linux-kernel - Re: [PATCH 3/3] readahead: introduce context readahead algorithm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 12 Apr 2009 10:48:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vladislav Bolkhovitin <vst@...b.net>,
	Jens Axboe <jens.axboe@...cle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 3/3] readahead: introduce context readahead algorithm


* Wu Fengguang <fengguang.wu@...el.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@...e.hu>

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