Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752600AbbBXIJd (ORCPT <rfc822;w@1wt.eu>);
	Tue, 24 Feb 2015 03:09:33 -0500
Received: from mail-we0-f177.google.com ([74.125.82.177]:34642 "EHLO
	mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751959AbbBXIJc (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 24 Feb 2015 03:09:32 -0500
Date: Tue, 24 Feb 2015 09:09:27 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Toshi Kani <toshi.kani@hp.com>, hpa@zytor.com, tglx@linutronix.de,
        mingo@redhat.com, arnd@arndb.de, linux-mm@kvack.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, Elliott@hp.com
Subject: Re: [PATCH v2 0/7] Kernel huge I/O mapping support
Message-ID: <20150224080927.GB19069@gmail.com>
References: <1423521935-17454-1-git-send-email-toshi.kani@hp.com>
 <20150223122224.c55554325cc4dadeca067234@linux-foundation.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150223122224.c55554325cc4dadeca067234@linux-foundation.org>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1062
Lines: 32


* Andrew Morton <akpm@linux-foundation.org> wrote:

> <reads the code>
> 
> Oh.  We don't do any checking at all.  We're just telling 
> userspace programmers "don't do that".  hrm.  What are 
> your thoughts on adding the overlap checks to the kernel?

I have requested such sanity checking in previous review as 
well, it has to be made fool-proof for this optimization to 
be usable.

Another alternative would be to make this not a transparent 
optimization, but a separate API: ioremap_hugepage() or so.

The devices and drivers dealing with GBs of remapped pages 
is still relatively low, so they could make explicit use of 
the API and opt in to it.

What I was arguing against was to make it a CONFIG_ option: 
that achieves very little in practice, such APIs should be 
uniformly available.

Thanks,

	Ingo
--
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/