Re: [patch] mm: rewrite vmap layer

[Johannes Weiner <hannes@saeurebad.de>]

Christoph Lameter <cl@linux-foundation.org> writes:

> Nick Piggin wrote:
>
>>> Or run purge_vma_area_lazy from keventd?
>>  
>> Right. But that's only needed if we want to vmap from irq context too
>> (otherwise we can just do the purge check at vmap time).
>> 
>> Is there any good reason to be able to vmap or vunmap from interrupt
>> time, though?
>
> It would be good to have vunmap work in an interrupt context like other free
> operations. One may hold spinlocks while freeing structure.
>
> vmap from interrupt context would be useful f.e. for general fallback in the
> page allocator to virtually mapped memory if no linear physical memory is
> available (virtualizable compound pages). Without a vmap that can be run in an
> interrupt context we cannot support GFP_ATOMIC allocs there.

I have not much clue about the users but shouldn't you use vmalloc
anyway if you don't need physically contiguous pages?

So while it would be usable then to have both vmap and vunmap work in
atomic context, I don't really get the fallback use case..?

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