On Tue, Jun 13, 2023 at 04:55:04PM +0800, Baolin Wang wrote: > On some machines, the normal zone can have a large memory hole like > below memory layout, and we can see the range from 0x100000000 to > 0x1800000000 is a hole. So when isolating some migratable pages, the > scanner can meet the hole and it will take more time to skip the large > hole. From my measurement, I can see the isolation scanner will take > 80us ~ 100us to skip the large hole [0x100000000 - 0x1800000000]. > > So adding a new helper to fast search next online memory section > to skip the large hole can help to find next suitable pageblock > efficiently. With this patch, I can see the large hole scanning only > takes < 1us. > > [ 0.000000] Zone ranges: > [ 0.000000] DMA [mem 0x0000000040000000-0x00000000ffffffff] > [ 0.000000] DMA32 empty > [ 0.000000] Normal [mem 0x0000000100000000-0x0000001fa7ffffff] > [ 0.000000] Movable zone start for each node > [ 0.000000] Early memory node ranges > [ 0.000000] node 0: [mem 0x0000000040000000-0x0000000fffffffff] > [ 0.000000] node 0: [mem 0x0000001800000000-0x0000001fa3c7ffff] > [ 0.000000] node 0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff] > [ 0.000000] node 0: [mem 0x0000001fa4000000-0x0000001fa402ffff] > [ 0.000000] node 0: [mem 0x0000001fa4030000-0x0000001fa40effff] > [ 0.000000] node 0: [mem 0x0000001fa40f0000-0x0000001fa73cffff] > [ 0.000000] node 0: [mem 0x0000001fa73d0000-0x0000001fa745ffff] > [ 0.000000] node 0: [mem 0x0000001fa7460000-0x0000001fa746ffff] > [ 0.000000] node 0: [mem 0x0000001fa7470000-0x0000001fa758ffff] > [ 0.000000] node 0: [mem 0x0000001fa7590000-0x0000001fa7ffffff] > > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> This may only be necessary for non-contiguous zones so a check for zone_contiguous could be made but I suspect the saving, if any, would be marginal. However, it's subtle that block_end_pfn can end up in an arbirary location past the end of the zone or past cc->free_pfn. As the "continue" will update cc->migrate_pfn, that might lead to errors in the future. It would be a lot safer to pass in cc->free_pfn and do two things with the value. First, there is no point scanning for a valid online section past cc->free_pfn so terminating after cc->free_pfn may save some cycles. Second, cc->migrate_pfn does not end up with an arbitrary value which is a more defensive approach to any future programming errors. -- Mel Gorman SUSE Labs
