Hi Guilherme, On 11/19/20 at 06:56pm, Guilherme Piccoli wrote: > Hi Saeed, thanks for your patch/idea! Comments inline, below. > > On Wed, Nov 18, 2020 at 8:29 PM Saeed Mirzamohammadi > <saeed.mirzamohamm...@oracle.com> wrote: > > > > This adds crashkernel=auto feature to configure reserved memory for > > vmcore creation to both x86 and ARM platforms based on the total memory > > size. > > > > Cc: sta...@vger.kernel.org > > Signed-off-by: John Donnelly <john.p.donne...@oracle.com> > > Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohamm...@oracle.com> > > --- > > Documentation/admin-guide/kdump/kdump.rst | 5 +++++ > > arch/arm64/Kconfig | 26 ++++++++++++++++++++++- > > arch/arm64/configs/defconfig | 1 + > > arch/x86/Kconfig | 26 ++++++++++++++++++++++- > > arch/x86/configs/x86_64_defconfig | 1 + > > kernel/crash_core.c | 20 +++++++++++++++-- > > 6 files changed, 75 insertions(+), 4 deletions(-) > > > > diff --git a/Documentation/admin-guide/kdump/kdump.rst > > b/Documentation/admin-guide/kdump/kdump.rst > > index 75a9dd98e76e..f95a2af64f59 100644 > > --- a/Documentation/admin-guide/kdump/kdump.rst > > +++ b/Documentation/admin-guide/kdump/kdump.rst > > @@ -285,7 +285,12 @@ 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 if you have enough memory. The threshold > > +is 1G on x86_64 and arm64. If your system memory is less than the > > threshold, > > +crashkernel=auto will not reserve memory. The size changes according to > > +the system memory size like below: > > > > + x86_64/arm64: 1G-64G:128M,64G-1T:256M,1T-:512M > > As mentioned in the thread, this was tried before and never got merged > - I'm not sure the all the reasons, but I speculate that a stronger > reason is that it'd likely fail in many cases. I've seen cases of 256G
Yes, there were a few tries, last time I tried to set a default value, I do not think people are strongly against it. We have been using the auto in Red Hat for long time, it does work for most of usual cases like Saeed said in the patch. But I think all of us are aligned it is not possible to satisfy all the user cases. Anyway I also think this is good to have. > servers that require crashkernel=600M (or more), due to the amount of > devices. Also, the minimum nowadays would likely be 96M or more - I'm > looping Cascardo and Dann (Debian/Ubuntu maintainers of kdump stuff) > so they maybe can jump in with even more examples/considerations. Another reason of people have different feeling about the memory requirement is currently distributions are doing different on kdump, especially for the userspace part. Kairui did a lot of work in dracut to reduce the memory requirements in dracut, for example only add dump required kernel modules in 2nd kernel initramfs, also we have a lot of other twicks for dracut to use "hostonly" mode, eg. hostonly multipath configurations will just bring up necessary paths instead of creating all of the multipath devices. > > What we've been trying to do in Ubuntu/Debian is using an estimator > approach [0] - this is purely userspace and tries to infer the amount > of necessary memory a kdump minimal[1] kernel would take. I'm not > -1'ing your approach totally, but I think a bit more consideration is > needed in the ranges, at least accounting the number of devices of the > machine or something like that. There are definitely room to improve and make it better in the future, but I think this is a good start and simple enough proposal for the time being :) > > Cheers, > > > Guilherme > > [0] https://salsa.debian.org/debian/makedumpfile/-/merge_requests/7 > [1] Minimal as having a reduced initrd + "shrinking" parameters (like > nr_cpus=1). > Thanks Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
