Re: [PATCH 12/30] mm: memory reserve management

Hi Peter,

On Thu, 2008-07-24 at 16:00 +0200, Peter Zijlstra wrote:

+/*
+ * alloc wrappers
+ */
+

Hmm, I'm not sure I like the use of __kmalloc_track_caller() (even
though you do add the wrappers for SLUB). The functions really are SLAB
internals so I'd prefer to see kmalloc_reserve() moved to the
allocators.

+void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip,
+			 struct mem_reserve *res, int *emerg)
+{

This function could use some comments...

+	void *obj;
+	gfp_t gfp;
+
+	gfp = flags | __GFP_NOMEMALLOC | __GFP_NOWARN;
+	obj = __kmalloc_node_track_caller(size, gfp, node, ip);
+
+	if (obj || !(gfp_to_alloc_flags(flags) & ALLOC_NO_WATERMARKS))
+		goto out;
+
+	if (res && !mem_reserve_kmalloc_charge(res, size)) {
+		if (!(flags & __GFP_WAIT))
+			goto out;
+
+		wait_event(res->waitqueue,
+				mem_reserve_kmalloc_charge(res, size));
+
+		obj = __kmalloc_node_track_caller(size, gfp, node, ip);
+		if (obj) {
+			mem_reserve_kmalloc_charge(res, -size);

Why do we discharge here?

+			goto out;
+		}

If the allocation fails, we try again (but nothing has changed, right?).
Why?

+	}
+
+	obj = __kmalloc_node_track_caller(size, flags, node, ip);
+	WARN_ON(!obj);

Why don't we discharge from the reserve here if !obj?

+	if (emerg)
+		*emerg |= 1;
+
+out:
+	return obj;
+}
+
+void __kfree_reserve(void *obj, struct mem_reserve *res, int emerg)

I don't see 'emerg' used anywhere.

+{
+	size_t size = ksize(obj);
+
+	kfree(obj);

We're trying to get rid of kfree() so I'd __kfree_reserve() could to
mm/sl?b.c. Matt, thoughts?

+	/*
+	 * ksize gives the full allocated size vs the requested size we used to
+	 * charge; however since we round up to the nearest power of two, this
+	 * should all work nicely.
+	 */
+	mem_reserve_kmalloc_charge(res, -size);
+}