On 01/25/19 at 03:08pm, Borislav Petkov wrote: > On Fri, Jan 25, 2019 at 09:45:18PM +0800, Dave Young wrote: > > AFAIK, some people prefer to explictly reserve crash memory at high > > region even if it is possible to reserve at low area. May because > > <4G memory is limited on large server, they want to leave this for other > > use. > > > > Yinghai or Vivek should know more about the history, probably they can > > recall some initial reason. > > Yes, just "prefer" is not good enough. There should be a technical > reason why that's there. Got more about this, actually the thing is for large server with very huge memory and also possible a lot of io devices. The UEFI IO drivers could allocate a lot memory under 896M, so it will leave small room for crashkernel=X Also if the memory is huge, then copying the vmcore will be very slow, people want to use big makedumpfile bitmap buffer, and multithread, then kdump kernel needs more memory, they can choose ,high to get more memory. But for common use cases, if one does not need so much kdump memory reserved he/she can just use crashkernel=X. > > Also, if the user doesn't care, then the code should be free to force > "high" and thus probe a different range for allocation. As Pingfan/me mentioned in another reply, there are two reasons: 1. old kexec-tools can not load kernel to high memory 2. ,high will not work on some systems without some amounts of low memory so it nees reserve extra low memory, it is bad for people who do not want it. > > > Good question, still it may be some historical reason, but it is good to > > make them clear and rethink about it after long time. > > > > I also want to understand, need dig the log more. > > Good idea. That would be a very nice cleanup. :-) Let's review these different parameters: > crashkernel=size[KMG][@offset[KMG]] Did not get the initial commit for this, it should be the very old format, and kernel did not find the base address automatically for the size Other arches still use this, for example mips code seems needs explict @offset, see the function mips_parse_crashkernel in arch/mips/kernel/setup.c Probably there are other arches as well which only support this format. > crashkernel=range1:size1[,range2:size2,...][@offset] This is nice param which can help to dynamically reserve different size depends on system memory. > crashkernel=size[KMG],high > crashkernel=size[KMG],low We have talked about these two. It is not graceful, but seems no way to improve it due to the swiotlb issue. Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
