Re: [PATCH v2] jbd2: Avoid long hold times of j_state_lock while committing a transaction

["Theodore Y. Ts'o" <tytso@mit.edu>]

On Thu, Nov 08, 2018 at 01:29:38PM +0100, Jan Kara wrote:
> We can hold j_state_lock for writing at the beginning of
> jbd2_journal_commit_transaction() for a rather long time (reportedly for
> 30 ms) due cleaning revoke bits of all revoked buffers under it. The
> handling of revoke tables as well as cleaning of t_reserved_list, and
> checkpoint lists does not need j_state_lock for anything. It is only
> needed to prevent new handles from joining the transaction. Generally
> T_LOCKED transaction state prevents new handles from joining the
> transaction - except for reserved handles which have to allowed to join
> while we wait for other handles to complete.
> 
> To prevent reserved handles from joining the transaction while cleaning
> up lists, add new transaction state T_SWITCH and watch for it when
> starting reserved handles. With this we can just drop the lock for
> operations that don't need it.
> 
> Reported-and-tested-by: Adrian Hunter <adrian.hunter@intel.com>
> Suggested-by: "Theodore Y. Ts'o" <tytso@mit.edu>
> Signed-off-by: Jan Kara <jack@suse.cz>

Applied, thanks.

						- Ted