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It's a global atomic counter, and we are hitting it at a rate of half a million transactions a second, so it's bouncing the counter cacheline all over the place on large machines. We don't actually need it anymore - it used to be required because the VFS freeze code could not track/prevent filesystem transactions that were running, but that problem no longer exists. Hence to remove the counter, we simply have to ensure that nothing calls xfs_sync_sb() while we are trying to quiesce the filesytem. That only happens if the log worker is still running when we call xfs_quiesce_attr(). The log worker is cancelled at the end of xfs_quiesce_attr() by calling xfs_log_quiesce(), so just call it early here and then we can remove the counter altogether. Concurrent create, 50 million inodes, identical 16p/16GB virtual machines on different physical hosts. Machine A has twice the CPU cores per socket of machine B: unpatched patched machine A: 3m16s 2m00s machine B: 4m04s 4m05s Create rates: unpatched patched machine A: 282k+/-31k 468k+/-21k machine B: 231k+/-8k 233k+/-11k Concurrent rm of same 50 million inodes: unpatched patched machine A: 6m42s 2m33s machine B: 4m47s 4m47s The transaction rate on the fast machine went from just under 300k/sec to 700k/sec, which indicates just how much of a bottleneck this atomic counter was. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
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.