From: Eric DeVolder <eric.devolder@oracle.com>
To: Baoquan He <bhe@redhat.com>, David Hildenbrand <david@redhat.com>,
Borislav Petkov <bp@alien8.de>
Cc: Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
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
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support
Date: Thu, 27 Oct 2022 14:28:34 -0500 [thread overview]
Message-ID: <368a61e7-818b-2ee4-8c8b-22218373622d@oracle.com> (raw)
In-Reply-To: <Y1qNBDY99Ypan9Ok@MiWiFi-R3L-srv>
On 10/27/22 08:52, Baoquan He wrote:
> On 10/26/22 at 04:54pm, David Hildenbrand wrote:
>> On 26.10.22 16:48, Baoquan He wrote:
>>> On 10/25/22 at 12:31pm, Borislav Petkov wrote:
>>>> On Thu, Oct 13, 2022 at 10:57:28AM +0800, Baoquan He wrote:
>>>>> The concern to range number mainly is on Virt guest systems.
>>>>
>>>> And why would virt emulate 1K hotpluggable DIMM slots and not emulate a
>>>> real machine?
>>
>> IIRC, ACPI only allows for 256 slots. PPC dlpar might provide more.
>>
>>>
>>> Well, currently, mem hotpug is an important feature on virt system to
>>> dynamically increase/shrink memory on the system. If only emulating real
>>> machine, it won't be different than bare metal system.
>>>
>>> IIRC, the ballon driver or virtio-mem feature can add memory board, e.g
>>> 1G, block size is 128M, 8 blocks added. When shrinking this 1G memory
>>> later, it will take best effort way to hot remove memory. Means if any
>>> memory block is occupied, it will be kept there. Finally we could only
>>> remove every second blocks, 4 blocks altogether. Then the left
>>> un-removed blocks will produce 4 separate memory regions. Like this, a
>>> virt guest could have many memory regions in kernel after memory
>>> being added/removed.
>>>
>>> If I am wrong, Please correct me, David.
>>
>> Yes, virtio-mem (but also PPC dlpar) can result in many individual memory
>> blocks with holes in between after hotunplug. Hotplug OTOH, usually tries to
>> "plug" these holes and reduce the total number of memory blocks. It might be
>> rare that our range will be heavily fragmented after unplug, but it's
>> certainly possible.
>>
>> [...]
>>
>>>
>>> Yes, now assume we have a HPE SGI system and it has memory hotplug
>>> capacity. The system itself has already got memory regions more than
>>> 1024. Then when we hot add extra memory board, we want to include the
>>> newly added memory regions into elfcorehdr so that it will be dumped out
>>> in kdump kernel.
>>>
>>> That's why I earlier suggested 2048 for number of memory regions.
>>
>> The more the better, unless "it hurts". Assuming a single memory block is
>> 128 MiB, that would be 256 GiB.
>>
>> Usually, on big systems, the memory block size is 2 GiB. So 4 TiB.
>
> Thanks a lot for these valuable inputs, David.
>
> Hi Boris, Eric
>
> So what's your suggested value for the Kconfig option?
>
> 1) cpu number, 1024?
> 2) memory regions, 2048?
>
> About below draft, any comment? We can decide a value based on our
> knowledge, can adjust later if any real system has more than the number.
>
> +config CRASH_ELF_CORE_PHDRS_NUM
> + depends on CRASH_DUMP && KEXEC_FILE && (HOTPLUG_CPU || MEMORY_HOTPLUG)
> + int
> + default 3072
> + help
> + For the kexec_file_load path, specify the default number of
> + phdr for the vmcore. E.g the memory regions represented by the
> + 'System RAM' entries in /proc/iomem, the cpu notes of each
> + present cpu stored in /sys/devices/system/cpu/cpuX/crash_notes.
>
> Thanks
> Baoquan
>
I prefer to keep CRASH_MAX_MEMORY_RANGES, as explained in my response to your message on October 26.
eric
next prev parent reply other threads:[~2022-10-27 19:29 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-09 21:05 [PATCH v12 0/7] crash: Kernel handling of CPU and memory hot un/plug Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 1/7] crash: move crash_prepare_elf64_headers Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 2/7] crash: prototype change for crash_prepare_elf64_headers Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 3/7] crash: add generic infrastructure for crash hotplug support Eric DeVolder
2022-10-03 17:51 ` Sourabh Jain
2022-10-07 19:14 ` Eric DeVolder
2022-10-17 6:45 ` Sourabh Jain
2022-10-24 9:10 ` Baoquan He
2022-10-26 7:00 ` Sourabh Jain
2022-10-04 6:38 ` Sourabh Jain
2022-10-07 19:19 ` Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 4/7] kexec: exclude elfcorehdr from the segment digest Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 5/7] kexec: exclude hot remove cpu from elfcorehdr notes Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 6/7] crash: memory and cpu hotplug sysfs attributes Eric DeVolder
2022-09-09 21:05 ` [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support Eric DeVolder
2022-09-12 6:52 ` Borislav Petkov
2022-09-13 19:12 ` Eric DeVolder
2022-09-26 19:19 ` Eric DeVolder
2022-09-28 16:07 ` Borislav Petkov
2022-09-28 16:38 ` Borislav Petkov
2022-09-30 15:36 ` Eric DeVolder
2022-09-30 16:50 ` Borislav Petkov
2022-09-30 17:11 ` Eric DeVolder
2022-09-30 17:40 ` Borislav Petkov
2022-10-08 2:35 ` Baoquan He
2022-10-12 17:46 ` Borislav Petkov
2022-10-12 20:19 ` Eric DeVolder
2022-10-12 20:41 ` Borislav Petkov
2022-10-13 2:57 ` Baoquan He
2022-10-25 10:31 ` Borislav Petkov
2022-10-26 14:48 ` Baoquan He
2022-10-26 14:54 ` David Hildenbrand
2022-10-27 13:52 ` Baoquan He
2022-10-27 19:28 ` Eric DeVolder [this message]
2022-10-29 4:27 ` Baoquan He
2022-10-27 19:24 ` Eric DeVolder
2022-10-28 10:19 ` Borislav Petkov
2022-10-28 15:29 ` Eric DeVolder
2022-10-28 17:06 ` Borislav Petkov
2022-10-28 19:26 ` Eric DeVolder
2022-10-28 20:30 ` Borislav Petkov
2022-10-28 20:34 ` Eric DeVolder
2022-10-28 21:22 ` Eric DeVolder
2022-10-28 22:19 ` Borislav Petkov
2022-10-12 20:42 ` Eric DeVolder
2022-10-12 16:20 ` Eric DeVolder
2022-10-25 10:39 ` Borislav Petkov
2022-10-04 7:03 ` Sourabh Jain
2022-10-07 19:56 ` Eric DeVolder
2022-10-04 9:10 ` Sourabh Jain
2022-10-07 20:00 ` Eric DeVolder
2022-10-12 4:55 ` Sourabh Jain
2022-10-12 16:23 ` Eric DeVolder
2022-09-19 7:06 ` Sourabh Jain
2022-10-07 19:33 ` Eric DeVolder
2022-10-17 6:54 ` Sourabh Jain
2022-09-12 3:47 ` [PATCH v12 0/7] crash: Kernel handling of CPU and memory hot un/plug Baoquan He
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