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SubjectRe: [mmotm][experimental][PATCH] coalescing charge
On Thu, 3 Sep 2009 14:17:27 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > =
> > This is a code for batched charging using percpu cache.
> > At charge, memcg charges 64pages and remember it in percpu cache.
> > Because it's cache, drain/flushed if necessary.
> >
> > This version uses public percpu area , not per-memcg percpu area.
> > 2 benefits of public percpu area.
> > 1. Sum of stocked charge in the system is limited to # of cpus
> > not to the number of memcg. This shows better synchonization.
> > 2. drain code for flush/cpuhotplug is very easy (and quick)
> >
> > The most important point of this patch is that we never touch res_counter
> > in fast path. The res_counter is system-wide shared counter which is modified
> > very frequently. We shouldn't touch it as far as we can for avoid false sharing.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> It looks basically good. I'll do some tests with all patches applied.
>
thanks.


> I have some comments inlined.
> > ---
> > mm/memcontrol.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
> > 1 file changed, 88 insertions(+), 5 deletions(-)
> >
> > Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
> > +++ mmotm-2.6.31-Aug27/mm/memcontrol.c
> > @@ -275,6 +275,7 @@ enum charge_type {
> > static void mem_cgroup_get(struct mem_cgroup *mem);
> > static void mem_cgroup_put(struct mem_cgroup *mem);
> > static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
> > +static void drain_all_stock(void);
> >
> > static struct mem_cgroup_per_zone *
> > mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
> > @@ -1136,6 +1137,8 @@ static int mem_cgroup_hierarchical_recla
> > victim = mem_cgroup_select_victim(root_mem);
> > if (victim == root_mem) {
> > loop++;
> > + if (loop >= 1)
> > + drain_all_stock();
> > if (loop >= 2) {
> > /*
> > * If we have not been able to reclaim
> > @@ -1253,6 +1256,79 @@ done:
> > unlock_page_cgroup(pc);
> > }
> >
> > +#define CHARGE_SIZE (64 * PAGE_SIZE)
> > +struct memcg_stock_pcp {
> > + struct mem_cgroup *from;
> > + int charge;
> > +};
> > +DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
> > +
> It might be better to add "static".
>
ok.


> > +static bool consume_stock(struct mem_cgroup *mem)
> > +{
> > + struct memcg_stock_pcp *stock;
> > + bool ret = true;
> > +
> > + stock = &get_cpu_var(memcg_stock);
> > + if (mem == stock->from && stock->charge)
> > + stock->charge -= PAGE_SIZE;
> > + else
> > + ret = false;
> > + put_cpu_var(memcg_stock);
> > + return ret;
> > +}
> > +
> > +static void drain_stock(struct memcg_stock_pcp *stock)
> > +{
> > + struct mem_cgroup *old = stock->from;
> > +
> > + if (stock->charge) {
> > + res_counter_uncharge(&old->res, stock->charge);
> > + if (do_swap_account)
> > + res_counter_uncharge(&old->memsw, stock->charge);
> > + }
> > + stock->from = NULL;
> We must clear stock->charge too.
>
ok.



> > +}
> > +
> > +static void drain_local_stock(struct work_struct *dummy)
> > +{
> > + struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
> > + drain_stock(stock);
> > + put_cpu_var(memcg_stock);
> > +}
> > +
> > +static void refill_stock(struct mem_cgroup *mem, int val)
> > +{
> > + struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
> > +
> > + if (stock->from != mem) {
> > + drain_stock(stock);
> > + stock->from = mem;
> > + }
> > + stock->charge = val;
> > + put_cpu_var(memcg_stock);
> > +}
> > +
> > +static void drain_all_stock(void)
> > +{
> > + schedule_on_each_cpu(drain_local_stock);
> > +}
> > +
> > +static int __cpuinit memcg_stock_cpu_callback(struct notifier_block *nb,
> > + unsigned long action,
> > + void *hcpu)
> > +{
> > +#ifdef CONFIG_HOTPLUG_CPU
> > + int cpu = (unsigned long)*hcpu;
> '*' isn't needed.
>
Hmm, ouch.

> > + struct memcg_stock_pcp *stock;
> > +
> > + if (action != CPU_DEAD)
> > + return NOTIFY_OK;
> > + stock = per_cpu(memcg_stock, cpu);
> '&' is needed.
>
yes..

> > + drain_stock(stock);
> > +#endif
> > + return NOTIFY_OK;
> > +}
> > +
> > /*
> > * Unlike exported interface, "oom" parameter is added. if oom==true,
> > * oom-killer can be invoked.
> > @@ -1288,23 +1364,25 @@ static int __mem_cgroup_try_charge(struc
> > return 0;
> >
> > VM_BUG_ON(css_is_removed(&mem->css));
> > + if (mem_cgroup_is_root(mem))
> > + goto done;
> > + if (consume_stock(mem))
> > + goto charged;
> >
> > while (1) {
> > int ret = 0;
> > unsigned long flags = 0;
> >
> > - if (mem_cgroup_is_root(mem))
> > - goto done;
> > - ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);
> > + ret = res_counter_charge(&mem->res, CHARGE_SIZE, &fail_res);
> > if (likely(!ret)) {
> > if (!do_swap_account)
> > break;
> > - ret = res_counter_charge(&mem->memsw, PAGE_SIZE,
> > + ret = res_counter_charge(&mem->memsw, CHARGE_SIZE,
> > &fail_res);
> > if (likely(!ret))
> > break;
> > /* mem+swap counter fails */
> > - res_counter_uncharge(&mem->res, PAGE_SIZE);
> > + res_counter_uncharge(&mem->res, CHARGE_SIZE);
> > flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> > mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> > memsw);
> > @@ -1342,6 +1420,9 @@ static int __mem_cgroup_try_charge(struc
> > goto nomem;
> > }
> > }
> > + refill_stock(mem, CHARGE_SIZE - PAGE_SIZE);
> > +
> > +charged:
> > /*
> > * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
> > * if they exceeds softlimit.
> > @@ -2448,6 +2529,7 @@ move_account:
> > goto out;
> > /* This is for making all *used* pages to be on LRU. */
> > lru_add_drain_all();
> > + drain_all_stock();
> > ret = 0;
> > for_each_node_state(node, N_HIGH_MEMORY) {
> > for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
> > @@ -3166,6 +3248,7 @@ mem_cgroup_create(struct cgroup_subsys *
> > root_mem_cgroup = mem;
> > if (mem_cgroup_soft_limit_tree_init())
> > goto free_out;
> > + hotcpu_notifier(memcg_stock_cpu_callback, 0);
> >
> We should include cpu.h to use hotcpu_notifier().
>
Ah, I'll check my .config again..

Thanks,
-Kame


> > } else {
> > parent = mem_cgroup_from_cont(cont->parent);
> >
>
>
> Thanks,
> Daisuke Nishimura.
>



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