From 9feedc9d831e18ae6d0d15aa562e5e46ba53647b Mon Sep 17 00:00:00 2001 From: Jiang Liu Date: Wed, 12 Dec 2012 13:52:12 -0800 Subject: mm: introduce new field "managed_pages" to struct zone Currently a zone's present_pages is calcuated as below, which is inaccurate and may cause trouble to memory hotplug. spanned_pages - absent_pages - memmap_pages - dma_reserve. During fixing bugs caused by inaccurate zone->present_pages, we found zone->present_pages has been abused. The field zone->present_pages may have different meanings in different contexts: 1) pages existing in a zone. 2) pages managed by the buddy system. For more discussions about the issue, please refer to: http://lkml.org/lkml/2012/11/5/866 https://patchwork.kernel.org/patch/1346751/ This patchset tries to introduce a new field named "managed_pages" to struct zone, which counts "pages managed by the buddy system". And revert zone->present_pages to count "physical pages existing in a zone", which also keep in consistence with pgdat->node_present_pages. We will set an initial value for zone->managed_pages in function free_area_init_core() and will adjust it later if the initial value is inaccurate. For DMA/normal zones, the initial value is set to: (spanned_pages - absent_pages - memmap_pages - dma_reserve) Later zone->managed_pages will be adjusted to the accurate value when the bootmem allocator frees all free pages to the buddy system in function free_all_bootmem_node() and free_all_bootmem(). The bootmem allocator doesn't touch highmem pages, so highmem zones' managed_pages is set to the accurate value "spanned_pages - absent_pages" in function free_area_init_core() and won't be updated anymore. This patch also adds a new field "managed_pages" to /proc/zoneinfo and sysrq showmem. [akpm@linux-foundation.org: small comment tweaks] Signed-off-by: Jiang Liu Cc: Wen Congyang Cc: David Rientjes Cc: Maciej Rutecki Tested-by: Chris Clayton Cc: "Rafael J . Wysocki" Cc: Mel Gorman Cc: Minchan Kim Cc: KAMEZAWA Hiroyuki Cc: Michal Hocko Cc: Jianguo Wu Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mmzone.h | 41 ++++++++++++++++++++++++++++++++++------- 1 file changed, 34 insertions(+), 7 deletions(-) (limited to 'include/linux/mmzone.h') diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 0c0b1d6..cd55dad 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -460,17 +460,44 @@ struct zone { unsigned long zone_start_pfn; /* - * zone_start_pfn, spanned_pages and present_pages are all - * protected by span_seqlock. It is a seqlock because it has - * to be read outside of zone->lock, and it is done in the main - * allocator path. But, it is written quite infrequently. + * spanned_pages is the total pages spanned by the zone, including + * holes, which is calculated as: + * spanned_pages = zone_end_pfn - zone_start_pfn; * - * The lock is declared along with zone->lock because it is + * present_pages is physical pages existing within the zone, which + * is calculated as: + * present_pages = spanned_pages - absent_pages(pags in holes); + * + * managed_pages is present pages managed by the buddy system, which + * is calculated as (reserved_pages includes pages allocated by the + * bootmem allocator): + * managed_pages = present_pages - reserved_pages; + * + * So present_pages may be used by memory hotplug or memory power + * management logic to figure out unmanaged pages by checking + * (present_pages - managed_pages). And managed_pages should be used + * by page allocator and vm scanner to calculate all kinds of watermarks + * and thresholds. + * + * Locking rules: + * + * zone_start_pfn and spanned_pages are protected by span_seqlock. + * It is a seqlock because it has to be read outside of zone->lock, + * and it is done in the main allocator path. But, it is written + * quite infrequently. + * + * The span_seq lock is declared along with zone->lock because it is * frequently read in proximity to zone->lock. It's good to * give them a chance of being in the same cacheline. + * + * Write access to present_pages and managed_pages at runtime should + * be protected by lock_memory_hotplug()/unlock_memory_hotplug(). + * Any reader who can't tolerant drift of present_pages and + * managed_pages should hold memory hotplug lock to get a stable value. */ - unsigned long spanned_pages; /* total size, including holes */ - unsigned long present_pages; /* amount of memory (excluding holes) */ + unsigned long spanned_pages; + unsigned long present_pages; + unsigned long managed_pages; /* * rarely used fields: -- cgit v1.1