From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.skyhub.de ([5.9.137.197]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hZIh3-00027c-MT for kexec@lists.infradead.org; Fri, 07 Jun 2019 17:30:23 +0000 Date: Fri, 7 Jun 2019 19:30:16 +0200 From: Borislav Petkov Subject: Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr Message-ID: <20190607173016.GM20269@zn.tnic> References: <1548047768-7656-1-git-send-email-kernelfans@gmail.com> <20190125103924.GB27998@zn.tnic> <20190125134518.GA23595@dhcp-128-65.nay.redhat.com> <20190125140823.GC27998@zn.tnic> <20190128095809.GC3732@dhcp-128-65.nay.redhat.com> <20190128101831.GA27154@zn.tnic> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190128101831.GA27154@zn.tnic> 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: Dave Young , Pingfan Liu Cc: x86@kernel.org, Baoquan He , Randy Dunlap , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Mike Rapoport , Andrew Morton , yinghai@kernel.org, vgoyal@redhat.com On Mon, Jan 28, 2019 at 11:18:31AM +0100, Borislav Petkov wrote: > On Mon, Jan 28, 2019 at 05:58:09PM +0800, Dave Young wrote: > > Another reason is in case ,high we will need automatically reserve a > > region in low area for swiotlb. So for example one use > > crashkernel=256M,high, actual reserved memory is 256M above 4G and > > another 256M under 4G for swiotlb. Normally it is not necessary for > > most people. Thus we can not make ,high as default. > > And how is the poor user to figure out that we decided for her/him that > swiotlb reservation is something not necessary for most people and thus > we fail the crashkernel= reservation? > > IOW, that "logic" above doesn't make a whole lot of sense to me from > user friendliness perspective. So to show what I mean: I'm trying to reserve a crash kernel region on a box here. I tried: crashkernel=64M@16M as it is stated in Documentation/kdump/kdump.txt. Box said: [ 0.000000] crashkernel reservation failed - memory is in use. Oh great. Then I tried: crashkernel=64M@64M Box said: [ 0.000000] crashkernel reservation failed - memory is in use. So I simply did: crashkernel=64M and the box said: [ 0.000000] Reserving 64MB of memory at 3392MB for crashkernel (System RAM: 16271MB) So I could've gone a long time poking at the memory to find a suitable address. So do you see what I mean with making this as user-friendly and as robust as possible? In this case I don't care about *where* my crash kernel is - I only want to have one loaded *somewhere*. And the same strategy should be applied to other reservation attempts - we should try hard to reserve and if we cannot reserve, then try an alternating range. I even think that crashkernel=X@Y should not simply fail if Y is occupied but keep trying and say [ 0.000000] Reserving 64MB of memory at alternative address 3392MB for crashkernel (System RAM: 16271MB) and only fail when the user doesn't really want the kernel to try hard by booting with crashkernel=X@Y,strict But that's for another day. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec