linux-kernel - Re: [PATCH 03/13] writeback: per-task rate limit on balance_dirty

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Message-ID: <20101117143903.GA11664@localhost>
Date:	Wed, 17 Nov 2010 22:39:03 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/13] writeback: per-task rate limit on
 balance_dirty_pages()

> +	if (pause == 0 && nr_dirty < background_thresh)
> +		current->nr_dirtied_pause = ratelimit_pages(bdi);
> +	else if (pause == 1)
> +		current->nr_dirtied_pause += current->nr_dirtied_pause >> 5;

Sorry here is a bug fix for the above line, it's also pushed to the
git tree.

Thanks,
Fengguang
---
Subject: writeback: fix increasement of nr_dirtied_pause
Date: Wed Nov 17 22:31:26 CST 2010

Fix a bug that

	current->nr_dirtied_pause += current->nr_dirtied_pause >> 5;

does not effectively increase nr_dirtied_pause when it's <= 32.
Thus nr_dirtied_pause may never grow up..

Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
 mm/page-writeback.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-next.orig/mm/page-writeback.c	2010-11-17 22:31:09.000000000 +0800
+++ linux-next/mm/page-writeback.c	2010-11-17 22:31:23.000000000 +0800
@@ -662,7 +662,7 @@ pause:
 	if (pause == 0 && nr_dirty < background_thresh)
 		current->nr_dirtied_pause = ratelimit_pages(bdi);
 	else if (pause == 1)
-		current->nr_dirtied_pause += current->nr_dirtied_pause >> 5;
+		current->nr_dirtied_pause += current->nr_dirtied_pause / 32 + 1;
 	else if (pause >= HZ/10)
 		/*
 		 * when repeated, writing 1 page per 100ms on slow devices,
--
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