Hi Kazu,
在 2023/11/30 15:29, HAGIO KAZUHITO(萩尾 一仁) 写道:
On 2023/11/30 16:21, HAGIO KAZUHITO(萩尾 一仁) wrote:
thanks for the patch.
On 2023/11/28 12:41, Huang Shijie wrote:
If the kernel exports the vmmemap then we can use that symbol in
crash to optimize access. vmmemap is just an array of page structs
after all.
This patch tries to get the "vmemmap" from the vmcore file.
If we can use the "vmemmap", use the vmemmap_is_page_ptr to replace
the generic_is_page_ptr().
I recalled that I also did a similar thing for x86_64 [1] in the past..
so it's not so slow on x86_64 and it has valid section check too.
Maybe your vmlinux is not so big as mine(441M)...
[1]
https://github.com/crash-utility/crash/commit/4141373d9de3fea29f5d2b58f60e44bc132726c0
I don't object to add an entry to vmcoreinfo as a way of getting the
vmemmap value. Seems like arm64 has another value from VMEMMAP_START.
but there are some concerns in crash:
- machdep->flags already has VMEMMAP flag. It's used like "if
(IS_SPARSEMEM() && (machdep->flags & VMEMMAP)" e.g. [1]. Adding the new
flag is very confusing and inconsistent.
- Do all architectures have VMEMMAP_VADDR/END values in crash with
CONFIG_SPARSEMEM_VMEMMAP configured?
yes. your concern are right. I found some arch does not support the
VMEMMAP_VADDR/END.
So it is better to add this into ARM64 first. (I use the arm64 machine
all the time..)
we cannot test all archs, so this kind of arch-independent change makes
me nervous. I would like to suggest an arch-specific use first. e.g.
how about making x86_64_is_page_ptr more generic and use it?
I will add arm64 version code. I am not familar with x86, and I do not
have x86 machine for the testing.
so it's better to not change it.
What happens if you use it on arm64? maybe the valid section can check
it with VMEMMAP_VADDR without the vmemmap value. Just an idea though.
hmm sorry, probably this does not work, I missed this.
+ pfn = (addr - vt->vmemmap) / size;
The code is converted by the linux code:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/asm-generic/memory_model.h?h=v6.7-rc3#n38
#define __page_to_pfn(page) (unsigned long)((page) - vmemmap)
So it's correct.
but can VMEMMAP_VADDR and phys_offset can be used to get vmemmap value
on arm64?
On arm64, I can get vmemmap by parsing "memstart_addr".
But I cannot know if CONFIG_SPARSEMEM_VMEMMAP is enabled.
So if the kernel can export "vmemmap", everything become easy.
All the archs supporting the VMEMMAP can benifit from it, such as arm64,
ppc,loongarch,riscv..
Thanks
Huang Shijie
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