Messages in this thread | | | From | HAGIO KAZUHITO(萩尾 一仁) <> | Subject | RE: [PATCH V2 4/6] mm: rename the global section array to mem_sections | Date | Wed, 2 Jun 2021 05:02:31 +0000 |
| |
-----Original Message----- > On 06/02/21 at 01:11am, HAGIO KAZUHITO(萩尾 一仁) wrote: > > -----Original Message----- > > > On Tue, 1 Jun 2021 10:40:09 +0200 David Hildenbrand <david@redhat.com> wrote: > > > > > > > > Thanks, i explained the reason during my last reply. > > > > > Andrew has already picked this patch to -mm tree. > > > > > > > > Just because it's in Andrews tree doesn't mean it will end up upstream. ;) > > > > > > > > Anyhow, no really strong opinion, it's simply unnecessary code churn > > > > that makes bisecting harder without real value IMHO. > > > > > > I think it's a good change - mem_sections refers to multiple instances > > > of a mem_section. Churn is a pain, but that's the price we pay for more > > > readable code. And for having screwed it up originally ;) > > > > From a makedumpfile/crash-utility viewpoint, I don't deny kernel improvement > > and probably the change will not be hard for them to support, but I'd like > > you to remember that the tool users will need to update them for the change. > > As VIM user, I can understand Aisheng's feeling on the mem_section > variable which has the same symbol name as its type. Meanwhile it does > cause makedumpfile/crash having to be changed accordingly. > > Maybe we can carry it when any essential change is needed in both kernel > and makedumpfile/crash around it.
Yes, that is a possible option.
> > > > > The situation where we need to update the tools for new kernels is usual, but > > there are not many cases that they cannot even start session, and this change > > By the way, Kazu, about a case starting session, could you be more specific > or rephrase? I may not get it clearly. Thanks.
As for the current crash, the "mem_section" symbol is used to determine which memory model is used.
if (kernel_symbol_exists("mem_section")) vt->flags |= SPARSEMEM; else if (kernel_symbol_exists("mem_map")) { get_symbol_data("mem_map", sizeof(char *), &vt->mem_map); vt->flags |= FLATMEM; } else vt->flags |= DISCONTIGMEM;
So without updating, crash will assume that the memory model is DISCONTIGMEM, fail during vm_init() and cannot start a session. This is an imitation of the situation though:
- if (kernel_symbol_exists("mem_section")) + if (kernel_symbol_exists("mem_sectionX"))
# crash ... crash: invalid structure member offset: pglist_data_node_mem_map FILE: memory.c LINE: 16420 FUNCTION: dump_memory_nodes()
[/root/bin/crash] error trace: 465304 => 4ac2bf => 4aae19 => 57f4d7
57f4d7: OFFSET_verify+164 4aae19: dump_memory_nodes+5321 4ac2bf: vm_init+4031 465304: main_loop+392
#
Every time a kernel is released, there are some changes that crash can start up with but cannot run a specific crash's command, but a change that crash cannot start up like this case does not occur often.
Also as for makedumpfile, the "SYMBOL(mem_section)" vmcore entry is used to determine the memory model, so it will fail with the following error without an update.
# ./makedumpfile --mem-usage /proc/kcore get_mem_map: Can't distinguish the memory type.
makedumpfile Failed.
Thanks, Kazu
| |