linux-kernel - Re: readahead and oom

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Message-Id: <20110426124743.e58d9746.akpm@linux-foundation.org>
Date:	Tue, 26 Apr 2011 12:47:43 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Dave Young <hidave.darkstar@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mel Gorman <mel@...ux.vnet.ibm.com>
Subject: Re: readahead and oom

On Tue, 26 Apr 2011 17:20:29 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> Pass __GFP_NORETRY|__GFP_NOWARN for readahead page allocations.
> 
> readahead page allocations are completely optional. They are OK to
> fail and in particular shall not trigger OOM on themselves.

I have distinct recollections of trying this many years ago, finding
that it caused problems then deciding not to do it.  But I can't find
an email trail and I don't remember the reasons :(

If the system is so stressed for memory that the oom-killer might get
involved then the readahead pages may well be getting reclaimed before
the application actually gets to use them.  But that's just an aside.

Ho hum.  The patch *seems* good (as it did 5-10 years ago ;)) but there
may be surprising side-effects which could be exposed under heavy
testing.  Testing which I'm sure hasn't been performed...

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