linux-kernel - Re: [PATCH] mm: make VM_MAX

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Date:	Sat, 10 Oct 2009 10:41:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ehrhardt Christian <ehrhardt@...ux.vnet.ibm.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] mm: make VM_MAX_READAHEAD configurable

On Sat, 10 Oct 2009 20:40:42 +0800 Wu Fengguang <fengguang.wu@...el.com> wrote:

> > not sure if it attempts to do anything based on how quickly
> > the device is doing IO. Wu?
> 
> Not for current kernel.  But in fact it's possible to estimate the
> read speed for each individual sequential stream, and possibly drop
> some hint to the IO scheduler: someone will block on this IO after 3
> seconds. But it may not deserve the complexity.

Well, we have a test case.  Would any of your design proposals address
the performance problem which motivated the s390 guys to propose this
patch?

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