Commit 01cefaef authored by Jiang Liu's avatar Jiang Liu Committed by Linus Torvalds
Browse files

mm: provide more accurate estimation of pages occupied by memmap 



If SPARSEMEM is enabled, it won't build page structures for non-existing
pages (holes) within a zone, so provide a more accurate estimation of
pages occupied by memmap if there are bigger holes within the zone.

And pages for highmem zones' memmap will be allocated from lowmem, so
charge nr_kernel_pages for that.

[akpm@linux-foundation.org: mark calc_memmap_size __paging_init]
Signed-off-by: default avatarJiang Liu <jiang.liu@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Maciej Rutecki <maciej.rutecki@gmail.com>
Cc: Chris Clayton <chris2553@googlemail.com>
Cc: "Rafael J . Wysocki" <rjw@sisk.pl>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Tested-by: default avatarJianguo Wu <wujianguo@huawei.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 02c0ab68

mm/page_alloc.c

+24 −2
Original line number Diff line number Diff line
@@ -4489,6 +4489,26 @@ void __init set_pageblock_order(void) 


#endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */



static unsigned long __paginginit calc_memmap_size(unsigned long spanned_pages,

						   unsigned long present_pages)

{

	unsigned long pages = spanned_pages;



	/*

	 * Provide a more accurate estimation if there are holes within

	 * the zone and SPARSEMEM is in use. If there are holes within the

	 * zone, each populated memory region may cost us one or two extra

	 * memmap pages due to alignment because memmap pages for each

	 * populated regions may not naturally algined on page boundary.

	 * So the (present_pages >> 4) heuristic is a tradeoff for that.

	 */

	if (spanned_pages > present_pages + (present_pages >> 4) &&

	    IS_ENABLED(CONFIG_SPARSEMEM))

		pages = present_pages;



	return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT;

}



/*

 * Set up the zone data structures:

 *   - mark all pages reserved
@@ -4523,8 +4543,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, 
		 * is used by this zone for memmap. This affects the watermark

		 * and per-cpu initialisations

		 */

		memmap_pages =

			PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;

		memmap_pages = calc_memmap_size(size, realsize);

		if (freesize >= memmap_pages) {

			freesize -= memmap_pages;

			if (memmap_pages)
@@ -4545,6 +4564,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat, 


		if (!is_highmem_idx(j))

			nr_kernel_pages += freesize;

		/* Charge for highmem memmap if there are enough kernel pages */

		else if (nr_kernel_pages > memmap_pages * 2)

			nr_kernel_pages -= memmap_pages;

		nr_all_pages += freesize;



		zone->spanned_pages = size;

CRA Git | Maintained and supported by SUSTech CRA and CCSE