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Date: Mon, 29 Apr 2013 20:48:17 -0400
From: Rik van Riel <riel@redhat.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: "Pierre-Loup A. Griffais" <pgriffais@valvesoftware.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        sonnyrao@chromium.org,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: IO regression after ab8fabd46f on x86 kernels with high memory
References: <517B1153.8000401@valvesoftware.com> <517B2FB4.30605@redhat.com> <20130427024248.GA1229@cmpxchg.org> <517EEBD1.503@valvesoftware.com> <CA+55aFxcq44JsrrR5KKuT=DZQHCfOE3KHQrcD215T+deYesW2g@mail.gmail.com>
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On 04/29/2013 06:03 PM, Linus Torvalds wrote:

> Seriously, you can compile yourself a 64-bit kernel and continue to
> use your 32-bit user-land. And you can complain to whatever distro you
> used that it didn't do that in the first place. But we're not going to
> bother with trying to tune PAE for some particular load. It's just not
> worth it to anybody.

I can think of one way to "tune PAE" that will help
avoid the breakage, and at the same time draw the
attention of users.

Limit the memory that a 32 bit PAE kernel uses, to
something small enough where the user will not
encounter random breakage.  Maybe 8 or 12GB?

It could also print out a friendly message, to
inform the user they should upgrade to a 64 bit
kernel to enjoy the use of all of their memory.

It is a bit of a heavy stick, but I suspect that
it would clue in all of the affected users.

If you have no objection to this, I'll whip up a
patch.