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When an ext4 fs is bogged down by a lot of metadata IOs (in the reported case, it was deletion of millions of files, but any massive amount of journal writes would do), after the journal is filled up, tasks which try to access the filesystem and aren't currently performing the journal writes end up waiting in __jbd2_log_wait_for_space() for journal->j_checkpoint_mutex. Because those mutex sleeps aren't marked as iowait, this condition can lead to misleadingly low iowait and /proc/stat:procs_blocked. While iowait propagation is far from strict, this condition can be triggered fairly easily and annotating these sleeps correctly helps initial diagnosis quite a bit. Use the new mutex_lock_io() for journal->j_checkpoint_mutex so that these sleeps are properly marked as iowait. Reported-by: Mingbo Wan <mingbo@fb.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Kara <jack@suse.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@fb.com Link: http://lkml.kernel.org/r/1477673892-28940-5-git-send-email-tj@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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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.