On Tue, Apr 26, 2011 at 09:37:58PM +1000, NeilBrown wrote:
> On Tue, 26 Apr 2011 08:36:43 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > + /*
> > + * If there are full empty slabs and we were not forced to
> > + * allocate a slab, mark this one !pfmemalloc
> > + */
> > + l3 = cachep->nodelists[numa_mem_id()];
> > + if (!list_empty(&l3->slabs_free) && force_refill) {
> > + struct slab *slabp = virt_to_slab(objp);
> > + slabp->pfmemalloc = false;
> > + clear_obj_pfmemalloc(&objp);
> > + check_ac_pfmemalloc(cachep, ac);
> > + return objp;
> > + }
>
> The comment doesn't match the code. I think you need to remove the words
> "full" and "not" assuming the code is correct which it probably is...
>
I'll fix up the comment, you're right, it's confusing.
> But the code seems to be much more complex than Peter's original, and I don't
> see the gain.
>
You're right, it is more complex.
> Peter's code had only one 'reserved' flag for each kmem_cache.
The reserve was set in a per-cpu structure so there was a "lag" time
before that information was available to other CPUs. Fine on smaller
machines but a bit more of a problem today.
> You seem to
> have one for every slab. I don't see the point.
> It is true that yours is in some sense more fair - but I'm not sure the
> complexity is worth it.
>
More fairness was one of the objects.
> Was there some particular reason you made the change?
>
This version survives under considerably more stress than Peter's
original version did without requiring the additional complexity of
memory reserves.
--
Mel Gorman
SUSE Labs
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