On Mon, Dec 21, 2020 at 07:35:31PM +0000, Shaoying Xu wrote: > From: Johannes Weiner <hannes@xxxxxxxxxxx> > > [ Upstream commit a983b5ebee57209c99f68c8327072f25e0e6e3da ] > > We've seen memory.stat reads in top-level cgroups take up to fourteen > seconds during a userspace bug that created tens of thousands of ghost > cgroups pinned by lingering page cache. > > Even with a more reasonable number of cgroups, aggregating memory.stat > is unnecessarily heavy. The complexity is this: > > nr_cgroups * nr_stat_items * nr_possible_cpus > > where the stat items are ~70 at this point. With 128 cgroups and 128 > CPUs - decent, not enormous setups - reading the top-level memory.stat > has to aggregate over a million per-cpu counters. This doesn't scale. > > Instead of spreading the source of truth across all CPUs, use the > per-cpu counters merely to batch updates to shared atomic counters. > > This is the same as the per-cpu stocks we use for charging memory to the > shared atomic page_counters, and also the way the global vmstat counters > are implemented. > > Vmstat has elaborate spilling thresholds that depend on the number of > CPUs, amount of memory, and memory pressure - carefully balancing the > cost of counter updates with the amount of per-cpu error. That's > because the vmstat counters are system-wide, but also used for decisions > inside the kernel (e.g. NR_FREE_PAGES in the allocator). Neither is > true for the memory controller. > > Use the same static batch size we already use for page_counter updates > during charging. The per-cpu error in the stats will be 128k, which is > an acceptable ratio of cores to memory accounting granularity. > > [hannes@xxxxxxxxxxx: fix warning in __this_cpu_xchg() calls] > Link: http://lkml.kernel.org/r/20171201135750.GB8097@xxxxxxxxxxx > Link: http://lkml.kernel.org/r/20171103153336.24044-3-hannes@xxxxxxxxxxx > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx c9019e9: mm: memcontrol: eliminate raw access to stat and event counters > Cc: stable@xxxxxxxxxxxxxxx 2845426: mm: memcontrol: implement lruvec stat functions on top of each other > Cc: stable@xxxxxxxxxxxxxxx > [shaoyi@xxxxxxxxxx: resolved the conflict brought by commit 17ffa29c355658c8e9b19f56cbf0388500ca7905 in mm/memcontrol.c by contextual fix] > Signed-off-by: Shaoying Xu <shaoyi@xxxxxxxxxx> > --- > The excessive complexity in memory.stat reporting was fixed in v4.16 but didn't appear to make it to 4.14 stable. When backporting this patch, there is a small conflict brought by commit 17ffa29c355658c8e9b19f56cbf0388500ca7905 within free_mem_cgroup_per_node_info() of mm/memcontrol.c and can be resolved by contextual fix. > > include/linux/memcontrol.h | 96 +++++++++++++++++++++++++++--------------- > mm/memcontrol.c | 101 +++++++++++++++++++++++---------------------- > 2 files changed, 113 insertions(+), 84 deletions(-) This patch does not apply to the 4.14.y tree, please fix it up and resend it if you wish to see it applied there. thanks, greg k-h
