From c78e93630d15b5f5774213aad9bdc9f52473a89b Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Tue, 12 Nov 2013 15:08:15 -0800 Subject: [PATCH] mm: do not walk all of system memory during show_mem It has been reported on very large machines that show_mem is taking almost 5 minutes to display information. This is a serious problem if there is an OOM storm. The bulk of the cost is in show_mem doing a very expensive PFN walk to give us the following information Total RAM: Also available as totalram_pages Highmem pages: Also available as totalhigh_pages Reserved pages: Can be inferred from the zone structure Shared pages: PFN walk required Unshared pages: PFN walk required Quick pages: Per-cpu walk required Only the shared/unshared pages requires a full PFN walk but that information is useless. It is also inaccurate as page pins of unshared pages would be accounted for as shared. Even if the information was accurate, I'm struggling to think how the shared/unshared information could be useful for debugging OOM conditions. Maybe it was useful before rmap existed when reclaiming shared pages was costly but it is less relevant today. The PFN walk could be optimised a bit but why bother as the information is useless. This patch deletes the PFN walker and infers the total RAM, highmem and reserved pages count from struct zone. It omits the shared/unshared page usage on the grounds that it is useless. It also corrects the reporting of HighMem as HighMem/MovableOnly as ZONE_MOVABLE has similar problems to HighMem with respect to lowmem/highmem exhaustion. Signed-off-by: Mel Gorman Cc: David Rientjes Acked-by: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/show_mem.c | 39 +++++++++++---------------------------- 1 file changed, 11 insertions(+), 28 deletions(-) diff --git a/lib/show_mem.c b/lib/show_mem.c index b7c72311ad0c..5847a4921b8e 100644 --- a/lib/show_mem.c +++ b/lib/show_mem.c @@ -12,8 +12,7 @@ void show_mem(unsigned int filter) { pg_data_t *pgdat; - unsigned long total = 0, reserved = 0, shared = 0, - nonshared = 0, highmem = 0; + unsigned long total = 0, reserved = 0, highmem = 0; printk("Mem-Info:\n"); show_free_areas(filter); @@ -22,43 +21,27 @@ void show_mem(unsigned int filter) return; for_each_online_pgdat(pgdat) { - unsigned long i, flags; + unsigned long flags; + int zoneid; pgdat_resize_lock(pgdat, &flags); - for (i = 0; i < pgdat->node_spanned_pages; i++) { - struct page *page; - unsigned long pfn = pgdat->node_start_pfn + i; - - if (unlikely(!(i % MAX_ORDER_NR_PAGES))) - touch_nmi_watchdog(); - - if (!pfn_valid(pfn)) + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { + struct zone *zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) continue; - page = pfn_to_page(pfn); - - if (PageHighMem(page)) - highmem++; + total += zone->present_pages; + reserved = zone->present_pages - zone->managed_pages; - if (PageReserved(page)) - reserved++; - else if (page_count(page) == 1) - nonshared++; - else if (page_count(page) > 1) - shared += page_count(page) - 1; - - total++; + if (is_highmem_idx(zoneid)) + highmem += zone->present_pages; } pgdat_resize_unlock(pgdat, &flags); } printk("%lu pages RAM\n", total); -#ifdef CONFIG_HIGHMEM - printk("%lu pages HighMem\n", highmem); -#endif + printk("%lu pages HighMem/MovableOnly\n", highmem); printk("%lu pages reserved\n", reserved); - printk("%lu pages shared\n", shared); - printk("%lu pages non-shared\n", nonshared); #ifdef CONFIG_QUICKLIST printk("%lu pages in pagetable cache\n", quicklist_total_size()); -- 2.30.2