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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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