Re: low memory problem - pool calls vmem calls uvm calls pool etc.

[David Sainty <dave%dtsp.co.nz@localhost>]

On 04/12/13 01:07, Lars Heidieker wrote:
> The recursion happened due to freeing to the wrong arena. Take a look 
> at the pool_allocator_meta and how vmem recurses. It's one vmem arena 
> (kmem_va_arena) using quantum caches and one (actually two 
> kmem_meta_arena(s) stacked on top of kmem_meta_arena) for meta 
> allocations eg pool_allocator_meta those arenas are stacked up on one 
> arena without quatum caching (kmem_arena). So "normal" allocations 
> utilized this cache, but no pool_caches are involved for "meta" 
> allocations. So it might recurse once while switching to allocate via 
> the kmem_meta_arena and from there on no pool_caches are involved. 
> Allocations via vmem_alloc must be freed via vmem_free and vmem_xalloc 
> via vmem_xfree mixing them, at least with quantum caches involved, 
> will lead to inconsistencies. 

It occurs to me that disabling the quantum cache on the meta arenas may 
be specifically to avoid this problem.  But this problem could also, I 
think, be resolved by ensuring that quantum caching is inhibited in 
vmem_free's in, and only in, ENOMEM paths.  Then quantum caching could 
be used for meta arenas too.

Is it worth going to that effort?  Would it be much of a win?