[PATCH] mm: make mem_map allocation continuous.
vmemmap allocation current got
[ffffe20000000000-ffffe200001fffff] PMD ->ffff810001400000 on node 0
[ffffe20000200000-ffffe200003fffff] PMD ->ffff810001800000 on node 0
[ffffe20000400000-ffffe200005fffff] PMD ->ffff810001c00000 on node 0
[ffffe20000600000-ffffe200007fffff] PMD ->ffff810002000000 on node 0
[ffffe20000800000-ffffe200009fffff] PMD ->ffff810002400000 on node 0
...
there is 2M hole between them.
the rootcause is that usemap (24 bytes) will be allocated after every 2M
mem_map. and it will push next vmemmap (2M) to next align (2M).
solution:
try to allocate mem_map continously.
after patch, will get
[ffffe20000000000-ffffe200001fffff] PMD ->ffff810001400000 on node 0
[ffffe20000200000-ffffe200003fffff] PMD ->ffff810001600000 on node 0
[ffffe20000400000-ffffe200005fffff] PMD ->ffff810001800000 on node 0
[ffffe20000600000-ffffe200007fffff] PMD ->ffff810001a00000 on node 0
[ffffe20000800000-ffffe200009fffff] PMD ->ffff810001c00000 on node 0
...
and usemap will share in page because of they are allocated continuously too.
sparse_early_usemap_alloc: usemap = ffff810024e00000 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00080 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00100 size = 24
sparse_early_usemap_alloc: usemap = ffff810024e00180 size = 24
...
so we make the bootmem allocation more compact and use less memory for usemap.
Signed-off-by: Yinghai Lu <[email protected]>
Index: linux-2.6/mm/sparse.c
===================================================================
--- linux-2.6.orig/mm/sparse.c
+++ linux-2.6/mm/sparse.c
@@ -285,6 +286,8 @@ struct page __init *sparse_early_mem_map
return NULL;
}
+/* section_map pointer array is 64k */
+static __initdata struct page *section_map[NR_MEM_SECTIONS];
/*
* Allocate the accumulated non-linear sections, allocate a mem_map
* for each and record the physical to section mapping.
@@ -295,14 +298,29 @@ void __init sparse_init(void)
struct page *map;
unsigned long *usemap;
+ /*
+ * map is using big page (aka 2M in x86 64 bit)
+ * usemap is less one page (aka 24 bytes)
+ * so alloc 2M (with 2M align) and 24 bytes in turn will
+ * make next 2M slip to one more 2M later.
+ * then in big system, the memmory will have a lot hole...
+ * here try to allocate 2M pages continously.
+ */
for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
if (!present_section_nr(pnum))
continue;
+ section_map[pnum] = sparse_early_mem_map_alloc(pnum);
+ }
- map = sparse_early_mem_map_alloc(pnum);
- if (!map)
+
+ for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
+ if (!present_section_nr(pnum))
continue;
+ map = section_map[pnum];
+ if (!map)
+ continue;
+
usemap = sparse_early_usemap_alloc(pnum);
if (!usemap)
continue;