the cost of vmalloc

[Mulyadi Santosa]

Hi :)

On Sat, Sep 10, 2011 at 08:16, Zheng Da <zhengda1936 at gmail.com> wrote:
> Hello,
>
> I need to allocate fairly a large piece of memory, about 128KB or
> 256KB.

128 K? Are you sure? That doesn't sound too big for me...but I might
be wrong here..... if you say 4 megabyte, now that's big...

>I tried to use kmalloc, and it sometimes fails, but vmalloc in
> this case usually still work.

easy to guess, vmalloc doesn't care if it's not physically
contigous...only virtually contigous

> But I'm not sure how costly vmalloc is. As far as I know, vmalloc
> needs to change the page table, and thus might need to invalidate TLB.
> It seems quite expensive. If it is, maybe I can allocate memory with
> kmalloc first, and then try to use vmalloc if kmalloc fails. Any
> suggestions?

invalidating page table, at some point yes. Also searching non
physically contigous could be hard too. But again, this is your last
resort to gain such a large memory area.

just my 2 cents idea...

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com