On Fri, 13 Oct 2017 13:32:12 -0400 Pavel Tatashin [off-list ref] wrote:

vmemmap_alloc_block() will no longer zero the block, so zero memory
at its call sites for everything except struct pages.  Struct page memory
is zero'd by struct page initialization.

Replace allocators in sprase-vmemmap to use the non-zeroing version. So,
we will get the performance improvement by zeroing the memory in parallel
when struct pages are zeroed.

Add struct page zeroing as a part of initialization of other fields in
__init_single_page().

This single thread performance collected on: Intel(R) Xeon(R) CPU E7-8895
v3 @ 2.60GHz with 1T of memory (268400646 pages in 8 nodes):

                         BASE            FIX
sparse_init     11.244671836s   0.007199623s
zone_sizes_init  4.879775891s   8.355182299s
                  --------------------------
Total           16.124447727s   8.362381922s

sparse_init is where memory for struct pages is zeroed, and the zeroing
part is moved later in this patch into __init_single_page(), which is
called from zone_sizes_init().

x86_64 allmodconfig:

WARNING: vmlinux.o(.text+0x29d099): Section mismatch in reference from the function T.1331() to the function .meminit.text:vmemmap_alloc_block()
The function T.1331() references
the function __meminit vmemmap_alloc_block().
This is often because T.1331 lacks a __meminit 
annotation or the annotation of vmemmap_alloc_block is wrong.

From a quick scan it's unclear to me why this is happening.  Maybe

gcc-4.4.4 decided to create an out-of-line version of
vmemmap_alloc_block_zero() for some reason.

Anyway.  I see no reason to publish vmemmap_alloc_block_zero() to the
whole world when it's only used in sparse-vmemmap.c.  The below fixes
the section mismatch:

--- a/include/linux/mm.h~mm-stop-zeroing-memory-during-allocation-in-vmemmap-fix
+++ a/include/linux/mm.h

@@ -2529,17 +2529,6 @@ static inline void *vmemmap_alloc_block_
 	return __vmemmap_alloc_block_buf(size, node, NULL);
 }
 
-static inline void *vmemmap_alloc_block_zero(unsigned long size, int node)
-{
-	void *p = vmemmap_alloc_block(size, node);
-
-	if (!p)
-		return NULL;
-	memset(p, 0, size);
-
-	return p;
-}
-
 void vmemmap_verify(pte_t *, int, unsigned long, unsigned long);
 int vmemmap_populate_basepages(unsigned long start, unsigned long end,
 			       int node);
--- a/mm/sparse-vmemmap.c~mm-stop-zeroing-memory-during-allocation-in-vmemmap-fix
+++ a/mm/sparse-vmemmap.c

@@ -178,6 +178,17 @@ pte_t * __meminit vmemmap_pte_populate(p
 	return pte;
 }
 
+static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
+{
+	void *p = vmemmap_alloc_block(size, node);
+
+	if (!p)
+		return NULL;
+	memset(p, 0, size);
+
+	return p;
+}
+
 pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
 {
 	pmd_t *pmd = pmd_offset(pud, addr);

_