On Thu, Mar 5, 2020 at 8:41 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, 3 Mar 2020 18:20:58 -0800 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> > Currently reading memory.numa_stat traverses the underlying memcg tree
> > multiple times to accumulate the stats to present the hierarchical view
> > of the memcg tree. However the kernel already maintains the hierarchical
> > view of the stats and use it in memory.stat. Just use the same mechanism
> > in memory.numa_stat as well.
> >
> > I ran a simple benchmark which reads root_mem_cgroup's memory.numa_stat
> > file in the presense of 10000 memcgs. The results are:
> >
> > Without the patch:
> > $ time cat /dev/cgroup/memory/memory.numa_stat > /dev/null
> >
> > real 0m0.700s
> > user 0m0.001s
> > sys 0m0.697s
> >
> > With the patch:
> > $ time cat /dev/cgroup/memory/memory.numa_stat > /dev/null
> >
> > real 0m0.001s
> > user 0m0.001s
> > sys 0m0.000s
> >
>
> Can't you do better than that ;)
>
> >
> > + page_state = tree ? lruvec_page_state : lruvec_page_state_local;
> > ...
> >
> > + page_state = tree ? memcg_page_state : memcg_page_state_local;
> >
>
> All four of these functions are inlined. Taking their address in this
> fashion will force the compiler to generate out-of-line copies.
>
> If we do it the uglier-and-maybe-a-bit-slower way:
>
> --- a/mm/memcontrol.c~memcg-optimize-memorynuma_stat-like-memorystat-fix
> +++ a/mm/memcontrol.c
> @@ -3658,17 +3658,16 @@ static unsigned long mem_cgroup_node_nr_
> struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
> unsigned long nr = 0;
> enum lru_list lru;
> - unsigned long (*page_state)(struct lruvec *lruvec,
> - enum node_stat_item idx);
>
> VM_BUG_ON((unsigned)nid >= nr_node_ids);
>
> - page_state = tree ? lruvec_page_state : lruvec_page_state_local;
> -
> for_each_lru(lru) {
> if (!(BIT(lru) & lru_mask))
> continue;
> - nr += page_state(lruvec, NR_LRU_BASE + lru);
> + if (tree)
> + nr += lruvec_page_state(lruvec, NR_LRU_BASE + lru);
> + else
> + nr += lruvec_page_state_local(lruvec, NR_LRU_BASE + lru);
> }
> return nr;
> }
> @@ -3679,14 +3678,14 @@ static unsigned long mem_cgroup_nr_lru_p
> {
> unsigned long nr = 0;
> enum lru_list lru;
> - unsigned long (*page_state)(struct mem_cgroup *memcg, int idx);
> -
> - page_state = tree ? memcg_page_state : memcg_page_state_local;
>
> for_each_lru(lru) {
> if (!(BIT(lru) & lru_mask))
> continue;
> - nr += page_state(memcg, NR_LRU_BASE + lru);
> + if (tree)
> + nr += memcg_page_state(memcg, NR_LRU_BASE + lru);
> + else
> + nr += memcg_page_state_local(memcg, NR_LRU_BASE + lru);
> }
> return nr;
> }
>
> Then we get:
>
> text data bss dec hex filename
> now: 106705 35641 1024 143370 2300a mm/memcontrol.o
> shakeel: 107111 35657 1024 143792 231b0 mm/memcontrol.o
> shakeel+the-above: 106805 35657 1024 143486 2307e mm/memcontrol.o
>
> Which do we prefer? The 100-byte patch or the 406-byte patch?
I would go with the 100-byte one. The for-loop is just 5 iteration, so
doing a check in each iteration should not be an issue.
Shakeel
