Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756838Ab1DAODq (ORCPT ); Fri, 1 Apr 2011 10:03:46 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:33969 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756620Ab1DAODo (ORCPT ); Fri, 1 Apr 2011 10:03:44 -0400 Subject: Re: [PATCH 04/12] mm: alloc_contig_freed_pages() added From: Dave Hansen To: Michal Nazarewicz Cc: Marek Szyprowski , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, linux-mm@kvack.org, Kyungmin Park , Andrew Morton , KAMEZAWA Hiroyuki , Ankita Garg , Daniel Walker , Johan MOSSBERG , Mel Gorman , Pawel Osciak In-Reply-To: References: <1301577368-16095-1-git-send-email-m.szyprowski@samsung.com> <1301577368-16095-5-git-send-email-m.szyprowski@samsung.com> <1301587083.31087.1032.camel@nimitz> <1301606078.31087.1275.camel@nimitz> <1301610411.30870.29.camel@nimitz> Content-Type: text/plain; charset="ISO-8859-1" Date: Fri, 01 Apr 2011 07:03:16 -0700 Message-ID: <1301666596.30870.176.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1846 Lines: 44 On Fri, 2011-04-01 at 00:51 +0200, Michal Nazarewicz wrote: > On Fri, 01 Apr 2011 00:26:51 +0200, Dave Hansen > wrote: > >> Bug in the above place does not mean that we could not allocate > >> memory. It means caller is broken. > > > > Could you explain that a bit? > > > > Is this a case where a device is mapped to a very *specific* range of > > physical memory and no where else? What are the reasons for not marking > > it off limits at boot? I also saw some bits of isolation and migration > > in those patches. Can't the migration fail? > > The function is called from alloc_contig_range() (see patch 05/12) which > makes sure that the PFN is valid. Situation where there is not enough > space is caught earlier in alloc_contig_range(). > > alloc_contig_freed_pages() must be given a valid PFN range such that all > the pages in that range are free (as in are within the region tracked by > page allocator) and of MIGRATETYPE_ISOLATE so that page allocator won't > touch them. OK, so it really is a low-level function only. How about a comment that explicitly says this? "Only called from $FOO with the area already isolated." It probably also deserves an __ prefix. > That's why invalid PFN is a bug in the caller and not an exception that > has to be handled. > > Also, the function is not called during boot time. It is called while > system is already running. What kind of success have you had running this in practice? I'd be worried that some silly task or a sticky dentry would end up in the range that you want to allocate in. -- Dave -- 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/