From 20fd7a0bcd1f06db032dbf5c4b26d2201abbd54f Mon Sep 17 00:00:00 2001 From: Mike Yoknis Date: Wed, 20 Mar 2013 15:07:29 +1100 Subject: [PATCH] mm: memmap_init_zone() performance improvement We have what we call an "architectural simulator". It is a computer program that pretends that it is a computer system. We use it to test the firmware before real hardware is available. We have booted Linux on our simulator. As you would expect it takes longer to boot on the simulator than it does on real hardware. With my patch - boot time 41 minutes Without patch - boot time 94 minutes These numbers do not scale linearly to real hardware. But indicate to me a place where Linux can be improved. memmap_init_zone() loops through every Page Frame Number (pfn), including pfn values that are within the gaps between existing memory sections. The unneeded looping will become a boot performance issue when machines configure larger memory ranges that will contain larger and more numerous gaps. The code will skip across invalid pfn values to reduce the number of loops executed. Signed-off-by: Mike Yoknis Cc: Mel Gorman Cc: Johannes Weiner Signed-off-by: Andrew Morton --- mm/page_alloc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 87a4af89e5a0..cc14c7a64ba2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3907,8 +3907,11 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, * exist on hotplugged memory. */ if (context == MEMMAP_EARLY) { - if (!early_pfn_valid(pfn)) + if (!early_pfn_valid(pfn)) { + pfn = ALIGN(pfn + MAX_ORDER_NR_PAGES, + MAX_ORDER_NR_PAGES) - 1; continue; + } if (!early_pfn_in_nid(pfn, nid)) continue; } -- 2.39.5