From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from terminus.zytor.com ([2001:1868:205::10] helo=mail.zytor.com) by merlin.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1U0gLr-0004O0-Tt for kexec@lists.infradead.org; Wed, 30 Jan 2013 22:41:57 +0000 Message-ID: <5109A1A7.1040609@zytor.com> Date: Wed, 30 Jan 2013 14:41:43 -0800 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH 0/3] Cleanup kdump memmap= passing and e820 usage References: <1358866935-18458-1-git-send-email-trenn@suse.de> <201301301713.43946.trenn@suse.de> <4dc77552-977d-4761-860e-afdec61c4317@email.android.com> <201301301739.52358.trenn@suse.de> <51094FD5.2070909@zytor.com> <87obg6sdtv.fsf@xmission.com> <510992C7.2050000@zytor.com> <877gmumizr.fsf@xmission.com> <51099A3E.5090705@zytor.com> <87ehh2l2z3.fsf@xmission.com> In-Reply-To: <87ehh2l2z3.fsf@xmission.com> 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-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: "Eric W. Biederman" Cc: x86@kernel.org, kexec@lists.infradead.org, Simon Horman , yinghai@kernel.org, Thomas Renninger , vgoyal@redhat.com On 01/30/2013 02:29 PM, Eric W. Biederman wrote: >> >>> I think I would prefer that to call that new type RESERVED_MEM or >>> RESERVED_CACHABLE. Being more specific is fine but dumpable certainly >>> doesn't bring to mind what we are saying. Especially since we already >>> communicate which areas were memory to the last kernel in an >>> architecture generic format. >> >> I was thinking that marking them differently might help debugging, at >> least, but yes, we can have a RESERVED_MEM type. >> >> However, Thomas does have a point that the current use of fairly small >> positive values for Linux-defined types is a bad idea. We should use >> negative types, or at least something north of 0x40000000 or so. > > Yes. It doesn't much matter in the kernel but when it because part of > the ABI it is a real issue. > > Since old kernels treat any value they don't understand as reserved > passing a modified e820 map seems reasonable to me once we have reserved > a special linux value for it. > Just to prevent the possible funnies (including collisions with -errno) that might be caused by negative numbers, I suggest we assign Linux-specific values starting at some huge but still positive value like 2000000000 -- that way we avoid any possible uses of negative errno values internally in the kernel. The bigger question is if we need a separate value from the current E820_RESERVED_KERN. Since it is always easier to have multiple values with the same semantics than it is to have too few, I would still prefer we added a new E820_RESERVED_KDUMP, which would then be 2000000001. What do you think? -hpa _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec