Hi Baoquan, On 05/26/21 at 03:11pm, Baoquan He wrote: > On 05/25/21 at 07:41pm, Dave Young wrote: > > Hi Baoquan, > > > @@ -180,7 +191,7 @@ Dump-capture kernel config options (Arch Dependent, i386 and x86_64) > > > > > > CONFIG_SMP=n > > > > > > - (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line > > > + (If CONFIG_SMP=y, then specify nr_cpus=1 on the kernel command line > > > when loading the dump-capture kernel, see section "Load the Dump-capture > > > Kernel".) > > > > This part should be obsolete? Since for X86_64 we can enable smp boot > > with disable_cpu_apicid=X set (see the Notes on loading the dump-capture > > kernel part) So I think no need to disable CONFIG_SMP at all. The > > current RHEL use of nr_cpus=1 is just to save 2nd kernel memory use. > > Keeping them because they are not wrong. Talking about default config, > currently we only care about x86_64 mostly, not sure if we should remove > i386 part too. Anyway, I am fine to remove them and the below > relocatable thing. I also agree it is not wrong :) But I personally think the doc should target for the most common use cases. If CONFIG_SMP=n is not common then we may just describe the default words for CONFIG_SMP=y, and we may add some words for exection cases for example: Specify nr_cpus=1 blabla Note: if CONFIG_SMP is not set then nr_cpus=1 is not needed ... > > > > > Ditto for the text for other arches, not sure if they need update > > though, see if other maintainers can provide inputs.. > > > > > > Otherwise for the CONFIG_RELOCATABLE related part, it may be better to > > update as well? > > ''' quote: > > 3) If one wants to build and use a relocatable kernel, > > Enable "Build a relocatable kernel" support under "Processor type and > > features":: > > > > CONFIG_RELOCATABLE=y > > > > 4) Use a suitable value for "Physical address where the kernel is > > loaded" (under "Processor type and features"). This only appears when > > "kernel crash dumps" is enabled. A suitable value depends upon > > whether kernel is relocatable or not. > > > > If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000 > > This will compile the kernel for physical address 1MB, but given the fact > > kernel is relocatable, it can be run from any physical address hence > > kexec boot loader will load it in memory region reserved for dump-capture > > kernel. > > > > Otherwise it should be the start of memory region reserved for > > second kernel using boot parameter "crashkernel=Y@X". Here X is > > start of memory region reserved for dump-capture kernel. > > Generally X is 16MB (0x1000000). So you can set > > CONFIG_PHYSICAL_START=0x1000000 > > ''' end quote > > > > Since relocatable kernel is used by default now so we may just not describe it as "If one > > want to build with it =y", I feel it should be a corner case instead of > > the default use case. Maybe HPA, Vivek, Eric can provide more opinions since > > they may know more about the background. > > > > > > ... > > > -Boot into System Kernel > > > -======================= > > > + 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 > > > + > > > +3) crashkernel=size,high and crashkernel=size,low > > > + > > > + If memory above 4G is preferred, crashkernel=size,high can be used to > > > + fulfill that. With it, physical memory is allowed to allocate from top, > > > + so could be above 4G if system has more than 4G RAM installed. Otherwise, > > > + memory region will be allocated below 4G if available. > > > + > > > + When crashkernel=X,high is passed, kernel could allocate physical memory > > > + region above 4G, low memory under 4G is needed in this case. There are > > > + three ways to get low memory: > > > + > > > + 1) Kernel will allocate at least 256M memory below 4G automatically > > > + if crashkernel=Y,low is not specified. > > > + 2) Let user specify low memory size instread. > > > + 3) Specified value 0 will disable low memory allocation:: > > > + > > > + crashkernel=0,low > > > + > > > +Boot into System Kernel > > > +----------------------- > > > 1) Update the boot loader (such as grub, yaboot, or lilo) configuration > > > files as necessary. > > > > > > -2) Boot the system kernel with the boot parameter "crashkernel=Y@X", > > > - where Y specifies how much memory to reserve for the dump-capture kernel > > > - and X specifies the beginning of this reserved memory. For example, > > > - "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory > > > - starting at physical address 0x01000000 (16MB) for the dump-capture kernel. > > > +2) Boot the system kernel with the boot parameter "crashkernel=Y@X". > > > > > > On x86 and x86_64, use "crashkernel=64M@16M". > > > > For the recommendation of crashkernel it would be better to drop the > > @16M since most people do not need it? > > It's only an example? Change it as "crashkernel=128M" instead to make it > more helpful? Hmm, it would be better to make the most common use case in default example, and put the corner cases on corner :) > > > > > > > > > @@ -392,7 +432,7 @@ loading dump-capture kernel. > > > > > > For i386, x86_64 and ia64: > > > > > > - "1 irqpoll maxcpus=1 reset_devices" > > > + "1 irqpoll nr_cpus=1 reset_devices" > > > > > > For ppc64: > > > > > > @@ -400,7 +440,7 @@ For ppc64: > > > > > > For s390x: > > > > > > - "1 maxcpus=1 cgroup_disable=memory" > > > + "1 nr_cpus=1 cgroup_disable=memory" > > > > > > For arm: > > > > > > @@ -408,7 +448,7 @@ For arm: > > > > > > For arm64: > > > > > > - "1 maxcpus=1 reset_devices" > > > + "1 nr_cpus=1 reset_devices" > > > > > > Notes on loading the dump-capture kernel: > > > > > > @@ -487,7 +527,12 @@ After the dump-capture kernel is booted, write out the dump file with > > > the following command:: > > > > > > cp /proc/vmcore <dump-file> > > > + scp /proc/vmcore to <user@server>:<path>/%HOST-%DATE/ > > > + > > > +You can also use makedumpfile utility to write out the dump file > > > +with specified options to filter out unwanted contents, e.g:: > > > > > > + core_collector makedumpfile -l --message-level 1 -d 31 > > > > Looks like scp and core_collector usage are based on Fedora/RHEL, but > > since this doc is for generic upstream, it might be better to describe > > it in generic way, eg. (maybe just drop scp) > > makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file> > > scp /proc/vmcore <user@server>:<path>/<dump-file> > > Right, forgot removing core_collector. While scp is also a generic tool? scp is good to have, just it is similar to cp, as these are just examples I'm fine for either. If taking scp then just drop the " to" and %HOST_%DATE/ etc. > > Thanks for reviewing. > Thanks Dave
