From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id DA9D26B0169 for ; Fri, 19 Aug 2011 10:02:39 -0400 (EDT) Received: from d06nrmr1806.portsmouth.uk.ibm.com (d06nrmr1806.portsmouth.uk.ibm.com [9.149.39.193]) by mtagate3.uk.ibm.com (8.13.1/8.13.1) with ESMTP id p7JE2Zub021062 for ; Fri, 19 Aug 2011 14:02:35 GMT Received: from d06av09.portsmouth.uk.ibm.com (d06av09.portsmouth.uk.ibm.com [9.149.37.250]) by d06nrmr1806.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p7JE2Z9B2498776 for ; Fri, 19 Aug 2011 15:02:35 +0100 Received: from d06av09.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av09.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p7JE2YUW017024 for ; Fri, 19 Aug 2011 08:02:35 -0600 Subject: Re: [patch v3 2/8] kdump: Make kimage_load_crash_segment() weak From: Michael Holzheu Reply-To: holzheu@linux.vnet.ibm.com In-Reply-To: <20110819134836.GB18656@redhat.com> References: <20110812134849.748973593@linux.vnet.ibm.com> <20110812134907.166585439@linux.vnet.ibm.com> <20110818171541.GC15413@redhat.com> <1313760472.3858.26.camel@br98xy6r> <20110819134836.GB18656@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 19 Aug 2011 16:02:34 +0200 Message-ID: <1313762554.3858.37.camel@br98xy6r> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vivek Goyal Cc: ebiederm@xmission.com, mahesh@linux.vnet.ibm.com, hbabu@us.ibm.com, oomichi@mxs.nes.nec.co.jp, horms@verge.net.au, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-mm@kvack.org Hello Vivek, On Fri, 2011-08-19 at 09:48 -0400, Vivek Goyal wrote: [snip] > > > Michael, > > > > > > Thinking more about it. Can't we provide a arch specific version of > > > kmap() and kunmap() so that we create temporary mappings to copy > > > the pages and then these are torn off. > > > > Isn't kmap/kunmap() used for higmem? These functions are called from > > many different functions in the Linux kernel, not only for kdump. I > > would assume that creating and removing mappings with these functions is > > not what a caller would expect and probably would break the Linux kernel > > at many other places, no? > > [CCing linux-mm] > > Yes it is being used for highmem pages. If arch has not defined kmap() > then generic definition is just returning page_address(page), expecting > that page will be mapped. > > I was wondering that what will be broken if arch decides to extend this > to create temporary mappings for pages which are not HIGHMEM but do > not have any mapping. (Like this special case of s390). At least we have significant additional overhead for all the other places where kmap/kunmap is called. > I guess memory management guys can give a better answer here. As a layman, > kmap() seems to be the way to get a kernel mapping for any page frame > and if one is not already there, then arch might create one on the fly, > like we do for HIGHMEM pages. So the question is can be extend this > to also cover pages which are not highmem but do not have any mappings > on s390. > > > > > Perhaps we can finish this discussion after my vacation. I will change > > my patch series that we even do not need this patch... > > So how are you planning to get rid of this patch without modifying kmap(), > kunmap() implementation for s390? I will update my patch series that we do not remove page tables for crashkernel memory. So everything will be as on other architectures. I hope that we can find a good solution after my vacation. Perhaps then I have enough energy again :-) > > So only two common code patches are remaining. I will send the common > > code patches again and will ask Andrew Morton to integrate them in the > > next merge window.The s390 patches will be integrated by Martin. > > I am fine with merge of other 2 common patches. Once you repost the > series, I will ack those. Great! I will resend the patches and contact Andrew Morton. Thanks! Michael -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org