On 4/14/21 5:18 PM, Mel Gorman wrote: > On Wed, Apr 14, 2021 at 02:56:45PM +0200, Vlastimil Babka wrote: >> So it seems that this intermediate assignment to zone counters (using >> atomic_long_set() even) is unnecessary and this could mimic sum_vm_events() that >> just does the summation on a local array? >> > > The atomic is unnecessary for sure but using a local array is > problematic because of your next point. IIUC vm_events seems to do fine without a centralized array and handling CPU hot remove at the sime time ... >> And probably a bit more serious is that vm_events have vm_events_fold_cpu() to >> deal with a cpu going away, but after your patch the stats counted on a cpu just >> disapepar from the sums as it goes offline as there's no such thing for the numa >> counters. >> > > That is a problem I missed. Even if zonestats was preserved on > hot-remove, fold_vm_zone_numa_events would not be reading the CPU so > hotplug events jump all over the place. > > So some periodic folding is necessary. I would still prefer not to do it > by time but it could be done only on overflow or when a file like > /proc/vmstat is read. I'll think about it a bit more and see what I come > up with. ... because vm_events_fold_cpu() seems to simply move the stats from the CPU being offlined to the current one. So the same approach should be enough for NUMA stats? > Thanks! >
