linux-kernel - Re: PATCH] fix potential latency issues in JBD's journal code

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Message-ID: <20080706041502.GB21990@mit.edu>
Date:	Sun, 6 Jul 2008 00:15:02 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: PATCH] fix potential latency issues in JBD's journal code

On Fri, Jul 04, 2008 at 07:29:29PM -0700, Arjan van de Ven wrote:
> @@ -165,7 +165,7 @@ static void journal_do_submit_data(struct buffer_head **wbuf, int bufs)
>  	for (i = 0; i < bufs; i++) {
>  		wbuf[i]->b_end_io = end_buffer_write_sync;
>  		/* We use-up our safety reference in submit_bh() */
> -		submit_bh(WRITE, wbuf[i]);
> +		submit_bh(WRITE_SYNC, wbuf[i]);
>  	}
>  }

So I started looking at this patch more closely when trying to
replicate it for ext4.  Don't you want to only use WRITE_SYNC() only
for the very last time in the loop?  Otherwise you end up unplugging
the queue after each bufferhead, which wouldn't be a good thing, right?

    	  	     		       		- Ted
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