From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB776C433F5 for ; Tue, 26 Apr 2022 18:03:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345446AbiDZSGK (ORCPT ); Tue, 26 Apr 2022 14:06:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353052AbiDZSGE (ORCPT ); Tue, 26 Apr 2022 14:06:04 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97FF527CE6; Tue, 26 Apr 2022 11:02:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 3BA90B820F9; Tue, 26 Apr 2022 18:02:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9B48C385A4; Tue, 26 Apr 2022 18:02:49 +0000 (UTC) Date: Tue, 26 Apr 2022 19:02:46 +0100 From: Catalin Marinas To: Zhen Lei Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , linux-kernel@vger.kernel.org, Dave Young , Baoquan He , Vivek Goyal , Eric Biederman , kexec@lists.infradead.org, Will Deacon , linux-arm-kernel@lists.infradead.org, Rob Herring , Frank Rowand , devicetree@vger.kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org, Randy Dunlap , Feng Zhou , Kefeng Wang , Chen Zhou , John Donnelly , Dave Kleikamp Subject: Re: [PATCH v22 5/9] arm64: kdump: Reimplement crashkernel=X Message-ID: References: <20220414115720.1887-1-thunder.leizhen@huawei.com> <20220414115720.1887-6-thunder.leizhen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220414115720.1887-6-thunder.leizhen@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 14, 2022 at 07:57:16PM +0800, Zhen Lei wrote: > /* > * reserve_crashkernel() - reserves memory for crash kernel > * > * This function reserves memory area given in "crashkernel=" kernel command > * line parameter. The memory reserved is used by dump capture kernel when > * primary kernel is crashing. > + * > + * NOTE: Reservation of crashkernel,low is special since its existence > + * is not independent, need rely on the existence of crashkernel,high. > + * Here, four cases of crashkernel low memory reservation are summarized: > + * 1) crashkernel=Y,low is specified explicitly, the size of crashkernel low > + * memory takes Y; > + * 2) crashkernel=,low is not given, while crashkernel=,high is specified, > + * take the default crashkernel low memory size; > + * 3) crashkernel=X is specified, while fallback to get a memory region > + * in high memory, take the default crashkernel low memory size; > + * 4) crashkernel='invalid value',low is specified, failed the whole > + * crashkernel reservation and bail out. Following the x86 behaviour made sense when we were tried to get that code generic. Now that we moved the logic under arch/arm64, we can diverge a bit. I lost track of the original (v1/v2) proposal but I wonder whether we still need the fallback to high for crashkernel=Y. Maybe simpler, no fallbacks: crashkernel=Y - keep the current behaviour, ignore high,low crashkernel=Y,high - allocate above ZONE_DMA crashkernel=Y,low - allocate within ZONE_DMA >From your proposal, the difference is that the Y,high option won't have any default ZONE_DMA fallback, one would have to explicitly pass the Y,low option if needed. Just a thought, maybe it makes the code simpler. But I'm open to discussion if there are good arguments for the proposed (x86-like) behaviour. One argument could be for crashkernel=Y to fall back to high if distros don't want to bother with high/low settings. Another thing I may have asked in the past, what happens if we run a new kernel with these patches with old kexec user tools. I suspect the crashkernel=Y with the fallback to high will confuse the tools. BTW, please separate the NO_BLOCK_MAPPINGS optimisations from the crashkernel above 4G. Let's get the crashkernel reservations sorted first, it's been around for too long. Thanks. -- Catalin