From 01cefaef40c48c714b7476e62781230993e10dbf Mon Sep 17 00:00:00 2001 From: Jiang Liu Date: Wed, 12 Dec 2012 13:52:19 -0800 Subject: [PATCH] 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: Jiang Liu Cc: Wen Congyang Cc: David Rientjes Cc: Maciej Rutecki Cc: Chris Clayton Cc: "Rafael J . Wysocki" Cc: Mel Gorman Cc: Minchan Kim Cc: KAMEZAWA Hiroyuki Cc: Michal Hocko Tested-by: Jianguo Wu Cc: Dave Hansen Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0b6a6d04300a..d187988e2b56 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -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; -- 2.20.1