Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

[Konstantin Khlebnikov]

Pekka Enberg wrote:
> On Wed, 20 Jul 2011, Konstantin Khlebnikov wrote:
> > > The changelog isn't that convincing, really. This is kmem_cache_create()
> > > so I'm surprised we'd ever get NULL here in practice. Does this fix some
> > > problem you're seeing? If this is really an issue, I'd blame the page
> > > allocator as GFP_KERNEL should just work.
> >
> > nf_conntrack creates separate slab-cache for each net-namespace,
> > this patch of course not eliminates the chance of failure, but makes it more
> > acceptable.
>
> I'm still surprised you are seeing failures. mm/slab.c hasn't changed
> significantly in a long time. Why hasn't anyone reported this before? I'd
> still be inclined to shift the blame to the page allocator... Mel,
> Christoph?
>
> On Wed, 20 Jul 2011, Konstantin Khlebnikov wrote:
> > struct kmem_size for slub is more compact, it uses pecpu-pointers instead of
> > dumb NR_CPUS-size array.
> > probably better to fix this side...
>
> So how big is 'struct kmem_cache' for your configuration anyway? Fixing
> the per-cpu data structures would be nice but I'm guessing it'll be
> slightly painful for mm/slab.c.

With NR_CPUS=4096 and MAX_NUMNODES=512 its over 9k!
so it require order-4 page, meanwhile PAGE_ALLOC_COSTLY_ORDER is 3

>   			Pekka

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