e1a6d26483
When syncing the log we acquire the root's log mutex just to update the root's last_log_commit. This is unnecessary because: 1) At this point there can only be one task updating this value, which is the task committing the current log transaction. Any task that enters btrfs_sync_log() has to wait for the previous log transaction to commit and wait for the current log transaction to commit if someone else already started it (in this case it never reaches to the point of updating last_log_commit, as that is done by the committing task); 2) All readers of the root's last_log_commit don't acquire the root's log mutex. This is to avoid blocking the readers, potentially for too long and because getting a stale value of last_log_commit does not cause any functional problem, in the worst case getting a stale value results in logging an inode unnecessarily. Plus it's actually very rare to get a stale value that results in unnecessarily logging the inode. So in order to avoid unnecessary contention on the root's log mutex, which is used for several different purposes, like starting/joining a log transaction and starting writeback of a log transaction, stop acquiring the log mutex for updating the root's last_log_commit. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.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.