On Tue, Nov 06, 2012 at 02:55:06PM -0500, Rik van Riel wrote: > On 11/06/2012 04:14 AM, Mel Gorman wrote: > >It is tricky to quantify the basic cost of automatic NUMA placement in a > >meaningful manner. This patch adds some vmstats that can be used as part > >of a basic costing model. > > > >u = basic unit = sizeof(void *) > >Ca = cost of struct page access = sizeof(struct page) / u > >Cpte = Cost PTE access = Ca > >Cupdate = Cost PTE update = (2 * Cpte) + (2 * Wlock) > > where Cpte is incurred twice for a read and a write and Wlock > > is a constant representing the cost of taking or releasing a > > lock > >Cnumahint = Cost of a minor page fault = some high constant e.g. 1000 > >Cpagerw = Cost to read or write a full page = Ca + PAGE_SIZE/u > >Ci = Cost of page isolation = Ca + Wi > > where Wi is a constant that should reflect the approximate cost > > of the locking operation > >Cpagecopy = Cpagerw + (Cpagerw * Wnuma) + Ci + (Ci * Wnuma) > > where Wnuma is the approximate NUMA factor. 1 is local. 1.2 > > would imply that remote accesses are 20% more expensive > > > >Balancing cost = Cpte * numa_pte_updates + > > Cnumahint * numa_hint_faults + > > Ci * numa_pages_migrated + > > Cpagecopy * numa_pages_migrated > > > >Note that numa_pages_migrated is used as a measure of how many pages > >were isolated even though it would miss pages that failed to migrate. A > >vmstat counter could have been added for it but the isolation cost is > >pretty marginal in comparison to the overall cost so it seemed overkill. > > > >The ideal way to measure automatic placement benefit would be to count > >the number of remote accesses versus local accesses and do something like > > > > benefit = (remote_accesses_before - remove_access_after) * Wnuma > > > >but the information is not readily available. As a workload converges, the > >expection would be that the number of remote numa hints would reduce to 0. > > > > convergence = numa_hint_faults_local / numa_hint_faults > > where this is measured for the last N number of > > numa hints recorded. When the workload is fully > > converged the value is 1. > > > >This can measure if the placement policy is converging and how fast it is > >doing it. > > > >Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > > I'm skipping the ACKing of the policy patches, which > appear to be meant to be placeholders for a "real" > policy. I do expect the MORON policy to disappear or at least change so much it is not recognisable. > However, you have a few more mechanism patches > left in the series, which would be required regardless > of what policy gets merged, so ... > Initially, I had the slow WSS sampling at the end because superficially they could be considered an optimisation and I wanted to avoid sneaking optimisations in. On reflection, the slow WSS sampling is pretty fundamental and I've moved it earlier in the series like so; mm: mempolicy: Add MPOL_MF_LAZY mm: mempolicy: Use _PAGE_NUMA to migrate pages mm: numa: Add fault driven placement and migration mm: sched: numa: Implement constant, per task Working Set Sampling (WSS) rate mm: sched: numa: Implement slow start for working set sampling mm: numa: Add pte updates, hinting and migration stats mm: numa: Migrate on reference policy -- 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>