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From:   Vitaly Mayatskih <v.mayatskih@gmail.com>
Date:   Thu, 5 Dec 2019 10:39:50 -0500
Message-ID: <CAGF4SLgoWVwRJaV4PhjzNM0jhg+6bTSEW21o75J74DD4ziOmYA@mail.gmail.com>
Subject: Re: [PATCH ] kernel/crash_core.c - Add crashkernel=auto for x86 and Arm
To:     John Donnelly <john.p.donnelly@oracle.com>
Cc:     linux-kernel@vger.kernel.org
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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