Re: upcoming kerneloops.org item: get_page_from_freelist

[Pekka Enberg]

Hi Linus,

On Wed, 24 Jun 2009, Andrew Morton wrote:
>>
>> hm, I didn't know that slub could fall back to lower-order allocations
>> like that.  Neat.

On Wed, Jun 24, 2009 at 9:42 PM, Linus
Torvalds<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> Slab doesn't do it, though. So we still need to get rid of the "order-1"
> warning, at least (slab_break_gfp_order).
>
>> What's the expected value of s->min in allocate_slab()?  In what
>> situations would it be >0?
>
> For slub, s->min has an order of just "get_order(size)" (ie the minimum
> order to fit an object).
>
> For slab, the logic is different, but if I read the code correctly it
> boils down to the minimum order, except that order-1 is accepted instead
> of order-0 (strictly speaking, that only happens if you have more than
> 64MB of RAM). With no fallback.
>
> And it's quite reasonable to expect to be able to do small kmalloc's
> without failing.
>
> So I'd suggest just doing this..

Acked-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>

That said, I do think we ought to fix SLUB not to use __GFP_FAIL for
the higher order allocation regardless of this patch.

                                Pekka
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