Messages in this thread | | | Date | Mon, 18 Jun 2007 13:42:30 +0200 (CEST) | From | Jan Engelhardt <> | Subject | Re: the memset operation on a automatic array variable can be removed by data Initialization |
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On Jun 18 2007 00:43, Denis Cheng wrote: >Subject: the memset operation on a automatic array variable can be removed by > data Initialization > >--- arch/x86_64/mm/init.c 2007-06-07 10:08:04.000000000 +0800 >+++ /tmp/init.c 2007-06-18 14:43:15.000000000 +0800 >@@ -406,8 +406,7 @@ void __cpuinit zap_low_mappings(int cpu) > #ifndef CONFIG_NUMA > void __init paging_init(void) > { >- unsigned long max_zone_pfns[MAX_NR_ZONES]; >- memset(max_zone_pfns, 0, sizeof(max_zone_pfns)); >+ unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
The cost is the same. "= {0}" is transformed into a bunch of movs, or a rep mov, (At least for x86), so is equivalent to memset (which will get transformed to __builtin_memset anyway). So I wonder what this really buys.
And, you do not even need the zero. Just write ...[MAX_NR_ZONES] = {};
> max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN; > max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN; > max_zone_pfns[ZONE_NORMAL] = end_pfn;
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