From: Jan Kara <jack@suse.cz>
To: Andreas Dilger <adilger@dilger.ca>
Cc: Jan Kara <jack@suse.cz>, Ted Tso <tytso@mit.edu>,
linux-ext4@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 2/2] jbd2: Avoid leaking transaction credits when unreserving handle
Date: Wed, 20 May 2020 15:27:37 +0200 [thread overview]
Message-ID: <20200520132737.GC30597@quack2.suse.cz> (raw)
In-Reply-To: <20AA140E-877B-4240-9BEF-91D24215AF45@dilger.ca>
On Tue 19-05-20 18:44:25, Andreas Dilger wrote:
> On May 18, 2020, at 3:21 AM, Jan Kara <jack@suse.cz> wrote:
> >
> > When reserved transaction handle is unused, we subtract its reserved
> > credits in __jbd2_journal_unreserve_handle() called from
> > jbd2_journal_stop(). However this function forgets to remove reserved
> > credits from transaction->t_outstanding_credits and thus the transaction
> > space that was reserved remains effectively leaked. The leaked
> > transaction space can be quite significant in some cases and leads to
> > unnecessarily small transactions and thus reducing throughput of the
> > journalling machinery. E.g. fsmark workload creating lots of 4k files
> > was observed to have about 20% lower throughput due to this when ext4 is
> > mounted with dioread_nolock mount option.
> >
> > Subtract reserved credits from t_outstanding_credits as well.
> >
> > CC: stable@vger.kernel.org
> > Fixes: 8f7d89f36829 ("jbd2: transaction reservation support")
> > Signed-off-by: Jan Kara <jack@suse.cz>
>
> Patch looks reasonable, with one minor nit below.
>
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Thanks!
> > @@ -721,8 +728,10 @@ static void stop_this_handle(handle_t *handle)
> > }
> > atomic_sub(handle->h_total_credits,
> > &transaction->t_outstanding_credits);
> > - if (handle->h_rsv_handle)
> > - __jbd2_journal_unreserve_handle(handle->h_rsv_handle);
> > + if (handle->h_rsv_handle) {
> > + __jbd2_journal_unreserve_handle(handle->h_rsv_handle,
> > + transaction);
> > + }
>
> There isn't any need for braces {} around this one-line if-block.
Yeah, I'm always undecided about this. I agree that in this case the code
wouldn't be any less readable without the braces. So I'll remove them and
resend with your tag.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-05-20 13:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200518092120.10322-1-jack@suse.cz>
2020-05-18 9:21 ` [PATCH 2/2] jbd2: Avoid leaking transaction credits when unreserving handle Jan Kara
2020-05-20 0:44 ` Andreas Dilger
2020-05-20 13:27 ` Jan Kara [this message]
2020-05-22 0:12 ` Sasha Levin
[not found] <20200520133119.1383-1-jack@suse.cz>
2020-05-20 13:31 ` Jan Kara
2020-05-29 2:44 ` Theodore Y. Ts'o
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