Mel Gorman <mgorman@xxxxxxx> writes: > On Fri, Apr 02, 2021 at 04:27:17PM +0800, Huang Ying wrote: >> With NUMA balancing, in hint page fault handler, the faulting page >> will be migrated to the accessing node if necessary. During the >> migration, TLB will be shot down on all CPUs that the process has run >> on recently. Because in the hint page fault handler, the PTE will be >> made accessible before the migration is tried. The overhead of TLB >> shooting down can be high, so it's better to be avoided if possible. >> In fact, if we delay mapping the page until migration, that can be >> avoided. This is what this patch doing. >> >> <SNIP> >> > > Thanks, I think this is ok for Andrew to pick up to see if anything > bisects to this commit but it's a low risk. > > Reviewed-by: Mel Gorman <mgorman@xxxxxxx> > > More notes; > > This is not a universal win given that not all workloads exhibit the > pattern where accesses occur in parallel threads between when a page > is marked accessible and when it is migrated. The impact of the patch > appears to be neutral for those workloads. For workloads that do exhibit > the pattern, there is a small gain with a reduction in interrupts as > advertised unlike v1 of the patch. Further tests are running to confirm > the reduction is in TLB shootdown interrupts but I'm reasonably confident > that will be the case. Gains are typically small and the load described in > the changelog appears to be a best case scenario but a 1-5% gain in some > other workloads is still an improvement. There is still the possibility > that some workloads will unnecessarily stall as a result of the patch > for slightly longer periods of time but that is a relatively low risk > and will be difficult to detect. If I'm wrong, a bisection will find it. Hi, Mel, Thanks! Hi, Andrew, I found that V2 cannot apply on top of latest mmotm, so I send V3 as follows. In case you need it. https://lore.kernel.org/lkml/20210408132236.1175607-1-ying.huang@xxxxxxxxx/ Best Regards, Huang, Ying
