Date: Sat, 10 Oct 2009 10:41:11 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jens Axboe <jens.axboe@oracle.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Ehrhardt Christian <ehrhardt@linux.vnet.ibm.com>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH] mm: make VM_MAX_READAHEAD configurable
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On Sat, 10 Oct 2009 20:40:42 +0800 Wu Fengguang <fengguang.wu@intel.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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