Subject: Re: [PATCH 05/17] arch, mm: pull out allocation of NODE_DATA to generic code

From: Mike Rapoport <[email-masked]>
Date: Fri, 19 Jul 2024 18:34:54 +0300

On Fri, Jul 19, 2024 at 05:07:35PM +0200, David Hildenbrand wrote:
> > > > -	 * Allocate node data.  Try node-local memory and then any node.
> > > > -	 * Never allocate in DMA zone.
> > > > -	 */
> > > > -	nd_pa = memblock_phys_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);
> > > > -	if (!nd_pa) {
> > > > -		pr_err("Cannot find %zu bytes in any node (initial node: %d)\n",
> > > > -		       nd_size, nid);
> > > > -		return;
> > > > -	}
> > > > -	nd = __va(nd_pa);
> > > > -
> > > > -	/* report and initialize */
> > > > -	printk(KERN_INFO "NODE_DATA(%d) allocated [mem %#010Lx-%#010Lx]\n", nid,
> > > > -	       nd_pa, nd_pa + nd_size - 1);
> > > > -	tnid = early_pfn_to_nid(nd_pa >> PAGE_SHIFT);
> > > > -	if (tnid != nid)
> > > > -		printk(KERN_INFO "    NODE_DATA(%d) on node %d\n", nid, tnid);
> > > > -
> > > > -	node_data[nid] = nd;
> > > > -	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
> > > > -
> > > > -	node_set_online(nid);
> > > > -}
> > > > -
> > > >    /**
> > > >     * numa_cleanup_meminfo - Cleanup a numa_meminfo
> > > >     * @mi: numa_meminfo to clean up
> > > > @@ -571,6 +538,7 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
> > > >    			continue;
> > > >    		alloc_node_data(nid);
> > > > +		node_set_online(nid);
> > > >    	}
> > > 
> > > I can spot that we only remove a single node_set_online() call from x86.
> > > 
> > > What about all the other architectures? Will there be any change in behavior
> > > for them? Or do we simply set the nodes online later once more?
> > 
> > On x86 node_set_online() was a part of alloc_node_data() and I moved it
> > outside so it's called right after alloc_node_data(). On other
> > architectures the allocation didn't include that call, so there should be
> > no difference there.
> 
> But won't their arch code try setting the nodes online at a later stage?
> 
> And I think, some architectures only set nodes online conditionally
> (see most other node_set_online() calls).
> 
> Sorry if I'm confused here, but with now unconditional node_set_online(), won't
> we change the behavior of other architectures?

The generic alloc_node_data() does not set the node online:

+/* Allocate NODE_DATA for a node on the local memory */
+void __init alloc_node_data(int nid)
+{
+	const size_t nd_size = roundup(sizeof(pg_data_t), PAGE_SIZE);
+	u64 nd_pa;
+	void *nd;
+	int tnid;
+
+	/* Allocate node data.  Try node-local memory and then any node. */
+	nd_pa = memblock_phys_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);
+	if (!nd_pa)
+		panic("Cannot allocate %zu bytes for node %d data\n",
+		      nd_size, nid);
+	nd = __va(nd_pa);
+
+	/* report and initialize */
+	pr_info("NODE_DATA(%d) allocated [mem %#010Lx-%#010Lx]\n", nid,
+		nd_pa, nd_pa + nd_size - 1);
+	tnid = early_pfn_to_nid(nd_pa >> PAGE_SHIFT);
+	if (tnid != nid)
+		pr_info("    NODE_DATA(%d) on node %d\n", nid, tnid);
+
+	node_data[nid] = nd;
+	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
+}

I might have missed some architecture except x86 that calls
node_set_online() in its alloc_node_data(), but the intention was to leave
that call outside the alloc and explicitly add it after the call to
alloc_node_data() if needed like in x86.

> -- 
> Cheers,
> David / dhildenb

-- 
Sincerely yours,
Mike.