Re: __GFP flags and kmalloc failures

[Pierre Ossman]

Marcelo Tosatti wrote:

> On Tue, Nov 02, 2004 at 04:49:20PM +0100, Pierre Ossman wrote:
>  
>
> > The problem is now that this allocation doesn't always succeed. When it 
> > fails I get:
> >
> > insmod: page allocation failure. order:4, mode:0x11
> >    
>
> This is a big allocation and the kernel is having problem finding such a 
> big page, due to memory fragmentation (as you mention below).
>
> What kernel version are you using?
>  
I'm currently running 2.6.9. No external patches (except for my own 
stuff related to this driver).

> -mm contains a series of patches from Nick which should make the situation 
> better, have you tried it? Currently kswapd doenst honour high order 
> page shortage.
>
>  
No I haven't. Only saw it today and I usually don't use the -mm tree. 
I've gotten the impression it's a bit too bleeding edge for me ;)
What do these patches add to the mix?
I'm also not familiar what the order means. I guess it's some kind of 
priority system? Is there a way I can raise my priority to get access to 
the memory that kswapd actually keeps available?

> > As for solutions I've tried using __GFP_REPEAT which seems to do the 
> > trick. But the double underscore indicates (at least to me) that these 
> > are internal defines that shouldn't be used except for very special 
> > cases. What is the policy about these?
> >    
>
> Its OK to use these flags externally. They might change in future major kernel
> versions though, or even future v2.6 release.  ie its not a stable API.
>  
Is there any other way of increasing the chances of actually getting the 
pages I need? Since it is DMA it needs to be one big block.

Rgds
Pierre
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