On 9/21/21 6:13 PM, Nicolas Saenz Julienne wrote: > This series introduces an alternative locking scheme around mm/swap.c's per-cpu > LRU pagevec caches and mm/page_alloc.c's per-cpu page lists which will allow > for remote CPUs to drain them. Currently, only a local CPU is permitted to > change its per-cpu lists, and it's expected to do so, on-demand, whenever a > process demands it (by means of queueing an drain task on the local CPU). Most > systems will handle this promptly, but it'll cause problems for NOHZ_FULL CPUs > that can't take any sort of interruption without breaking their functional > guarantees (latency, bandwidth, etc...). Having a way for these processes to > remotely drain the lists themselves will make co-existing with isolated CPUs > possible, at the cost of more constraining locks. > > Fortunately for non-NOHZ_FULL users, the alternative locking scheme and remote > drain code are conditional to a static key which is disabled by default. This > guarantees minimal functional or performance regressions. The feature will only > be enabled if NOHZ_FULL's initialization process was successful. > > This work is based on a previous series by Thomas Gleixner, Anna-Maria > Gleixner, and Sebastian Andrzej Siewior[1]. These days the pcplist protection is done by local_lock, which solved the RT concerns. Probably a stupid/infeasible idea, but maybe what you want to achieve could be more generally solved at the local_lock level? That on NOHZ_FULL CPUs, local_locks could have this mode where they could synchronize with remote cpus? > [1] https://patchwork.kernel.org/project/linux-mm/patch/20190424111208.24459-3-bigeasy@xxxxxxxxxxxxx/ > > Nicolas Saenz Julienne (6): > mm/swap: Introduce lru_cpu_needs_drain() > mm/swap: Introduce alternative per-cpu LRU cache locking > mm/swap: Allow remote LRU cache draining > mm/page_alloc: Introduce alternative per-cpu list locking > mm/page_alloc: Allow remote per-cpu page list draining > sched/isolation: Enable 'remote_pcpu_cache_access' on NOHZ_FULL > systems > > kernel/sched/isolation.c | 9 +- > mm/internal.h | 2 + > mm/page_alloc.c | 111 ++++++++++++++++----- > mm/swap.c | 202 ++++++++++++++++++++++++++++++--------- > 4 files changed, 253 insertions(+), 71 deletions(-) >
