linux-kernel - Re: [PATCH] jfs: clear PAGECACHE_TAG

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Date:	Fri, 28 Dec 2007 12:33:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	shaggy@...tin.ibm.com, jfs-discussion@...ts.sourceforge.net,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] jfs: clear PAGECACHE_TAG_DIRTY for no-write pages


On Fri, 2007-12-28 at 16:03 +0800, Fengguang Wu wrote:
> Andrew,
> 
> This patch fixed the 'pdflush stuck in D state' bug
>         http://bugzilla.kernel.org/show_bug.cgi?id=9291
> and should be pushed to mainline ASAP.
> ---
> 
> When JFS decides to drop a dirty metapage, it simply clears the META_dirty bit
> and leave alone the PG_dirty and PAGECACHE_TAG_DIRTY bits.
> 
> When such no-write page goes to metapage_writepage(), the `relic'
> PAGECACHE_TAG_DIRTY tag should be cleared, to prevent pdflush from
> repeatedly trying to sync them.
> 
> Also, avoid the redirty when a bio submission is planned.
> 
> Tested-by: Markus Rehbach <Markus.Rehbach@....de>
> Signed-off-by: Fengguang Wu <wfg@...l.ustc.edu.cn> 
> ---

> +++ b/fs/jfs/jfs_metapage.c

> @@ -449,9 +450,15 @@ static int metapage_writepage(struct page *page, struct writeback_control *wbc)
>  			goto dump_bio;
>  
>  		submit_bio(WRITE, bio);
> -	}
> -	if (redirty)
> +	} else if (redirty) {
>  		redirty_page_for_writepage(wbc, page);
> +	} else {
> +		write_lock_irq(&mapping->tree_lock);
> +		radix_tree_tag_clear(&mapping->page_tree,
> +				page_index(page),
> +				PAGECACHE_TAG_DIRTY);
> +		write_unlock_irq(&mapping->tree_lock);
> +	}

I'm not liking this open-coded tag_clear, although I currently fail to
come up with a nice solution.

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