Hi Saeed, thanks for your patch/idea! Comments inline, below. On Wed, Nov 18, 2020 at 8:29 PM Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx> 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: stable@xxxxxxxxxxxxxxx > Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx> > Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx> > --- > 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 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. 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. 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).
