linux-kernel - Re: [PATCH] write-back: fix break condition

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Message-Id: <20090209152140.aa3f50aa.akpm@linux-foundation.org>
Date:	Mon, 9 Feb 2009 15:21:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Federico Cuello <fedux@...men.org.ar>
Cc:	linux-kernel@...r.kernel.org, fedux@...men.org.ar,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] write-back: fix break condition


Thanks, but please do cc the people who were involved with a patch when
you find a problem with it!

On Sat,  7 Feb 2009 01:33:30 -0200
Federico Cuello <fedux@...men.org.ar> wrote:

> Commit 673353723e7a6550625fb719059c5f31cfaecd18 fixed nr_to_write
> counter, but didn't set the break condition properly.

It's actually commit dcf6a79dda5cc2a2bec183e50d829030c0972aaa
("write-back: fix nr_to_write counter").

> If nr_to_write == 0 after being decremented it will loop one more time
> before setting done = 1 and breaking the loop.

We prefer that patches include the author's Signed-off-by:, as per
Documentation/SubmittingPatches, please.

> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index bb5fa2b..9e2ae50 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -981,20 +981,21 @@ continue_unlock:
>  				}
>   			}
>  
> -			if (nr_to_write > 0)
> +			if (nr_to_write > 0) {
>  				nr_to_write--;
> -			else if (wbc->sync_mode == WB_SYNC_NONE) {
> -				/*
> -				 * We stop writing back only if we are not
> -				 * doing integrity sync. In case of integrity
> -				 * sync we have to keep going because someone
> -				 * may be concurrently dirtying pages, and we
> -				 * might have synced a lot of newly appeared
> -				 * dirty pages, but have not synced all of the
> -				 * old dirty pages.
> -				 */
> -				done = 1;
> -				break;
> +				if (nr_to_write == 0 && wbc->sync_mode == WB_SYNC_NONE) {
> +					/*
> +					 * We stop writing back only if we are not
> +					 * doing integrity sync. In case of integrity
> +					 * sync we have to keep going because someone
> +					 * may be concurrently dirtying pages, and we
> +					 * might have synced a lot of newly appeared
> +					 * dirty pages, but have not synced all of the
> +					 * old dirty pages.
> +					 */
> +					done = 1;
> +					break;
> +				}
>  			}
>  
>  			if (wbc->nonblocking && bdi_write_congested(bdi)) {

Artem, Nick, please check?
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