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We've added a new mount options, "checkpoint_merge" and "nocheckpoint_merge", which creates a kernel daemon and makes it to merge concurrent checkpoint requests as much as possible to eliminate redundant checkpoint issues. Plus, we can eliminate the sluggish issue caused by slow checkpoint operation when the checkpoint is done in a process context in a cgroup having low i/o budget and cpu shares. To make this do better, we set the default i/o priority of the kernel daemon to "3", to give one higher priority than other kernel threads. The below verification result explains this. The basic idea has come from https://opensource.samsung.com. [Verification] Android Pixel Device(ARM64, 7GB RAM, 256GB UFS) Create two I/O cgroups (fg w/ weight 100, bg w/ wight 20) Set "strict_guarantees" to "1" in BFQ tunables In "fg" cgroup, - thread A => trigger 1000 checkpoint operations "for i in `seq 1 1000`; do touch test_dir1/file; fsync test_dir1; done" - thread B => gererating async. I/O "fio --rw=write --numjobs=1 --bs=128k --runtime=3600 --time_based=1 --filename=test_img --name=test" In "bg" cgroup, - thread C => trigger repeated checkpoint operations "echo $$ > /dev/blkio/bg/tasks; while true; do touch test_dir2/file; fsync test_dir2; done" We've measured thread A's execution time. [ w/o patch ] Elapsed Time: Avg. 68 seconds [ w/ patch ] Elapsed Time: Avg. 48 seconds Reported-by: kernel test robot <lkp@intel.com> Reported-by: Dan Carpenter <dan.carpenter@oracle.com> [Jaegeuk Kim: fix the return value in f2fs_start_ckpt_thread, reported by Dan] Signed-off-by: Daeho Jeong <daehojeong@google.com> Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
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.