From: David Hildenbrand <david@redhat.com>
To: Baoquan He <bhe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
andreyknvl@google.com, christian.brauner@ubuntu.com,
colin.king@canonical.com, corbet@lwn.net, dyoung@redhat.com,
frederic@kernel.org, gpiccoli@canonical.com,
john.p.donnelly@oracle.com, jpoimboe@redhat.com,
keescook@chromium.org, linux-mm@kvack.org, masahiroy@kernel.org,
mchehab+huawei@kernel.org, mike.kravetz@oracle.com,
mingo@kernel.org, mm-commits@vger.kernel.org, paulmck@kernel.org,
peterz@infradead.org, rdunlap@infradead.org, rostedt@goodmis.org,
rppt@kernel.org, saeed.mirzamohammadi@oracle.com,
samitolvanen@google.com, sboyd@kernel.org, tglx@linutronix.de,
torvalds@linux-foundation.org, vgoyal@redhat.com,
yifeifz2@illinois.edu
Subject: Re: [patch 48/91] kernel/crash_core: add crashkernel=auto for vmcore creation
Date: Sat, 8 May 2021 11:22:18 +0200 [thread overview]
Message-ID: <2d0f53d9-51ca-da57-95a3-583dc81f35ef@redhat.com> (raw)
In-Reply-To: <20210508085133.GA2946@localhost.localdomain>
>> Let me take a look .... oh, there it is from 2009
>>
>> https://marc.info/?t=125006512600002&r=1&w=2
>>
>> and then we had it in 2018
>>
>> https://lkml.org/lkml/2018/5/20/262
>
> Thanks for digging these two out, otherwise I may need do for people to
> know the history better.
Sure, I stumbled over this myself recently when wondering about what
fadump is.
>> The issue I have with this: it's just plain wrong when you take memory
>> hotplug into serious account as we see it quite heavily in VMs. You don't
>> know what you'll need when building a kernel. Just pass it via the cmdline
>
> Hmm, kdump may have no issue with memory hotplug in crashkernel
> reservation aspect. The system RAM size is not correlated to
> crashkernel size directly, that's why the default value in this patch is
"Not correlated directly" ...
"1G-64G:128M,64G-1T:256M,1T-:512M"
Am I still asleep and dreaming? :)
> not linear related to system RAM size. The proportion of crashkernel
> size to the total RAM size is thing we take into account. Usually
> crashkernel 160M is enough on most of systems. If system RAM size is
> larger, extra memory can be added just in case, and not bring much
> impact to system.
So, all the rules we have are essentially broken because they rely
completely on the system RAM during boot.
>
> With our investigation, PCIe devices impact the crashkernel size, and
> cpu number. There are always pci devices which driver require tens of KB
> meomry, even MB. E.g in below patch, my colleague Coiby found out the
> i40e network card even cost 1.5G memory to initialize its ringbuffer on
> ppc, and 85M on x86_64.
>
> [PATCH v1 0/3] Reducing memory usage of i40e for kdump
> http://lists.infradead.org/pipermail/kexec/2021-March/022117.html
>
> Even though not all pci devices need surprisingly large memory like
> i40e, system with hundreds of pci devices can also cost more memory than
> expected. This kind of system usually is high end server, specified
> crashkernel value need be set manually.
>
> So system RAM size is the least important part to influence crashkernel
Aehm, not with fadump, no?
> costing. Say my x1 laptop, even though I extended the RAM to 100TB, 160M
> crashkernel is still enough. Just we would like to get a tiny extra part
> to add to crashkernel if the total RAM is very large, that's the rule
> for crashkernel=auto. As for VMs, given their very few devices, virtio
> disk, NAT nic, etc, no matter how much memory is deployed and hot
> added/removed, crashkernel size won't be influenced very much. My
> personal understanding about it.
That's an interesting observation. But you're telling me that we end up
wasting memory for the crashkernel because "crashkernel=auto" which is
supposed to do something magical good automatically does something very
suboptimal? Oh my ... this is broken.
Long story short: crashkernel=auto is pure ugliness.
Why can't we construct a crashkernel in user space when
installing/activating kdump and requiring a reboot for kdump to be
active as long as that crashkernel setting is not properly respected?
Just have a look at the system properties (is_qemu(), #PCI, ...) and
propose a value for "crashkernel=". Check that that value is at least
active when activating kdump. Otherwise don't enable kdump and fail.
Yes, it can be difficult with some newer/older kernels having some
different demands, but things should change drastically, and a distro
can always update its advises along with the kernel, no?
You could even have a kernel interface that gives you the current
crashkernel size (maybe already there) vs. the recommended crashkernel
size. Make kdump or *whoever* activate that in the cmdline and let kdump
check if both values are satisfied when booting up.
Also: this approach here doesn't make any sense when you want to do
something dependent on other cmdline parameters. Take "fadump=on" vs
"fadump=off" as an example. You just cannot handle it properly as
proposed in this patch. To me the approach in this patch makes least
sense TBH.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-05-08 9:22 UTC|newest]
Thread overview: 119+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-07 1:01 incoming Andrew Morton
2021-05-07 1:02 ` [patch 01/91] alpha: eliminate old-style function definitions Andrew Morton
2021-05-07 1:02 ` [patch 02/91] alpha: csum_partial_copy.c: add function prototypes from <net/checksum.h> Andrew Morton
2021-05-07 1:02 ` [patch 03/91] fs/proc/generic.c: fix incorrect pde_is_permanent check Andrew Morton
2021-05-07 1:02 ` [patch 04/91] proc: save LOC in __xlate_proc_name() Andrew Morton
2021-05-07 2:24 ` Linus Torvalds
2021-05-07 1:02 ` [patch 05/91] proc: mandate ->proc_lseek in "struct proc_ops" Andrew Morton
2021-05-07 1:02 ` [patch 06/91] proc: delete redundant subset=pid check Andrew Morton
2021-05-07 1:02 ` [patch 07/91] selftests: proc: test subset=pid Andrew Morton
2021-05-07 1:02 ` [patch 08/91] proc/sysctl: fix function name error in comments Andrew Morton
2021-05-07 1:02 ` [patch 09/91] include: remove pagemap.h from blkdev.h Andrew Morton
2021-05-07 1:02 ` [patch 10/91] kernel.h: drop inclusion in bitmap.h Andrew Morton
2021-05-07 1:02 ` [patch 11/91] linux/profile.h: remove unnecessary declaration Andrew Morton
2021-05-07 1:02 ` [patch 12/91] kernel/async.c: fix pr_debug statement Andrew Morton
2021-05-07 1:02 ` [patch 13/91] kernel/cred.c: make init_groups static Andrew Morton
2021-05-07 1:02 ` [patch 14/91] tools: disable -Wno-type-limits Andrew Morton
2021-05-07 1:02 ` [patch 15/91] tools: bitmap: sync function declarations with the kernel Andrew Morton
2021-05-07 1:02 ` [patch 16/91] tools: sync BITMAP_LAST_WORD_MASK() macro " Andrew Morton
2021-05-07 1:02 ` [patch 17/91] arch: rearrange headers inclusion order in asm/bitops for m68k, sh and h8300 Andrew Morton
2021-05-07 1:02 ` [patch 18/91] lib: extend the scope of small_const_nbits() macro Andrew Morton
2021-05-07 1:03 ` [patch 19/91] tools: sync small_const_nbits() macro with the kernel Andrew Morton
2021-05-07 1:03 ` [patch 20/91] lib: inline _find_next_bit() wrappers Andrew Morton
2021-05-07 1:03 ` [patch 21/91] tools: sync find_next_bit implementation Andrew Morton
2021-05-07 1:03 ` [patch 22/91] lib: add fast path for find_next_*_bit() Andrew Morton
2021-05-07 1:03 ` [patch 23/91] lib: add fast path for find_first_*_bit() and find_last_bit() Andrew Morton
2021-05-07 1:03 ` [patch 24/91] tools: sync lib/find_bit implementation Andrew Morton
2021-05-07 1:03 ` [patch 25/91] MAINTAINERS: add entry for the bitmap API Andrew Morton
2021-05-07 1:03 ` [patch 26/91] lib/bch.c: fix a typo in the file bch.c Andrew Morton
2021-05-07 1:03 ` [patch 27/91] lib: fix inconsistent indenting in process_bit1() Andrew Morton
2021-05-07 1:03 ` [patch 28/91] lib/list_sort.c: fix typo in function description Andrew Morton
2021-05-07 1:03 ` [patch 29/91] lib/genalloc.c: fix a typo Andrew Morton
2021-05-07 1:03 ` [patch 30/91] lib: crc8: pointer to data block should be const Andrew Morton
2021-05-07 1:03 ` [patch 31/91] lib: stackdepot: turn depot_lock spinlock to raw_spinlock Andrew Morton
2021-05-07 1:03 ` [patch 32/91] lib/percpu_counter: tame kernel-doc compile warning Andrew Morton
2021-05-07 1:03 ` [patch 33/91] lib/genalloc: add parameter description to fix doc " Andrew Morton
2021-05-07 1:03 ` [patch 34/91] lib: parser: clean up kernel-doc Andrew Morton
2021-05-07 1:03 ` [patch 35/91] include/linux/compat.h: remove unneeded declaration from COMPAT_SYSCALL_DEFINEx() Andrew Morton
2021-05-07 1:03 ` [patch 36/91] checkpatch: warn when missing newline in return sysfs_emit() formats Andrew Morton
2021-05-07 1:03 ` [patch 37/91] checkpatch: exclude four preprocessor sub-expressions from MACRO_ARG_REUSE Andrew Morton
2021-05-07 1:04 ` [patch 38/91] checkpatch: improve ALLOC_ARRAY_ARGS test Andrew Morton
2021-05-07 1:04 ` [patch 39/91] kselftest: introduce new epoll test case Andrew Morton
2021-05-07 1:04 ` [patch 40/91] fs/epoll: restore waking from ep_done_scan() Andrew Morton
2021-05-07 1:04 ` [patch 41/91] isofs: fix fall-through warnings for Clang Andrew Morton
2021-05-07 1:04 ` [patch 42/91] fs/nilfs2: fix misspellings using codespell tool Andrew Morton
2021-05-07 1:04 ` [patch 43/91] nilfs2: fix typos in comments Andrew Morton
2021-05-07 1:04 ` [patch 44/91] hpfs: replace one-element array with flexible-array member Andrew Morton
2021-05-07 1:04 ` [patch 45/91] do_wait: make PIDTYPE_PID case O(1) instead of O(n) Andrew Morton
2021-05-07 1:04 ` [patch 46/91] kernel/fork.c: simplify copy_mm() Andrew Morton
2021-05-07 1:04 ` [patch 47/91] kernel/fork.c: fix typos Andrew Morton
2021-05-07 1:04 ` [patch 48/91] kernel/crash_core: add crashkernel=auto for vmcore creation Andrew Morton
2021-05-07 7:25 ` Linus Torvalds
2021-05-08 3:13 ` Baoquan He
2021-05-08 3:29 ` Baoquan He
2021-05-07 8:16 ` David Hildenbrand
2021-05-08 8:51 ` Baoquan He
2021-05-08 9:22 ` David Hildenbrand [this message]
2021-05-10 4:53 ` Baoquan He
2021-05-10 8:32 ` David Hildenbrand
2021-05-10 10:43 ` Baoquan He
2021-05-10 11:01 ` David Hildenbrand
2021-05-10 11:44 ` Dave Young
2021-05-10 11:56 ` David Hildenbrand
2021-05-11 13:36 ` Baoquan He
2021-05-11 16:31 ` Mike Rapoport
2021-05-11 17:07 ` David Hildenbrand
2021-05-12 14:51 ` Baoquan He
2021-05-12 15:07 ` David Hildenbrand
2021-05-13 5:04 ` Baoquan He
2021-05-12 19:03 ` Kairui Song
2021-05-17 8:22 ` David Hildenbrand
2021-05-18 8:49 ` Baoquan He
2021-05-18 8:51 ` David Hildenbrand
2021-05-18 9:24 ` Dave Young
2021-05-12 14:13 ` Baoquan He
2021-05-12 7:42 ` Dave Young
2021-05-07 1:04 ` [patch 49/91] kexec: add kexec reboot string Andrew Morton
2021-05-07 1:04 ` [patch 50/91] kernel: kexec_file: fix error return code of kexec_calculate_store_digests() Andrew Morton
2021-05-07 1:04 ` [patch 51/91] kexec: dump kmessage before machine_kexec Andrew Morton
2021-05-07 1:04 ` [patch 52/91] gcov: combine common code Andrew Morton
2021-05-07 1:04 ` [patch 53/91] gcov: simplify buffer allocation Andrew Morton
2021-05-07 1:04 ` [patch 54/91] gcov: use kvmalloc() Andrew Morton
2021-05-07 1:04 ` [patch 55/91] gcov: clang: drop support for clang-10 and older Andrew Morton
2021-05-07 1:04 ` [patch 56/91] smp: kernel/panic.c - silence warnings Andrew Morton
2021-05-07 1:05 ` [patch 57/91] delayacct: clear right task's flag after blkio completes Andrew Morton
2021-05-07 1:05 ` [patch 58/91] gdb: lx-symbols: store the abspath() Andrew Morton
2021-05-07 1:05 ` [patch 59/91] scripts/gdb: document lx_current is only supported by x86 Andrew Morton
2021-05-07 1:05 ` [patch 60/91] scripts/gdb: add lx_current support for arm64 Andrew Morton
2021-05-07 1:05 ` [patch 61/91] kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources Andrew Morton
2021-05-07 1:05 ` [patch 62/91] kernel/resource: make walk_mem_res() find all busy IORESOURCE_MEM resources Andrew Morton
2021-05-07 1:05 ` [patch 63/91] kernel/resource: remove first_lvl / siblings_only logic Andrew Morton
2021-05-07 1:05 ` [patch 64/91] kernel/resource: allow region_intersects users to hold resource_lock Andrew Morton
2021-05-07 1:05 ` [patch 65/91] kernel/resource: refactor __request_region to allow external locking Andrew Morton
2021-05-07 1:05 ` [patch 66/91] kernel/resource: fix locking in request_free_mem_region Andrew Morton
2021-05-07 1:05 ` [patch 67/91] selftests: remove duplicate include Andrew Morton
2021-05-07 1:05 ` [patch 68/91] kernel/async.c: stop guarding pr_debug() statements Andrew Morton
2021-05-07 1:05 ` [patch 69/91] kernel/async.c: remove async_unregister_domain() Andrew Morton
2021-05-07 1:05 ` [patch 70/91] init/initramfs.c: do unpacking asynchronously Andrew Morton
2021-05-07 1:05 ` [patch 71/91] modules: add CONFIG_MODPROBE_PATH Andrew Morton
2021-05-07 1:05 ` [patch 72/91] ipc/sem.c: mundane typo fixes Andrew Morton
2021-05-07 1:05 ` [patch 73/91] mm: fix some typos and code style problems Andrew Morton
2021-05-07 1:05 ` [patch 74/91] drivers/char: remove /dev/kmem for good Andrew Morton
2021-05-07 1:06 ` [patch 75/91] mm: remove xlate_dev_kmem_ptr() Andrew Morton
2021-05-07 1:06 ` [patch 76/91] mm/vmalloc: remove vwrite() Andrew Morton
2021-05-07 1:06 ` [patch 77/91] arm: print alloc free paths for address in registers Andrew Morton
2021-05-07 1:06 ` [patch 78/91] scripts/spelling.txt: add "overlfow" Andrew Morton
2021-05-07 1:06 ` [patch 79/91] scripts/spelling.txt: add "diabled" typo Andrew Morton
2021-05-07 1:06 ` [patch 80/91] scripts/spelling.txt: add "overflw" Andrew Morton
2021-05-07 1:06 ` [patch 81/91] mm/slab.c: fix spelling mistake "disired" -> "desired" Andrew Morton
2021-05-07 1:06 ` [patch 82/91] include/linux/pgtable.h: few spelling fixes Andrew Morton
2021-05-07 1:06 ` [patch 83/91] kernel/umh.c: fix some spelling mistakes Andrew Morton
2021-05-07 1:06 ` [patch 84/91] kernel/user_namespace.c: fix typos Andrew Morton
2021-05-07 1:06 ` [patch 85/91] kernel/up.c: fix typo Andrew Morton
2021-05-07 1:06 ` [patch 86/91] kernel/sys.c: " Andrew Morton
2021-05-07 1:06 ` [patch 87/91] fs: fat: fix spelling typo of values Andrew Morton
2021-05-07 1:06 ` [patch 88/91] ipc/sem.c: spelling fix Andrew Morton
2021-05-07 1:06 ` [patch 89/91] treewide: remove editor modelines and cruft Andrew Morton
2021-05-07 1:06 ` [patch 90/91] mm: fix typos in comments Andrew Morton
2021-05-07 1:06 ` [patch 91/91] " Andrew Morton
2021-05-07 7:12 ` incoming Linus Torvalds
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