Re: [Lsf-pc] [LSF/MM ATTEND] memory allocation scope

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Thu, 2018-02-15 at 15:48 +0100, Michal Hocko wrote:
> On Wed 14-02-18 16:51:53, Goldwyn Rodrigues wrote:
> > 
> > 
> > Discussion with the memory folks towards scope based allocation
> > I am working on converting some of the GFP_NOFS memory allocation
> > calls to new scope API [1]. While other allocation types (noio,
> > nofs, noreclaim) are covered. Are there plans for identifying scope
> > of GFP_ATOMIC allocations? This should cover most (if not all) of
> > the allocation scope.
> 
> There was no explicit request for that but I can see how some users
> might want it. I would have to double check but maybe this would
> allow vmalloc(GFP_ATOMIC). There were some users but most of them
> could have been changed in some way so the motivation is not very
> large.

We have to be careful about that: most GFP_ATOMIC allocations are in
drivers and may be for DMA'able memory. A We can't currently use vmalloc
memory for DMA to kernel via block because bio_map_kern() uses
virt_to_page() which assumes offset mapping. A The latter is fixable,
obviously, but is it worth fixing? A Very few GFP_ATOMIC allocations in
drivers will be for large chunks.

James

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