On Mon, 21 May 2018 10:53:37 +0800 Dave Young <dyo...@redhat.com> wrote:
> This is a rework of the crashkernel=auto patches back to 2009 although > I'm not sure if below is the last version of the old effort: > https://lkml.org/lkml/2009/8/12/61 > https://lwn.net/Articles/345344/ > > I changed the original design, instead of adding the auto reserve logic > in code, in this patch just introduce two kernel config options for > the default crashkernel value in MB and the threshold of system memory > in MB so that only reserve default when system memory is equal or > above the threshold. > > With the kernel configs distributions can easily change the default > values so that people do not need to manually set kernel cmdline > for common use cases and one can still overwrite the default value > with manual setup or disable it by using crashkernel=0 > > Signed-off-by: Dave Young <dyo...@redhat.com> > --- > Another difference is with original design the crashkernel size scales > with system memory, according to test, large machine may need more > memory in kdump kernel because of several factors: > 1. cpu numbers, because of the percpu memory allocated for cpus. > (kdump can use nr_cpus=1 to workaround this, but some > arches do not support nr_cpus=X for example powerpc) > 2. IO devices, large system can have a lot of io devices, although we > can try to only add those device drivers we needed, it is still a > problem because of some built-in drivers, some stacked logical devices > eg. device mapper devices, acpi etc. Even if only considering the > meta data for driver model it will still be a big number eg. sysfs > files etc. > 3. The minimum memory requirement for some device drivers are big, even > if some of them have implemented low meory profile. It is usual to see > 10M memory use for a storage driver. > 4. user space initramfs size growing. Busybox is not usable if we need > to add udev support and some complicate storage support. Use dracut > with systemd, especially networking stuff need more memory. > > So probably add another kernel config option to scale the memory size > eg. CRASHKERNEL_DEFAULT_SCALE_RATIO is also good to have, in RHEL we > use base_value + system_mem >> (2^14) for x86. I'm still hesatating > how to describe and add this option. Any suggestions will be appreciated. > > ... > > --- linux-x86.orig/arch/Kconfig > +++ linux-x86/arch/Kconfig > @@ -10,6 +10,22 @@ config KEXEC_CORE > select CRASH_CORE > bool > > +config CRASHKERNEL_DEFAULT_THRESHOLD_MB > + int "System memory size threshold for kdump memory default reserving" > + depends on CRASH_CORE > + default 0 > + help > + CRASHKERNEL_DEFAULT_MB is used as default crashkernel value if > + the system memory size is equal or bigger than the threshold. "the threshold" is rather vague. Can it be clarified? In fact I'm really struggling to understand the logic here.... > +config CRASHKERNEL_DEFAULT_MB > + int "Default crashkernel memory size reserved for kdump" > + depends on CRASH_CORE > + default 0 > + help > + This is used as the default kdump reserved memory size in MB. > + crashkernel=X kernel cmdline can overwrite this value. > + > config HAVE_IMA_KEXEC > bool > > @@ -143,6 +144,24 @@ static int __init parse_crashkernel_simp > return 0; > } > > +static int __init get_crashkernel_default(unsigned long long system_ram, > + unsigned long long *size) > +{ > + unsigned long long sz = CONFIG_CRASHKERNEL_DEFAULT_MB; > + unsigned long long thres = CONFIG_CRASHKERNEL_DEFAULT_THRESHOLD_MB; > + > + thres *= SZ_1M; > + sz *= SZ_1M; > + > + if (sz >= system_ram || system_ram < thres) { > + pr_debug("crashkernel default size can not be used.\n"); > + return -EINVAL; In other words, if (system_ram <= CONFIG_CRASHKERNEL_DEFAULT_MB || system_ram < CONFIG_CRASHKERNEL_DEFAULT_THRESHOLD_MB) fail; yes? How come? What's happening here? Perhaps a (good) explanatory comment is needed. And clearer Kconfig text. All confused :(
