From 20b51af15e014cac63b58a4f8b8b323ac35bccce Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Thu, 2 Sep 2021 14:59:33 -0700 Subject: mm/migrate: add sysfs interface to enable reclaim migration Some method is obviously needed to enable reclaim-based migration. Just like traditional autonuma, there will be some workloads that will benefit like workloads with more "static" configurations where hot pages stay hot and cold pages stay cold. If pages come and go from the hot and cold sets, the benefits of this approach will be more limited. The benefits are truly workload-based and *not* hardware-based. We do not believe that there is a viable threshold where certain hardware configurations should have this mechanism enabled while others do not. To be conservative, earlier work defaulted to disable reclaim- based migration and did not include a mechanism to enable it. This proposes add a new sysfs file /sys/kernel/mm/numa/demotion_enabled as a method to enable it. We are open to any alternative that allows end users to enable this mechanism or disable it if workload harm is detected (just like traditional autonuma). Once this is enabled page demotion may move data to a NUMA node that does not fall into the cpuset of the allocating process. This could be construed to violate the guarantees of cpusets. However, since this is an opt-in mechanism, the assumption is that anyone enabling it is content to relax the guarantees. Link: https://lkml.kernel.org/r/20210721063926.3024591-9-ying.huang@intel.com Link: https://lkml.kernel.org/r/20210715055145.195411-10-ying.huang@intel.com Signed-off-by: Huang Ying Originally-by: Dave Hansen Cc: Michal Hocko Cc: Wei Xu Cc: Yang Shi Cc: Zi Yan Cc: David Rientjes Cc: Dan Williams Cc: David Hildenbrand Cc: Greg Thelen Cc: Keith Busch Cc: Oscar Salvador Cc: Yang Shi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'mm/vmscan.c') diff --git a/mm/vmscan.c b/mm/vmscan.c index 43289f5f8488..2255025f1891 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -524,6 +524,8 @@ static long add_nr_deferred(long nr, struct shrinker *shrinker, static bool can_demote(int nid, struct scan_control *sc) { + if (!numa_demotion_enabled) + return false; if (sc) { if (sc->no_demotion) return false; @@ -534,8 +536,7 @@ static bool can_demote(int nid, struct scan_control *sc) if (next_demotion_node(nid) == NUMA_NO_NODE) return false; - // FIXME: actually enable this later in the series - return false; + return true; } static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, -- cgit