% _raw_spin_lock_irqsave
- 1.39% do_raw_spin_lock
__pv_queued_spin_lock_slowpath
- 0.76% _raw_spin_unlock
0.75% do_raw_spin_unlock
This is basically hammering the pag->pag_buf_lock from lots of CPUs
doing trylocks at the same time. Most of the buffer trylock
operations ultimately fail after we've done the lookup, so we're
really hammering the buf hash lock whilst making no progress.
We can also see significant spinlock traffic on the same lock just
under normal operation when lots of tasks are accessing metadata
from the same AG, so let's avoid all this by creating a lookup fast
path which leverages the rhashtable's ability to do RCU protected
lookups.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
* tag 'xfs-buf-lockless-lookup-5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs:
xfs: lockless buffer lookup
xfs: remove a superflous hash lookup when inserting new buffers
xfs: reduce the number of atomic when locking a buffer after lookup
xfs: merge xfs_buf_find() and xfs_buf_get_map()
xfs: break up xfs_buf_find() into individual pieces
xfs: rework xfs_buf_incore() API
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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.