On Tue, Apr 26, 2011 at 09:37:58PM +1000, NeilBrown wrote:

On Tue, 26 Apr 2011 08:36:43 +0100 Mel Gorman [off-list ref] wrote:

quoted

+		/*
+		 * 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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