Re: [PATCH v3 1/1] kernel/crash_core: Add crashkernel=auto for vmcore creation

[Kairui Song]

On Thu, Feb 18, 2021 at 10:03 AM Baoquan He <bhe@xxxxxxxxxx> wrote:
>
> On 02/11/21 at 10:08am, Saeed Mirzamohammadi wrote:
> > This adds crashkernel=auto feature to configure reserved memory for
> > vmcore creation. CONFIG_CRASH_AUTO_STR is defined to be set for
> > different kernel distributions and different archs based on their
> > needs.
> >
> > Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
> > Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> > Tested-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> > ---
> >  Documentation/admin-guide/kdump/kdump.rst     |  3 ++-
> >  .../admin-guide/kernel-parameters.txt         |  6 +++++
> >  arch/Kconfig                                  | 24 +++++++++++++++++++
> >  kernel/crash_core.c                           |  7 ++++++
> >  4 files changed, 39 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> > index 2da65fef2a1c..e55cdc404c6b 100644
> > --- a/Documentation/admin-guide/kdump/kdump.rst
> > +++ b/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
> >  =======================
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 7d4e523646c3..aa2099465458 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -736,6 +736,12 @@
> >                       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
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index af14a567b493..f87c88ffa2f8 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -14,6 +14,30 @@ menu "General architecture-dependent options"
> >  config CRASH_CORE
> >       bool
> >
> > +if CRASH_CORE
> > +
> > +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
> > +
> > +endif # CRASH_CORE
>
> Wondering if this CRASH_CORE ifdeffery is a little redundent here
> since CRASH_CORE dependency has been added. Except of this, I like this
> patch. As we discussed in private threads, we can try to push it into
> mainline and continue improving later.
>

I believe "if CRASH_CORE" is not needed as it already "depends on
CRASH_CORE", tested with CRASH_CORE=y or 'not set', it just works.

> > +
> >  config KEXEC_CORE
> >       select CRASH_CORE
> >       bool
> > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > index 106e4500fd53..ab0a2b4b1ffa 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>
> > @@ -250,6 +251,12 @@ static int __init __parse_crashkernel(char *cmdline,
> >       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
> >       /*
> >        * if the commandline contains a ':', then that's the extended
> >        * syntax -- if not, it must be the classic syntax
> > --
> > 2.27.0
> >
>
>
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-- 
Best Regards,
Kairui Song