linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Baoquan He <bhe@redhat.com>
To: David Hildenbrand <david@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 16:51:33 +0800	[thread overview]
Message-ID: <20210508085133.GA2946@localhost.localdomain> (raw)
In-Reply-To: <889c6b90-7335-71ce-c955-3596e6ac7c5a@redhat.com>

On 05/07/21 at 10:16am, David Hildenbrand wrote:
> On 07.05.21 03:04, Andrew Morton wrote:
......
> > 
> >   Documentation/admin-guide/kdump/kdump.rst       |    3 +-
> >   Documentation/admin-guide/kernel-parameters.txt |    6 ++++
> >   arch/Kconfig                                    |   20 ++++++++++++++
> >   kernel/crash_core.c                             |    7 ++++
> >   4 files changed, 35 insertions(+), 1 deletion(-)
> > 
> > --- a/arch/Kconfig~kernel-crash_core-add-crashkernel=auto-for-vmcore-creation
> > +++ a/arch/Kconfig
> > @@ -14,6 +14,26 @@ menu "General architecture-dependent opt
> >   config CRASH_CORE
> >   	bool
> > +config CRASH_AUTO_STR
> > +	string "Memory reserved for crash kernel"
> > +	depends on CRASH_CORE
> > +	default "1G-64G:128M,64G-1T:256M,1T-:512M"
> > +	help
> > +	  This configures the reserved memory dependent
> > +	  on the value of System RAM. The syntax is:
> > +	  crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
> > +	              range=start-[end]
> > +
> > +	  For example:
> > +	      crashkernel=512M-2G:64M,2G-:128M
> > +
> > +	  This would mean:
> > +
> > +	      1) if the RAM is smaller than 512M, then don't reserve anything
> > +	         (this is the "rescue" case)
> > +	      2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> > +	      3) if the RAM size is larger than 2G, then reserve 128M
> > +
> >   config KEXEC_CORE
> >   	select CRASH_CORE
> >   	bool
> > --- a/Documentation/admin-guide/kdump/kdump.rst~kernel-crash_core-add-crashkernel=auto-for-vmcore-creation
> > +++ a/Documentation/admin-guide/kdump/kdump.rst
> > @@ -285,7 +285,8 @@ This would mean:
> >       2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> >       3) if the RAM size is larger than 2G, then reserve 128M
> > -
> > +Or you can use crashkernel=auto to choose the crash kernel memory size
> > +based on the recommended configuration set for each arch.
> >   Boot into System Kernel
> >   =======================
> > --- a/Documentation/admin-guide/kernel-parameters.txt~kernel-crash_core-add-crashkernel=auto-for-vmcore-creation
> > +++ a/Documentation/admin-guide/kernel-parameters.txt
> > @@ -751,6 +751,12 @@
> >   			a memory unit (amount[KMG]). See also
> >   			Documentation/admin-guide/kdump/kdump.rst for an example.
> > +	crashkernel=auto
> > +			[KNL] This parameter will set the reserved memory for
> > +			the crash kernel based on the value of the CRASH_AUTO_STR
> > +			that is the best effort estimation for each arch. See also
> > +			arch/Kconfig for further details.
> > +
> >   	crashkernel=size[KMG],high
> >   			[KNL, X86-64] range could be above 4G. Allow kernel
> >   			to allocate physical memory region from top, so could
> > --- a/kernel/crash_core.c~kernel-crash_core-add-crashkernel=auto-for-vmcore-creation
> > +++ a/kernel/crash_core.c
> > @@ -7,6 +7,7 @@
> >   #include <linux/crash_core.h>
> >   #include <linux/utsname.h>
> >   #include <linux/vmalloc.h>
> > +#include <linux/kexec.h>
> >   #include <asm/page.h>
> >   #include <asm/sections.h>
> > @@ -250,6 +251,12 @@ static int __init __parse_crashkernel(ch
> >   	if (suffix)
> >   		return parse_crashkernel_suffix(ck_cmdline, crash_size,
> >   				suffix);
> > +#ifdef CONFIG_CRASH_AUTO_STR
> > +	if (strncmp(ck_cmdline, "auto", 4) == 0) {
> > +		ck_cmdline = CONFIG_CRASH_AUTO_STR;
> > +		pr_info("Using crashkernel=auto, the size chosen is a best effort estimation.\n");
> > +	}
> > +#endif
> I remember that the original "crashkernel=auto" as once proposed by Red Hat
> people did not receive a warm welcome.
> 
> 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.

> 
> 
> 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 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.

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
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.

Thanks
Baoquan



  reply	other threads:[~2021-05-08  8:52 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 [this message]
2021-05-08  9:22       ` David Hildenbrand
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210508085133.GA2946@localhost.localdomain \
    --to=bhe@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=andreyknvl@google.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=colin.king@canonical.com \
    --cc=corbet@lwn.net \
    --cc=david@redhat.com \
    --cc=dyoung@redhat.com \
    --cc=frederic@kernel.org \
    --cc=gpiccoli@canonical.com \
    --cc=john.p.donnelly@oracle.com \
    --cc=jpoimboe@redhat.com \
    --cc=keescook@chromium.org \
    --cc=linux-mm@kvack.org \
    --cc=masahiroy@kernel.org \
    --cc=mchehab+huawei@kernel.org \
    --cc=mike.kravetz@oracle.com \
    --cc=mingo@kernel.org \
    --cc=mm-commits@vger.kernel.org \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rdunlap@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=rppt@kernel.org \
    --cc=saeed.mirzamohammadi@oracle.com \
    --cc=samitolvanen@google.com \
    --cc=sboyd@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --cc=vgoyal@redhat.com \
    --cc=yifeifz2@illinois.edu \
    --subject='Re: [patch 48/91] kernel/crash_core: add crashkernel=auto for vmcore creation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).