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Date: Tue, 17 Feb 2009 08:54:05 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: linux-mm@...ck.org, Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
Bharata B Rao <bharata@...ibm.com>,
Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
Pavel Emelianov <xemul@...nvz.org>,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Rik van Riel <riel@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][PATCH 3/4] Memory controller soft limit organize cgroups
(v2)
* KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-02-17 10:00:00]:
> > /*
> > + * Cgroups above their limits are maintained in a RB-Tree, independent of
> > + * their hierarchy representation
> > + */
> > +
> > +static struct rb_root mem_cgroup_soft_limit_exceeded_groups;
>
> 37 length variable name seems too long.
>
OK, I'll shorten it
>
> > +static DEFINE_SPINLOCK(memcg_soft_limit_tree_lock);
> > +
> > +/*
> > * The memory controller data structure. The memory controller controls both
> > * page cache and RSS per cgroup. We would eventually like to provide
> > * statistics based on the statistics developed by Rik Van Riel for clock-pro,
> > @@ -176,12 +185,18 @@ struct mem_cgroup {
> >
> > unsigned int swappiness;
> >
> > + struct rb_node mem_cgroup_node;
> > + unsigned long long usage_in_excess;
> > + unsigned long last_tree_update;
> > +
>
> no comment fields.
>
I'll add them, the names are descriptive, but comments always help
> Do usage_in_excess and last_tree_update have what unit? "unsigned long"
> don't tell me anything.
>
>
> > /*
> > * statistics. This must be placed at the end of memcg.
> > */
> > struct mem_cgroup_stat stat;
> > };
> >
> > +#define MEM_CGROUP_TREE_UPDATE_INTERVAL (HZ)
> > +
>
> In general, memory subsystem be considered to shouldn't have timer thing.
> it's because we expect we get 100x times faster machine after 10 year,
> at that time, we expect proper timeout value is changed.
>
Right now, I don't want to overwhelm the system by updating the tree
every time a page is added/removed. So I use an interval to see if we
should update the tree. I am not using any timers per-se.
> Can we make proper stastics, instead?
>
I am not sure I understand your proposal fully
>
> > enum charge_type {
> > MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
> > MEM_CGROUP_CHARGE_TYPE_MAPPED,
> > @@ -214,6 +229,41 @@ 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 mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
> > +{
> > + struct rb_node **p = &mem_cgroup_soft_limit_exceeded_groups.rb_node;
> > + struct rb_node *parent = NULL;
> > + struct mem_cgroup *mem_node;
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> > + while (*p) {
> > + parent = *p;
> > + mem_node = rb_entry(parent, struct mem_cgroup, mem_cgroup_node);
> > + if (mem->usage_in_excess < mem_node->usage_in_excess)
> > + p = &(*p)->rb_left;
> > + /*
> > + * We can't avoid mem cgroups that are over their soft
> > + * limit by the same amount
> > + */
> > + else if (mem->usage_in_excess >= mem_node->usage_in_excess)
> > + p = &(*p)->rb_right;
> > + }
> > + rb_link_node(&mem->mem_cgroup_node, parent, p);
> > + rb_insert_color(&mem->mem_cgroup_node,
> > + &mem_cgroup_soft_limit_exceeded_groups);
> > + mem->last_tree_update = jiffies;
> > + spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
> > +}
>
> I think this function is called from page fault hotpath, right?
> if so, you insert global lock into hotpath!
>
page fault hotpath - the hooks are at the place where we would have
called try_to_free_pages(). We already have global locks per zone and
lock is held for a short time to find and pick the correct memcg for
reclaim.
>
> > +
> > +static void mem_cgroup_remove_exceeded(struct mem_cgroup *mem)
> > +{
> > + unsigned long flags;
> > + spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> > + rb_erase(&mem->mem_cgroup_node, &mem_cgroup_soft_limit_exceeded_groups);
> > + spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
> > +}
> > +
> > static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
> > struct page_cgroup *pc,
> > bool charge)
> > @@ -897,6 +947,39 @@ static void record_last_oom(struct mem_cgroup *mem)
> > mem_cgroup_walk_tree(mem, NULL, record_last_oom_cb);
> > }
> >
> > +static void mem_cgroup_check_and_update_tree(struct mem_cgroup *mem,
> > + bool time_check)
> > +{
> > + unsigned long long prev_usage_in_excess, new_usage_in_excess;
> > + bool updated_tree = false;
> > + unsigned long next_update = 0;
> > + unsigned long flags;
> > +
> > + mem_cgroup_get(mem);
> > + prev_usage_in_excess = mem->usage_in_excess;
> > + new_usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> > +
> > + if (time_check)
> > + next_update = mem->last_tree_update +
> > + MEM_CGROUP_TREE_UPDATE_INTERVAL;
> > + if (new_usage_in_excess && time_after(jiffies, next_update)) {
>
> incorrect time_after() usage. jiffies can round-tripping. then
> time_after(jiffies, 0) don't gurantee to return true.
Not sure I completely understand your comment. Is even
mem_cgroup_oom_called time_before broken?
>
> > + if (prev_usage_in_excess)
> > + mem_cgroup_remove_exceeded(mem);
> > + mem_cgroup_insert_exceeded(mem);
> > + updated_tree = true;
> > + } else if (prev_usage_in_excess && !new_usage_in_excess) {
> > + mem_cgroup_remove_exceeded(mem);
> > + updated_tree = true;
> > + }
> > +
> > + if (updated_tree) {
> > + spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> > + mem->last_tree_update = jiffies;
> > + mem->usage_in_excess = new_usage_in_excess;
> > + spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
> > + }
> > + mem_cgroup_put(mem);
> > +}
> >
> > /*
> > * Unlike exported interface, "oom" parameter is added. if oom==true,
> > @@ -906,9 +989,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
> > gfp_t gfp_mask, struct mem_cgroup **memcg,
> > bool oom)
> > {
> > - struct mem_cgroup *mem, *mem_over_limit;
> > + struct mem_cgroup *mem, *mem_over_limit, *mem_over_soft_limit;
> > int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> > - struct res_counter *fail_res;
> > + struct res_counter *fail_res, *soft_fail_res = NULL;
> >
> > if (unlikely(test_thread_flag(TIF_MEMDIE))) {
> > /* Don't account this! */
> > @@ -938,12 +1021,13 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
> > int ret;
> > bool noswap = false;
> >
> > - ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);
> > + ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res,
> > + &soft_fail_res);
> > if (likely(!ret)) {
> > if (!do_swap_account)
> > break;
> > ret = res_counter_charge(&mem->memsw, PAGE_SIZE,
> > - &fail_res);
> > + &fail_res, NULL);
> > if (likely(!ret))
> > break;
> > /* mem+swap counter fails */
> > @@ -985,6 +1069,13 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
> > goto nomem;
> > }
> > }
> > +
> > + if (soft_fail_res) {
> > + mem_over_soft_limit =
> > + mem_cgroup_from_res_counter(soft_fail_res, res);
> > + mem_cgroup_check_and_update_tree(mem_over_soft_limit, true);
> > + }
> > + mem_cgroup_check_and_update_tree(mem, true);
> > return 0;
> > nomem:
> > css_put(&mem->css);
> > @@ -1422,6 +1513,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> > mz = page_cgroup_zoneinfo(pc);
> > unlock_page_cgroup(pc);
> >
> > + mem_cgroup_check_and_update_tree(mem, true);
> > /* at swapout, this memcg will be accessed to record to swap */
> > if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
> > css_put(&mem->css);
> > @@ -2346,6 +2438,7 @@ static void __mem_cgroup_free(struct mem_cgroup *mem)
> > {
> > int node;
> >
> > + mem_cgroup_check_and_update_tree(mem, false);
> > free_css_id(&mem_cgroup_subsys, &mem->css);
> >
> > for_each_node_state(node, N_POSSIBLE)
> > @@ -2412,6 +2505,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> > if (cont->parent == NULL) {
> > enable_swap_cgroup();
> > parent = NULL;
> > + mem_cgroup_soft_limit_exceeded_groups = RB_ROOT;
> > } else {
> > parent = mem_cgroup_from_cont(cont->parent);
> > mem->use_hierarchy = parent->use_hierarchy;
> > @@ -2432,6 +2526,8 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> > res_counter_init(&mem->memsw, NULL);
> > }
> > mem->last_scanned_child = 0;
> > + mem->usage_in_excess = 0;
> > + mem->last_tree_update = 0; /* Yes, time begins at 0 here */
> > spin_lock_init(&mem->reclaim_param_lock);
> >
> > if (parent)
> >
>
Thanks for the review!
--
Balbir
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