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The algorithm for counting freeable objects in the lu_cache shrinker does not scale with the number of cpus. The LU_SS_LRU_LEN counter for each cpu is read and summed at shrink time while holding the lu_sites_guard mutex. With a large number of cpus and low memory conditions, processes bottleneck on the mutex. This mod reduces the time spent counting by using the kernel's percpu counter functions to maintain the length of a site's lru. The summing occurs when a percpu value is incremented or decremented and a threshold is exceeded. lu_cache_shrink_count() simply returns the last such computed sum. This mod also replaces the lu_sites_guard mutex with a rw semaphore. The lock protects the lu_site list, which is modified when a file system is mounted/umounted or when the lu_site is purged. lu_cache_shrink_count simply reads data so it does not need to wait for other readers. lu_cache_shrink_scan, which actually frees the unused objects, is still serialized. Signed-off-by: Ann Koehler <amk@cray.com> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7997 Reviewed-on: http://review.whamcloud.com/19390 Reviewed-by: Andreas Dilger <andreas.dilger@intel.com> Reviewed-by: Bobi Jam <bobijam@hotmail.com> Reviewed-by: Oleg Drokin <oleg.drokin@intel.com> Signed-off-by: James Simmons <jsimmons@infradead.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.