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Subject[RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init() to reduce some iteration cycle
Date
During the sparse_init(), it iterate on each possible section. On x86_64,
it would always be (2^19) even there is not much memory. For example, on a
typical 4G machine, it has only (2^5) to (2^6) present sections. This
benefits more on a system with smaller memory.

This patch calculates the last section number from the highest pfn and use
this as the boundary of iteration.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
mm/sparse.c | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 1e168bf2779a..d72f390d9e61 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -468,18 +468,20 @@ void __weak __meminit vmemmap_populate_print_last(void)

/**
* alloc_usemap_and_memmap - memory alloction for pageblock flags and vmemmap
- * @map: usemap_map for pageblock flags or mmap_map for vmemmap
+ * @data: usemap_map for pageblock flags or mmap_map for vmemmap
*/
static void __init alloc_usemap_and_memmap(void (*alloc_func)
(void *, unsigned long, unsigned long,
- unsigned long, int), void *data)
+ unsigned long, int),
+ void *data,
+ unsigned long last_section_nr)
{
unsigned long pnum;
unsigned long map_count;
int nodeid_begin = 0;
unsigned long pnum_begin = 0;

- for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
+ for (pnum = 0; pnum <= last_section_nr; pnum++) {
struct mem_section *ms;

if (!present_section_nr(pnum))
@@ -490,7 +492,7 @@ static void __init alloc_usemap_and_memmap(void (*alloc_func)
break;
}
map_count = 1;
- for (pnum = pnum_begin + 1; pnum < NR_MEM_SECTIONS; pnum++) {
+ for (pnum = pnum_begin + 1; pnum <= last_section_nr; pnum++) {
struct mem_section *ms;
int nodeid;

@@ -503,16 +505,14 @@ static void __init alloc_usemap_and_memmap(void (*alloc_func)
continue;
}
/* ok, we need to take cake of from pnum_begin to pnum - 1*/
- alloc_func(data, pnum_begin, pnum,
- map_count, nodeid_begin);
+ alloc_func(data, pnum_begin, pnum, map_count, nodeid_begin);
/* new start, update count etc*/
nodeid_begin = nodeid;
pnum_begin = pnum;
map_count = 1;
}
/* ok, last chunk */
- alloc_func(data, pnum_begin, NR_MEM_SECTIONS,
- map_count, nodeid_begin);
+ alloc_func(data, pnum_begin, pnum, map_count, nodeid_begin);
}

/*
@@ -526,6 +526,9 @@ void __init sparse_init(void)
unsigned long *usemap;
unsigned long **usemap_map;
int size;
+ unsigned long last_section_nr;
+ int i;
+ unsigned long last_pfn = 0;
#ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
int size2;
struct page **map_map;
@@ -537,6 +540,11 @@ void __init sparse_init(void)
/* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
set_pageblock_order();

+ for_each_mem_pfn_range_rev(i, NUMA_NO_NODE, NULL,
+ &last_pfn, NULL)
+ break;
+ last_section_nr = pfn_to_section_nr(last_pfn);
+
/*
* map is using big page (aka 2M in x86 64 bit)
* usemap is less one page (aka 24 bytes)
@@ -553,7 +561,8 @@ void __init sparse_init(void)
if (!usemap_map)
panic("can not allocate usemap_map\n");
alloc_usemap_and_memmap(sparse_early_usemaps_alloc_node,
- (void *)usemap_map);
+ (void *)usemap_map,
+ last_section_nr);

#ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
size2 = sizeof(struct page *) * NR_MEM_SECTIONS;
@@ -561,10 +570,11 @@ void __init sparse_init(void)
if (!map_map)
panic("can not allocate map_map\n");
alloc_usemap_and_memmap(sparse_early_mem_maps_alloc_node,
- (void *)map_map);
+ (void *)map_map,
+ last_section_nr);
#endif

- for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
+ for (pnum = 0; pnum <= last_section_nr; pnum++) {
if (!present_section_nr(pnum))
continue;

--
2.11.0
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