What's the difference between kmem_arena and kernel_arena?

[Konstantin Belousov]

On Sat, Sep 20, 2014 at 03:07:30PM +0800, btw at mail.ustc.edu.cn wrote:
> Hi All,
> 
> There are two similar variables declared in vm/vm_kern.h, they are kernel_arena
> and kmem_arena. Both of them are used in kmem_malloc():
> 
>         rv = kmem_back((vmem == kmem_arena) ? kmem_object : kernel_object,
> 
> I'm wondering what's the difference between them. Why both of them are needed?
> I have done a lot of searching, but I still can not find an answer.

Look at their usage.

kmem_arena is used for the kernel malloc() and page-sized uma allocations.
kernel_arena is used by miscellaneous other kernel needs, e.g. for
kernel stacks of threads, as the backing for kva_alloc() etc.
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