From: Mike Yoknis Date: Wed, 19 Jun 2013 00:07:03 +0000 (+1000) Subject: mm: memmap_init_zone() performance improvement X-Git-Tag: next-20130619~2^2~330 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=74aef61043d49796cbe776498cf899485b995dd9;p=karo-tx-linux.git 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 --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b5855e545eec..22c528e079a2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3933,8 +3933,11 @@ 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; }