linux-ext4 - Re: [PATCH v2] jbd2: Avoid long hold times of j_state

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Date:   Mon, 3 Dec 2018 23:31:17 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org,
        "Hunter, Adrian" <adrian.hunter@...el.com>
Subject: Re: [PATCH v2] jbd2: Avoid long hold times of j_state_lock while
 committing a transaction

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@...el.com>
> Suggested-by: "Theodore Y. Ts'o" <tytso@....edu>
> Signed-off-by: Jan Kara <jack@...e.cz>

Applied, thanks.

						- Ted