Commit e123dd3f authored Apr 13, 2008 by Yinghai Lu Committed by Ingo Molnar Apr 26, 2008

mm: make mem_map allocation continuous



vmemmap allocation currently has this layout:

 [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
...

note that there is a 2M hole between them - not optimal.

the root cause is that usemap (24 bytes) will be allocated after every 2M
mem_map, and it will push next vmemmap (2M) to the next (2M) alignment.

solution: try to allocate the mem_map continously.

after the patch, we 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
...

which is the ideal layout.

and usemap will share a 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 => mission accomplished ;-)

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 539a5fe2

mm/sparse.c

+29 −3

Original line number	Diff line number	Diff line
		@@ -304,22 +304,48 @@ void __init sparse_init(void)
		unsigned long pnum;
		struct page *map;
		unsigned long *usemap;
		unsigned long **usemap_map;
		int size;

		/*
		* 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 memory will have a lot of holes...
		* here try to allocate 2M pages continously.
		*
		* powerpc need to call sparse_init_one_section right after each
		* sparse_early_mem_map_alloc, so allocate usemap_map at first.
		*/
		size = sizeof(unsigned long ) NR_MEM_SECTIONS;
		usemap_map = alloc_bootmem(size);
		if (!usemap_map)
		panic("can not allocate usemap_map\n");

		for (pnum = 0; pnum < NR_MEM_SECTIONS; pnum++) {
		if (!present_section_nr(pnum))
		continue;
		usemap_map[pnum] = sparse_early_usemap_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;

		usemap = sparse_early_usemap_alloc(pnum);
		usemap = usemap_map[pnum];
		if (!usemap)
		continue;

		map = sparse_early_mem_map_alloc(pnum);
		if (!map)
		continue;

		sparse_init_one_section(__nr_to_section(pnum), pnum, map,
		usemap);
		}

		free_bootmem(__pa(usemap_map), size);
		}

		#ifdef CONFIG_MEMORY_HOTPLUG