From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1UIJQd-00023k-VQ for kexec@lists.infradead.org; Wed, 20 Mar 2013 13:51:44 +0000 Date: Wed, 20 Mar 2013 09:51:33 -0400 From: Vivek Goyal Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement Message-ID: <20130320135133.GD17274@redhat.com> References: <20130316040003.15064.62308.stgit@localhost6.localdomain6> <20130316040228.15064.28019.stgit@localhost6.localdomain6> <20130319130229.fe83c985678146980ecc6102@linux-foundation.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130319130229.fe83c985678146980ecc6102@linux-foundation.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Andrew Morton Cc: kexec@lists.infradead.org, heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, lisa.mitchell@hp.com, HATAYAMA Daisuke , kumagai-atsushi@mxc.nes.nec.co.jp, ebiederm@xmission.com, zhangyanfei@cn.fujitsu.com, cpw@sgi.com On Tue, Mar 19, 2013 at 01:02:29PM -0700, Andrew Morton wrote: > On Sat, 16 Mar 2013 13:02:29 +0900 HATAYAMA Daisuke wrote: > > > If there's some vmcore object that doesn't satisfy page-size boundary > > requirement, remap_pfn_range() fails to remap it to user-space. > > > > Objects that posisbly don't satisfy the requirement are ELF note > > segments only. The memory chunks corresponding to PT_LOAD entries are > > guaranteed to satisfy page-size boundary requirement by the copy from > > old memory to buffer in 2nd kernel done in later patch. > > > > This patch doesn't copy each note segment into the 2nd kernel since > > they amount to so large in total if there are multiple CPUs. For > > example, current maximum number of CPUs in x86_64 is 5120, where note > > segments exceed 1MB with NT_PRSTATUS only. > > I don't really understand this. Why does the number of or size of > note segments affect their alignment? > > > --- a/fs/proc/vmcore.c > > +++ b/fs/proc/vmcore.c > > @@ -38,6 +38,8 @@ static u64 vmcore_size; > > > > static struct proc_dir_entry *proc_vmcore = NULL; > > > > +static bool support_mmap_vmcore; > > This is quite regrettable. It means that on some kernels/machines, > mmap(vmcore) simply won't work. This means that people might write > code which works for them, but which will fail for others when deployed > on a small number of machines. > > Can we avoid this? Why can't we just copy the notes even if there are > a large number of them? Actually initially he implemented copying notes to second kernel and I suggested to go other way (Tried too hard to save memory in second kernel). I guess it was not a good idea and copying notes keeps it simple. Thanks Vivek _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec