Hi Tiezhu Yang,
On Jan 28, 2022 at 02:20 Tiezhu Yang wrote:
[...]
Hi Petr,
Thank you for your reply.
This is a RFC patch, the initial aim of this patch is to discuss what is
the proper way to support crashkernel=auto.
Well, the point I'm trying to make is that crashkernel=auto cannot be
implemented. Your code would have to know what happens in the future,
and AFAIK time travel has not been discovered yet. ;-)
A better approach is to make a very large allocation initially, e.g.
half of available RAM. The remaining RAM should still be big enough to
start booting the system. Later, when a kdump user-space service knows
what it wants to load, it can shrink the reservation by writing a lower
value into /sys/kernel/kexec_crash_size.
The alternative approach does not need any changes to the kernel, except
maybe adding something like "crashkernel=max".
Just my two cents,
Petr T
A moment ago, I find the following patch, it is more flexible, but it is
not merged into the upstream kernel now.
kernel/crash_core: Add crashkernel=auto for vmcore creation
https://lore.kernel.org/lkml/20210223174153.72802-1-saeed.mirzamohammadi@xxxxxxxxxx/
[...]
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 256cf6d..32c51e2 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -252,6 +252,26 @@ static int __init __parse_crashkernel(char
*cmdline,
if (suffix)
return parse_crashkernel_suffix(ck_cmdline, crash_size,
suffix);
+
+ if (strncmp(ck_cmdline, "auto", 4) == 0) {
+#if defined(CONFIG_X86_64) || defined(CONFIG_S390)
+ ck_cmdline = "1G-4G:160M,4G-64G:192M,64G-1T:256M,1T-:512M";
+#elif defined(CONFIG_ARM64)
+ ck_cmdline = "2G-:448M";
+#elif defined(CONFIG_PPC64)
+ char *fadump_cmdline;
+
+ fadump_cmdline = get_last_crashkernel(cmdline, "fadump=",
NULL);
+ fadump_cmdline = fadump_cmdline ?
+ fadump_cmdline + strlen("fadump=") : NULL;
+ if (!fadump_cmdline || (strncmp(fadump_cmdline, "off", 3) ==
0))
+ ck_cmdline =
"2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G";
+ else
+ ck_cmdline =
"4G-16G:768M,16G-64G:1G,64G-128G:2G,128G-1T:4G,1T-2T:6G,2T-4T:12G,4T-8T:20G,8T-16T:36G,16T-32T:64G,32T-64T:128G,64T-:180G";
+#endif
+ pr_info("Using crashkernel=auto, the size chosen is a best
effort estimation.\n");
+ }
+
How did you even arrive at the above numbers?
Memory requirements for kdump:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_monitoring_and_updating_the_kernel/supported-kdump-configurations-and-targets_managing-monitoring-and-updating-the-kernel#memory-requirements-for-kdump_supported-kdump-configurations-and-targets
I've done some research on
this topic recently (ie. during the last 7 years or so). My x86_64
system with 8G RAM running openSUSE Leap 15.3 seems needs 188M for
saving to the local disk, and 203M to save over the network (using
SFTP). My PPC64 LPAR with 16G RAM running latest Beta of SLES 15 SP4
needs 587M, i.e. with the above numbers it may run out of memory while
saving the dump.
Since this is not the first time, I'm trying to explain things, I've
written a blog post now:
https://sigillatum.tesarici.cz/2022-01-27-whats-wrong-with-crashkernel-auto.html
Thank you, this is useful.
Thanks,
Tiezhu
HTH
Petr Tesarik
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