On 05/21/18 at 12:02pm, Andrew Morton wrote: > On Mon, 21 May 2018 10:53:37 +0800 Dave Young <dyoung@xxxxxxxxxx> 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 <dyoung@xxxxxxxxxx> > > --- > > 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? the first comparison is a sanity check for the default reserved size, if it is bigger than system ram size it is apparently bad: if ( CONFIG_CRASHKERNEL_DEFAULT_MB >= system_ram ) fail; The second comparison is for the threshold setting, it is a designed logic like: if ( system_ram >= CONFIG_CRASHKERNEL_DEFAULT_THRESHOLD_MB ) then go ahead to use the default value of CONFIG_CRASHKERNEL_DEFAULT_MB > > How come? What's happening here? Perhaps a (good) explanatory comment > is needed. And clearer Kconfig text. > > All confused :( Hmm, scratch head~, will think about how to describe it better. If you have any suggestions just let me know :) Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
