Crash command: kmem -S, -P, -f <address>

[srivathsa729]

Hi, I would like to volunteer for this: drgn Crash Compatibility Mode (view).

[osandov]

Thanks! I'd recommend doing these one at a time since they're all pretty separate.

I'll just copy the notes from the draft issue so I can replace it with this issue:

https://crash-utility.github.io/help_pages/kmem.html

-S shows more slab allocator internals (per-CPU structures, including CPU slabs and partial slabs and per-node structures, including partial and full [if available] slabs, free/allocated for each slab). We'd need helpers for all of these.

-P treats the address as physical (and the command also checks for physical addresses by default, too). It's trivial to map this back to the direct mapped virtual address, but this also seems to identify vmapped physical pages, which is trickier. It doesn't seem to work for the physical address of symbols or pages.

-f <address> theoretically identifies pages on the free list, but I couldn't get it to work. We could probably make identify_address() identify free pages by checking PageBuddy(), but that would require checking the page type, which is a can of macro worms on old kernels.