From: Muchun Song songmuchun@bytedance.com
[ Upstream commit b0ba3bff3e7bb6b58bb248bdd2f3d8ad52fd10c3 ]
Patch series "Convert all THP vmstat counters to pages", v6.
This patch series is aimed to convert all THP vmstat counters to pages.
The unit of some vmstat counters are pages, some are bytes, some are HPAGE_PMD_NR, and some are KiB. When we want to expose these vmstat counters to the userspace, we have to know the unit of the vmstat counters is which one. When the unit is bytes or kB, both clearly distinguishable by the B/KB suffix. But for the THP vmstat counters, we may make mistakes.
For example, the below is some bug fix for the THP vmstat counters:
- 7de2e9f195b9 ("mm: memcontrol: correct the NR_ANON_THPS counter of hierarchical memcg") - The first commit in this series ("fix NR_ANON_THPS accounting in charge moving")
This patch series can make the code clear. And make all the unit of the THP vmstat counters in pages. Finally, the unit of the vmstat counters are pages, kB and bytes. The B/KB suffix can tell us that the unit is bytes or kB. The rest which is without suffix are pages.
In this series, I changed the following vmstat counters unit from HPAGE_PMD_NR to pages. However, there is no change to the print format of output to user space.
- NR_ANON_THPS - NR_FILE_THPS - NR_SHMEM_THPS - NR_SHMEM_PMDMAPPED - NR_FILE_PMDMAPPED
Doing this also can make the statistics more accuracy for the THP vmstat counters. This series is consistent with 8f182270dfec ("mm/swap.c: flush lru pvecs on compound page arrival").
Because we use struct per_cpu_nodestat to cache the vmstat counters, which leads to inaccurate statistics especially THP vmstat counters. In the systems with hundreds of processors it can be GBs of memory. For example, for a 96 CPUs system, the threshold is the maximum number of 125. And the per cpu counters can cache 23.4375 GB in total.
The THP page is already a form of batched addition (it will add 512 worth of memory in one go) so skipping the batching seems like sensible. Although every THP stats update overflows the per-cpu counter, resorting to atomic global updates. But it can make the statistics more accuracy for the THP vmstat counters. From this point of view, I think that do this converting is reasonable.
Thanks Hugh for mentioning this. This was inspired by Johannes and Roman. Thanks to them.
This patch (of 7):
The unit of NR_ANON_THPS is HPAGE_PMD_NR already. So it should inc/dec by one rather than nr_pages.
Link: https://lkml.kernel.org/r/20201228164110.2838-1-songmuchun@bytedance.com Link: https://lkml.kernel.org/r/20201228164110.2838-2-songmuchun@bytedance.com Fixes: 468c398233da ("mm: memcontrol: switch to native NR_ANON_THPS counter") Signed-off-by: Muchun Song songmuchun@bytedance.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Pankaj Gupta pankaj.gupta@cloud.ionos.com Reviewed-by: Roman Gushchin guro@fb.com Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Alexey Dobriyan adobriyan@gmail.com Cc: Feng Tang feng.tang@intel.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Hugh Dickins hughd@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: NeilBrown neilb@suse.de Cc: Rafael. J. Wysocki rafael@kernel.org Cc: Randy Dunlap rdunlap@infradead.org Cc: Sami Tolvanen samitolvanen@google.com Cc: Vladimir Davydov vdavydov.dev@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/memcontrol.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a604e69ecfa57..b902948768957 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5668,10 +5668,8 @@ static int mem_cgroup_move_account(struct page *page, __mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages); __mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages); if (PageTransHuge(page)) { - __mod_lruvec_state(from_vec, NR_ANON_THPS, - -nr_pages); - __mod_lruvec_state(to_vec, NR_ANON_THPS, - nr_pages); + __dec_lruvec_state(from_vec, NR_ANON_THPS); + __inc_lruvec_state(to_vec, NR_ANON_THPS); }
}