linux-kernel - Re: [PATCH 1/5] Lumpy Reclaim V3

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Message-ID: <Pine.LNX.4.64.0702281008330.21257@schroedinger.engr.sgi.com>
Date:	Wed, 28 Feb 2007 10:14:30 -0800 (PST)
From:	Christoph Lameter <clameter@...r.sgi.com>
To:	Andy Whitcroft <apw@...dowen.org>
cc:	Andrew Morton <akpm@...l.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 1/5] Lumpy Reclaim V3

On Tue, 27 Feb 2007, Andy Whitcroft wrote:

> +static int __isolate_lru_page(struct page *page, int active)
> +{
> +	int ret = -EINVAL;
> +
> +	if (PageLRU(page) && (PageActive(page) == active)) {
> +		ret = -EBUSY;
> +		if (likely(get_page_unless_zero(page))) {
> +			/*
> +			 * Be careful not to clear PageLRU until after we're
> +			 * sure the page is not being freed elsewhere -- the
> +			 * page release code relies on it.
> +			 */
> +			ClearPageLRU(page);
> +			ret = 0;

Is that really necessary? PageLRU is clear when a page is freed right? 
And clearing PageLRU requires the zone->lru_lock since we have to move it 
off the LRU.

> -			ClearPageLRU(page);
> -			target = dst;
> +		active = PageActive(page);

Why are we saving the active state? Page cannot be moved between LRUs 
while we hold the lru lock anyways.
-
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