Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id <S310470AbSCUXuj>; Thu, 21 Mar 2002 18:50:39 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
	id <S310475AbSCUXu2>; Thu, 21 Mar 2002 18:50:28 -0500
Received: from holomorphy.com ([66.224.33.161]:32142 "EHLO holomorphy")
	by vger.kernel.org with ESMTP id <S310470AbSCUXuO>;
	Thu, 21 Mar 2002 18:50:14 -0500
Date: Thu, 21 Mar 2002 15:49:43 -0800
From: William Lee Irwin III <wli@holomorphy.com>
To: Andrea Arcangeli <andrea@suse.de>
Cc: Christoph Hellwig <hch@suse.de>,
        "Martin J. Bligh" <Martin.Bligh@us.ibm.com>,
        Hugh Dickins <hugh@veritas.com>, Rik van Riel <riel@conectiva.com.br>,
        Dave McCracken <dmccr@us.ibm.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Creating a per-task kernel space for kmap, user pagetables, et al
Message-ID: <20020321234943.GC785@holomorphy.com>
Mail-Followup-To: William Lee Irwin III <wli@holomorphy.com>,
	Andrea Arcangeli <andrea@suse.de>, Christoph Hellwig <hch@suse.de>,
	"Martin J. Bligh" <Martin.Bligh@us.ibm.com>,
	Hugh Dickins <hugh@veritas.com>,
	Rik van Riel <riel@conectiva.com.br>,
	Dave McCracken <dmccr@us.ibm.com>,
	linux-kernel <linux-kernel@vger.kernel.org>
In-Reply-To: <127930000.1016651345@flay> <20020320212341.M4268@dualathlon.random> <20020320203520.A2003@infradead.org> <20020320223425.P4268@dualathlon.random> <20020320214607.A6363@infradead.org> <20020320230002.A16801@dualathlon.random>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Description: brief message
Content-Disposition: inline
User-Agent: Mutt/1.3.25i
Organization: The Domain of Holomorphy
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Mar 20, 2002 at 11:00:02PM +0100, Andrea Arcangeli wrote:
> Thet's another bit yes, but we'll need 200000 tasks to overflow the
> lowmem (ignoring the fact the lowmem is shared also for the other lowmem
> data structures) and there's the PID limit of 64k tasks. So I don't see
> it as a major thing. Anyways if we really wanted to put the stack [and
> task structure of course] in highmem, we could do that in two additional
> entries after the user stack together with the two entries for the
> pagecache and pagetable persistent kmaps. I think we can officially call
> that area the "userfixmap" or "per-process-fixmap" (no matter if it's in
> user or kernel space).  But it is much faster to keep the kernel stack
> always in 4M global tlbs, thus I don't think we need to change that in
> 2.5.  (also USB was used to do dma in the kernel stack, not sure if they
> changed it recently)

Another (perhaps obvious) pitfall is stack-allocated storage used for
components of globally-mapped structures. The premier example of this
is probably waitqueues. To keep them working, dynamic allocation of
globally-mapped storage or per-task static allocation thereof is
required as a substitute.


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