linux-ext4 - Re: [PATCH] ext3: wait on all pending commits in ext3_sync

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Message-ID: <494ADEB3.8010109@redhat.com>
Date:	Thu, 18 Dec 2008 17:37:23 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jan Kara <jack@...e.cz>
CC:	Arthur Jones <ajones@...erbed.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"sct@...hat.com" <sct@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ext3: wait on all pending commits in ext3_sync_fs

Jan Kara wrote:
>   Hello,
> 
>   I'm sorry I'm replying late but I got time to react to this only now...
> 

<snip>

>> I tried this and it too fixes the problem.  FWIW I agree it
>> looks better...
>   Well, shouldn't we rather fix what journal_start_commit() returns?
> The interface which returns 1 when a transaction is already committing or
> a transaction commit has just been started but 0 when we race with
> somebody staring the commit is fairly unusable. Moreover
> ext3_force_commit() will unnecessarily create new sync transaction and
> commit it if there's no transaction running which is quite expensive
> (even merging empty sync handle is not for free because of sync
> transaction batching). But this is minor problem since we probably
> don't care too much about sync() performance - BTW this is probably a
> cause for bug 12224, isn't it?

Yep, it is!  :)

>   BTW: ocfs2 would need fixing as well if done your way since it's
> sync_fs function has been copied over from ext3.
>   To summarized I'd rather see a patch like below (untested) going in
> and your patch reverted... Opinions? I can cookup a JBD2 version of
> the patch in case we agree to go this way.

Thanks, I'll look that over.

In looking at what we have today, I wonder if we can make things smarter
so that we don't commit empty transactions in any case?

-Eric
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