Re: [PATCH] Btrfs: remove unnecessary delalloc mutex for inodes

[David Sterba <dsterba@suse.cz>]

On Fri, Oct 25, 2019 at 10:52:42AM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> The inode delalloc mutex was added a long time ago by commit f248679e86fea
> ("Btrfs: add a delalloc mutex to inodes for delalloc reservations"), and
> the reason for its introduction is not very clear from the change log. It
> claims it solves bogus warnings from lockdep, however it lacks an example
> report/warning from lockdep, or any explanation.
> 
> Since we have enough concurrentcy protection from the locks of the space
> info and block reserve objects, and such lockdep warnings don't seem to
> exist anymore (at least on a 5.3 kernel I couldn't get them with fstests,
> ltp, fs_mark, etc), remove it, simplifying things a bit and decreasing
> the size of the btrfs_inode structure. With some quick fio tests doing
> direct IO and mmap writes I couldn't observe any significant performance
> increase either (direct IO writes that don't increase the file's size
> don't hold the inode's lock for their entire duration and mmap writes
> don't hold the inode's lock at all), which are the only type of writes
> that could see any performance gain due to less serialization.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next with Josef's comment. Thanks.