On Mon, 18 Mar 2013, Russ Anderson wrote: > When booting on a large memory system, the kernel spends > considerable time in memmap_init_zone() setting up memory zones. > Analysis shows significant time spent in __early_pfn_to_nid(). > > The routine memmap_init_zone() checks each PFN to verify the > nid is valid. __early_pfn_to_nid() sequentially scans the list of > pfn ranges to find the right range and returns the nid. This does > not scale well. On a 4 TB (single rack) system there are 308 > memory ranges to scan. The higher the PFN the more time spent > sequentially spinning through memory ranges. > > Since memmap_init_zone() increments pfn, it will almost always be > looking for the same range as the previous pfn, so check that > range first. If it is in the same range, return that nid. > If not, scan the list as before. > > A 4 TB (single rack) UV1 system takes 512 seconds to get through > the zone code. This performance optimization reduces the time > by 189 seconds, a 36% improvement. > > A 2 TB (single rack) UV2 system goes from 212.7 seconds to 99.8 seconds, > a 112.9 second (53%) reduction. > > Signed-off-by: Russ Anderson <rja@xxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Very nice improvement! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>