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Wed, 12 Oct 2022 20:19:27 +0000 Received: from CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::f7b2:af85:fe37:31a7]) by CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::f7b2:af85:fe37:31a7%7]) with mapi id 15.20.5709.021; Wed, 12 Oct 2022 20:19:26 +0000 Message-ID: <53aed03e-2eed-09b1-9532-fe4e497ea47d@oracle.com> Date: Wed, 12 Oct 2022 15:19:19 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.1 Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support Content-Language: en-US To: Borislav Petkov , Baoquan He Cc: Oscar Salvador , Andrew Morton , david@redhat.com, linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, sourabhjain@linux.ibm.com, linux-mm@kvack.org References: <20220909210509.6286-1-eric.devolder@oracle.com> <20220909210509.6286-8-eric.devolder@oracle.com> From: Eric DeVolder In-Reply-To: Content-Type: text/plain; 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Certainly not 32K. > > So you can choose a sane default which covers *all* actual systems out > there. We run here QEMU with the ability for 1024 DIMM slots. A DIMM can be any reasonable power of 2 size, and then that DIMM is further divided into memblocks, typically 128MiB. So, for example, 1TiB requires 1024 DIMMs of 1GiB each with 128MiB memblocks, that results in 8K possible memory regions. So just going to 4TiB reaches 32K memory regions. This I can attest for virtualized DIMMs, not sure about other memory hotplug technologies like virtio-mem or DynamicMemory. But it seems reasonable that those technologies could also easily reach into these number ranges. Eric > >> For the Kconfig CRASH_MAX_MEMORY_RANGES Eric added, it's meaningful to >> me to set a fixed value which is enough in reality. > > Yes, exactly. > >> For extreme testing with special purpose, it could be broken easily, >> people need decide by self whether the CONFIG_CRASH_MAX_MEMORY_RANGES >> is enlarged or not. > > I don't want for people to decide on one more thing where they have to > go and read a bunch of specs just to know what is a good value. So we > should set a sane, *practical* upper limit and simply go with it. > > Everything else is testing stuff and if you test the kernel, then you > can change limits and values and so on as you want to. > > Thx. >