On Thu, Jan 26, 2023 at 08:45:36AM +0100, Michal Hocko wrote: > On Wed 25-01-23 15:22:00, Marcelo Tosatti wrote: > [...] > > Remote draining reduces interruptions whether CPU > > is marked as isolated or not: > > > > - Allows isolated CPUs from benefiting of pcp caching. > > - Removes the interruption to non isolated CPUs. See for example > > > > https://lkml.org/lkml/2022/6/13/2769 > > This is talking about page allocato per cpu caches, right? In this patch > we are talking about memcg pcp caches. Are you sure the same applies > here? Both can stall the users of the drain operation. "Minchan Kim tested this independently and reported; My workload is not NOHZ CPUs but run apps under heavy memory pressure so they goes to direct reclaim and be stuck on drain_all_pages until work on workqueue run." Therefore using a workqueue to drain memcg pcps also depends on the remote CPU executing that work item in time (which can stall the following). No? === 7 3141 mm/memory.c <<wp_page_copy>> if (mem_cgroup_charge(page_folio(new_page), mm, GFP_KERNEL)) 8 4118 mm/memory.c <<do_anonymous_page>> if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL)) 9 4577 mm/memory.c <<do_cow_fault>> if (mem_cgroup_charge(page_folio(vmf->cow_page), vma->vm_mm, 10 621 mm/migrate_device.c <<migrate_vma_insert_page>> if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL)) 11 710 mm/shmem.c <<shmem_add_to_page_cache>> error = mem_cgroup_charge(folio, charge_mm, gfp);
