On 07/06/2020 02:33 PM, David Hildenbrand wrote:

quoted

 	return 0;

@@ -1505,7 +1505,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	int err;
 
 	if (end - start < PAGES_PER_SECTION * sizeof(struct page))
-		err = vmemmap_populate_basepages(start, end, node);
+		err = vmemmap_populate_basepages(start, end, node, NULL);
 	else if (boot_cpu_has(X86_FEATURE_PSE))
 		err = vmemmap_populate_hugepages(start, end, node, altmap);
 	else if (altmap) {

It's somewhat weird that we don't allocate basepages from altmap on x86
(both for sub-sections and without PSE). I wonder if we can simply
unlock that with your change. Especially, also handle the
!X86_FEATURE_PSE case below properly with an altmap.

a) all hw with PMEM has PSE - except special QEMU setups, so nobody
cared to implement. For the sub-section special case, nobody cared about
a handfull of memmap not ending up on the altmap. (but it's still wasted
system memory IIRC).

b) the pagetable overhead for small pages is not-neglectable and might
result in similar issues as solved by the switch to altmap on very huge
PMEM (with small amount of system RAM).

I guess it is due to a).

Hmm, I assume these are some decisions that x86 platform will have to
make going forward in a subsequent patch as the third patch does for
the arm64 platform. But it is clearly beyond the scope of this patch
which never intended to change existing behavior on a given platform.

[...]

quoted

 
-pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node)
+pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
+				       struct vmem_altmap *altmap)
 {
 	pte_t *pte = pte_offset_kernel(pmd, addr);
 	if (pte_none(*pte)) {
 		pte_t entry;
-		void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
+		void *p;
+
+		if (altmap)
+			p = altmap_alloc_block_buf(PAGE_SIZE, altmap);
+		else
+			p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
 		if (!p)
 			return NULL;

I was wondering if

if (altmap)
	p = altmap_alloc_block_buf(PAGE_SIZE, altmap);
if (!p)
	p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
if (!p)
	return NULL

Would make sense. But I guess this isn't really relevant in practice,
because the altmap is usually sized properly.

In general, LGTM.

Okay, I assume that no further changes are required here.

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