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SubjectRe: [PATCH ] kernel/crash_core.c - Add crashkernel=auto for x86 and Arm
This generally depends on what goes into initrd. Kernel can't know
upfront how big is kdump's initrd going to be. For example, I have
systems with <1TB RAM and 750MB reserved for crashkernel.

Don't think crashkernel=auto can be generalized. RHEL can implement
=auto, because this is a controlled environment (well, in most cases).

On Wed, Dec 4, 2019 at 11:21 AM John Donnelly
<john.p.donnelly@oracle.com> wrote:
>
> This adds crashkernel=auto feature to configure reserved memory for
> vmcore creation to both x86 and Arm platform as implemenented in
> RH 4.18.0-147.el8 kernels. The values have been adjusted for x86 and
> Arm based from 5.4.0 kernel crash testing.
>
> Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
> Tested-by: John Donnelly <john.p.donnelly@oracle.com>
> ---
> Documentation/admin-guide/kdump/kdump.rst | 12 ++++++++++
> kernel/crash_core.c | 28 +++++++++++++++++++++--
> 2 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index ac7e131d2935..7635bbb4ab34 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -285,6 +285,18 @@ 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 if you have enough memory. The threshold
> +is 1G on x86_64, 2G on arm64, ppc64 and ppc64le. The threshold is 4G for s390x.
> +If your system memory is less than the threshold crashkernel=auto will not
> +reserve memory.
> +
> +The automatically reserved memory size varies based on architecture.
> +The size changes according to system memory size like below:
> + x86_64: 1G-64G:160M,64G-1T:280M,1T-:512M
> + s390x: 4G-64G:160M,64G-1T:256M,1T-:512M
> + arm64: 2G-:768M
> + ppc64: 2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G
> +
>
>
> Boot into System Kernel
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 9f1557b98468..564aca60e57f 100644
> --- a/kernel/crash_core.c
> +++ b/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>
> @@ -39,6 +40,15 @@ static int __init parse_crashkernel_mem(char *cmdline,
> unsigned long long *crash_base)
> {
> char *cur = cmdline, *tmp;
> + unsigned long long total_mem = system_ram;
> +
> + /*
> + * Firmware sometimes reserves some memory regions for it's own use.
> + * so we get less than actual system memory size.
> + * Workaround this by round up the total size to 128M which is
> + * enough for most test cases.
> + */
> + total_mem = roundup(total_mem, SZ_128M);
>
> /* for each entry of the comma-separated list */
> do {
> @@ -83,13 +93,13 @@ static int __init parse_crashkernel_mem(char *cmdline,
> return -EINVAL;
> }
> cur = tmp;
> - if (size >= system_ram) {
> + if (size >= total_mem) {
> pr_warn("crashkernel: invalid size\n");
> return -EINVAL;
> }
>
> /* match ? */
> - if (system_ram >= start && system_ram < end) {
> + if (total_mem >= start && total_mem < end) {
> *crash_size = size;
> break;
> }
> @@ -248,6 +258,20 @@ 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) {
> +#ifdef CONFIG_X86_64
> + ck_cmdline = "1G-64G:160M,64G-1T:280M,1T-:512M";
> +#elif defined(CONFIG_S390)
> + ck_cmdline = "4G-64G:160M,64G-1T:256M,1T-:512M";
> +#elif defined(CONFIG_ARM64)
> + ck_cmdline = "2G-:768M";
> +#elif defined(CONFIG_PPC64)
> + ck_cmdline = "2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G";
> +#endif
> + pr_info("Using crashkernel=auto, the size chosen is a best effort estimation.\n");
> + }
> +
> /*
> * if the commandline contains a ':', then that's the extended
> * syntax -- if not, it must be the classic syntax
> --
> 2.20.1
>
>


--
wbr, Vitaly

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