Messages in this thread | | | Date | Wed, 24 Jun 2009 11:30:37 -0700 | From | Andrew Morton <> | Subject | Re: upcoming kerneloops.org item: get_page_from_freelist |
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On Wed, 24 Jun 2009 20:53:41 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> Hi Andrew, > > Andrew Morton wrote: > > On Wed, 24 Jun 2009 19:55:24 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote: > > > >> On Wed, Jun 24, 2009 at 7:46 PM, Andrew Morton<akpm@linux-foundation.org> wrote: > >>> Well yes. __Using GFP_NOFAIL on a higher-order allocation is bad. __This > >>> patch is there to find, name, shame, blame and hopefully fix callers. > >>> > >>> A fix for cxgb3 is in the works. __slub's design is a big problem. > >>> > >>> But we'll probably have to revert it for 2.6.31 :( > >> How is SLUB's design a problem here? Can't we just clear GFP_NOFAIL > >> from the higher order allocation and thus force GFP_NOFAIL allocations > >> to use the minimum required order? > > > > That could then lead to the __GFP_NOFAIL allocation attempt returning > > NULL. But the callers cannot handle that and probably don't even test > > for it - this is why they used __GFP_NOFAIL. > > No, the fallback allocation would still use __GFP_NOFAIL so the > semantics are preserved. >
<looks>
hm, I didn't know that slub could fall back to lower-order allocations like that. Neat.
Yes, it looks like that change would improve things. We have had reports before of machines which oomed over an order-1 attempt when there were order-0 pages available. If that were to happen in allocate_slab(__GFP_NOFAIL), things would get ugly and the patch would help.
What's the expected value of s->min in allocate_slab()? In what situations would it be >0?
btw, gcc has in the past made a mess of handling small copy-by-value structs like 'struct kmem_cache_order_objects'. Probably it's improved in recent years, but it'd be worth checking to see if s/struct kmem_cache_order_objects/unsigned long/ generates better code.
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