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It's expensive to set buffer flags that are already set, because that causes a costly cache line transition. A common case is setting the "verified" flag during ext4 writes. This patch checks for the flag being set first. With the AIM7/creat-clo benchmark testing on a 48G ramdisk based-on ext4 file system, we see 3.3%(15431->15936) improvement of aim7.jobs-per-min on a 2-sockets broadwell platform. What the benchmark does is: it forks 3000 processes, and each process do the following: a) open a new file b) close the file c) delete the file until loop=100*1000 times. The original patch is contributed by Andi Kleen. Signed-off-by: Andi Kleen <ak@linux.intel.com> Tested-by: Kemi Wang <kemi.wang@intel.com> Signed-off-by: Kemi Wang <kemi.wang@intel.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.