From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Date: Thu, 25 Feb 2021 14:42:38 +0000 From: Catalin Marinas Subject: Re: [PATCH v14 02/11] x86: kdump: make the lower bound of crash kernel reservation consistent Message-ID: <20210225144237.GA23418@arm.com> References: <20210130071025.65258-1-chenzhou10@huawei.com> <20210130071025.65258-3-chenzhou10@huawei.com> <20210224143547.GB28965@arm.com> <20210225070717.GG3553@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210225070717.GG3553@MiWiFi-R3L-srv> 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: Baoquan He Cc: wangkefeng.wang@huawei.com, linux-doc@vger.kernel.org, Chen Zhou , huawei.libin@huawei.com, guohanjun@huawei.com, will@kernel.org, corbet@lwn.net, mingo@redhat.com, dyoung@redhat.com, John.P.donnelly@oracle.com, arnd@arndb.de, xiexiuqi@huawei.com, horms@verge.net.au, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, robh+dt@kernel.org, james.morse@arm.com, rppt@kernel.org, prabhakar.pkin@gmail.com, nsaenzjulienne@suse.de On Thu, Feb 25, 2021 at 03:08:46PM +0800, Baoquan He wrote: > On 02/24/21 at 02:35pm, Catalin Marinas wrote: > > On Sat, Jan 30, 2021 at 03:10:16PM +0800, Chen Zhou wrote: > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > > index da769845597d..27470479e4a3 100644 > > > --- a/arch/x86/kernel/setup.c > > > +++ b/arch/x86/kernel/setup.c > > > @@ -439,7 +439,8 @@ static int __init reserve_crashkernel_low(void) > > > return 0; > > > } > > > > > > - low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX); > > > + low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, CRASH_ALIGN, > > > + CRASH_ADDR_LOW_MAX); > > > if (!low_base) { > > > pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n", > > > (unsigned long)(low_size >> 20)); > > > > Is there any reason why the lower bound can't be 0 in all low cases > > here? (Sorry if it's been already discussed, I lost track) > > Seems like a good question. > > This reserve_crashkernel_low(), paired with reserve_crashkernel_high(), is > used to reserve memory under 4G so that kdump kernel owns memory for dma > buffer allocation. In that case, kernel usually is loaded in high > memory. In x86_64, kernel loading need be aligned to 16M because of > CONFIG_PHYSICAL_START, please see commit 32105f7fd8faa7b ("x86: find > offset for crashkernel reservation automatically"). But for crashkernel > low memory, there seems to be no reason to ask for 16M alignment, if > it's taken as dma buffer memory. > > So we can make a different alignment for low memory only, e.g 2M. But > 16M alignment consistent with crashkernel,high is also fine to me. The > only affect is smaller alignment can increase the possibility of > crashkernel low reservation. I don't mind the 16M alignment in both low and high base. But is there any reason that the lower bound (third argument) cannot be 0 in both reserve_crashkernel() (the low attempt) and reserve_crashkernel_low() cases? The comment in reserve_crashkernel() only talks about the 4G upper bound but not why we need a 16M lower bound. -- Catalin _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec