On Wed, Jul 13, 2016 at 10:25:04AM +0100, Mel Gorman wrote: > On Wed, Jul 13, 2016 at 11:24:13AM +0900, Minchan Kim wrote: > > If we use sc->reclaim_idx for accounting pgstall, it can increase > > the count on unpopulated zone, for example, movable zone(but > > my system doesn't have movable zone) if allocation request were > > GFP_HIGHUSER_MOVABLE. It doesn't make no sense. > > > > I wanted to track the highest zone allowed by each allocation regardless > of what the zone population state was. Otherwise, consider the following > on a NUMA system > > 1. An allocation request arrives for GFP_HIGHUSER_MOVABLE that stalls > 2. System has two nodes, node 0 with ZONE_NORMAL, node 1 with ZONE_HIGHMEM > 3. If the allocating process is on node 0, the stall is accounted on ZONE_NORMAL > 4. If the allocatinn process is on node 1, the stall is accounted on ZONE_HIGHMEM > > Multiple runs of the same workload on the same machine will see stall > statistics on different zones and renders the stat useless. This is > difficult to analyse because stalls accounted for on ZONE_NORMAL may or > may not be zone-constrained allocations. Fair enough. For the allocstall, it would be better to show the requested zone. > > The patch means that the vmstat accounting and tracepoint data is also > out of sync. One thing I wanted to be able to do was > > 1. Observe that there are alloc stalls on DMA32 or some other low zone > 2. Activate mm_vmscan_direct_reclaim_begin, filter on classzone_idx == > DMA32 and identify the source of the lowmem allocations > > If your patch is applied, I cannot depend on the stall stats any more > and the tracepoint is required to determine if there really any > zone-contrained allocations. It can be *inferred* from the skip stats > but only if such skips occurred and that is not guaranteed. Just a nit: Hmm, can't we omit classzone_idx in mm_vm_scan_direct_begin_template? Because every functions already have gfp_flags so that we can classzone_idx via gfp_zone(gfp_flags) without passing it. > > -- > Mel Gorman > SUSE Labs -- 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>