linux-kernel - Re: [PATCH 1/3] writeback: Creating /sys/kernel/mm/writeback/writeback

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Message-ID: <20100619104439.GA7659@lst.de>
Date:	Sat, 19 Jun 2010 12:44:39 +0200
From:	Christoph Hellwig <hch@....de>
To:	Michael Rubin <mrubin@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, jack@...e.cz, akpm@...ux-foundation.org,
	david@...morbit.com, hch@....de, axboe@...nel.dk
Subject: Re: [PATCH 1/3] writeback: Creating /sys/kernel/mm/writeback/writeback

On Fri, Jun 18, 2010 at 05:30:13PM -0700, Michael Rubin wrote:
> Adding the /sys/kernel/mm/writeback/writeback file.  It contains data
> to help developers and applications gain visibility into writeback
> behaviour.
> 
>     # cat /sys/kernel/mm/writeback/writeback
>     pages_dirtied:    3747
>     pages_cleaned:    3618
>     dirty_threshold:  816673
>     bg_threshold:     408336

I'm fine with exposting this. but the interface is rather awkward.
These kinds of multiple value per file interface require addition
parsing and are a pain to extend.  Please do something like

/proc/sys/vm/writeback/

			pages_dirtied
			pages_cleaned
			dirty_threshold
			background_threshold

where you can just read the value from the file.

> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> index c920164..84b0181 100644
> --- a/fs/nilfs2/segment.c
> +++ b/fs/nilfs2/segment.c
> @@ -1598,8 +1598,10 @@ nilfs_copy_replace_page_buffers(struct page *page, struct list_head *out)
>  	} while (bh = bh->b_this_page, bh2 = bh2->b_this_page, bh != head);
>  	kunmap_atomic(kaddr, KM_USER0);
>  
> -	if (!TestSetPageWriteback(clone_page))
> +	if (!TestSetPageWriteback(clone_page)) {
>  		inc_zone_page_state(clone_page, NR_WRITEBACK);
> +		inc_zone_page_state(clone_page, NR_PAGES_ENTERED_WRITEBACK);
> +	}
>  	unlock_page(clone_page);

I'm not very happy about having this opencoded in a filesystem.

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