Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759432Ab3FCQs4 (ORCPT ); Mon, 3 Jun 2013 12:48:56 -0400 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:53798 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758785Ab3FCQsy (ORCPT ); Mon, 3 Jun 2013 12:48:54 -0400 Date: Mon, 3 Jun 2013 18:48:47 +0200 From: Michael Holzheu To: Vivek Goyal Cc: Zhang Yanfei , "Eric W. Biederman" , HATAYAMA Daisuke , Jan Willeke , Martin Schwidefsky , Heiko Carstens , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, Andrew Morton Subject: Re: [PATCH 0/2] kdump/mmap: Fix mmap of /proc/vmcore for s390 Message-ID: <20130603184847.4434c7ea@holzheu> In-Reply-To: <20130603155940.GA6714@redhat.com> References: <51A006CF.90105@gmail.com> <87k3mnahkf.fsf@xmission.com> <51A076FE.3060604@gmail.com> <20130525145217.0549138a@holzheu> <20130528135500.GC7088@redhat.com> <20130529135144.7f95c4c0@holzheu> <20130530203847.GB5968@redhat.com> <20130531162127.6d512233@holzheu> <20130531160158.GC13057@redhat.com> <20130603152718.5ba4d05f@holzheu> <20130603155940.GA6714@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13060316-0342-0000-0000-00000535F922 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2522 Lines: 62 On Mon, 3 Jun 2013 11:59:40 -0400 Vivek Goyal wrote: > On Mon, Jun 03, 2013 at 03:27:18PM +0200, Michael Holzheu wrote: > > [..] > > > If not, how would remap_pfn_range() work with HSA region when > > > /proc/vmcore is mmaped()? > > > > I am no memory management expert, so I discussed that with Martin > > Schwidefsky (s390 architecture maintainer). Perhaps something like > > the following could work: > > > > After vmcore_mmap() is called the HSA pages are not initially > > mapped in the page tables. So when user space accesses those parts > > of /proc/vmcore, a fault will be generated. We implement a mechanism > > that in this case the HSA is copied to a new page in the page cache > > and a mapping is created for it. Since the page is allocated in the > > page cache, it can be released afterwards by the kernel when we get > > memory pressure. > > > > Our current idea for such an implementation: > > > > * Create new address space (struct address_space) for /proc/vmcore. > > * Implement new vm_operations_struct "vmcore_mmap_ops" with > > new vmcore_fault() ".fault" callback for /proc/vmcore. > > * Set vma->vm_ops to vmcore_mmap_ops in mmap_vmcore(). > > * The vmcore_fault() function will get a new page cache page, > > copy HSA page to page cache page add it to vmcore address space. > > To see how this could work, we looked into the functions > > filemap_fault() in "mm/filemap.c" and relay_buf_fault() in > > "kernel/relay.c". > > > > What do you think? > > I am not mm expert either but above proposal sounds reasonable to me. > > So remap_pfn_range() call will go in arch dependent code so that arch > can decide which range can be mapped right away and which ranges will > be filed in when fault happens? I am assuming that s390 will map > everything except for pfn between 0 and HSA_SIZE. Yes, for [0 - HSA_SIZE] the fault handler will be called and for the rest we establish a mapping with remap_pfn_range() as it is currently done. Therefore no fault handler will be called for that part of /proc/vmcore. I will try to find out if it is doable that way. > And regular s390 kdump will map everyting right away and will not > have to rely on fault mechanism? Yes, as kdump on the other archs. Thanks Michael -- 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/