Date: Sun, 12 Apr 2009 10:48:19 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Vladislav Bolkhovitin <vst@vlnb.net>,
       Jens Axboe <jens.axboe@oracle.com>, Jeff Moyer <jmoyer@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 3/3] readahead: introduce context readahead algorithm
Message-ID: <20090412084819.GA25314@elte.hu>
References: <20090412071950.166891982@intel.com> <20090412072052.686760755@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090412072052.686760755@intel.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1161
Lines: 36


* Wu Fengguang <fengguang.wu@intel.com> wrote:

> Introduce page cache context based readahead algorithm.
> This is to better support concurrent read streams in general.

>  /*
> + * Count contiguously cached pages from @offset-1 to @offset-@max,
> + * this count is a conservative estimation of
> + * 	- length of the sequential read sequence, or
> + * 	- thrashing threshold in memory tight systems
> + */
> +static pgoff_t count_history_pages(struct address_space *mapping,
> +				   struct file_ra_state *ra,
> +				   pgoff_t offset, unsigned long max)
> +{
> +	pgoff_t head;
> +
> +	rcu_read_lock();
> +	head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max);
> +	rcu_read_unlock();
> +
> +	return offset - 1 - head;
> +}

Very elegant method! I suspect this will work far better 
than adding various increasingly more complex heuristics.

Emphatically-Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/