Re: [PATCH -mmotm 4/7] memcg: improbe performance in moving charge

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Fri, 4 Dec 2009 14:50:49 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> This patch tries to reduce overheads in moving charge by:
> 
> - Instead of calling res_counter_uncharge against the old cgroup in
>   __mem_cgroup_move_account everytime, call res_counter_uncharge at the end of
>   task migration once.
> - Instead of calling res_counter_charge(via __mem_cgroup_try_charge) repeatedly,
>   call res_counter_charge(PAGE_SIZE * count) in can_attach() if possible.
> - Adds a new arg(count) to __css_put and make it decrement the css->refcnt
>   by "count", not 1.
> - Add a new function(__css_get), which takes "count" as a arg and increment
>   the css->recnt by "count".
> - Instead of calling css_get/css_put repeatedly, call new __css_get/__css_put
>   if possible.
> - removed css_get(&to->css) from __mem_cgroup_move_account(callers should have
>   already called css_get), and removed css_put(&to->css) too, which is called by
>   callers of move_account on success of move_account.
> 
> These changes reduces the overhead from 1.7sec to 0.6sec to move charges of 1G
> anonymous memory in my test environment.
> 
> Changelog: 2009/12/04
> - new patch
> 
seems nice in general.


> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  include/linux/cgroup.h |   12 +++-
>  kernel/cgroup.c        |    5 +-
>  mm/memcontrol.c        |  151 +++++++++++++++++++++++++++++++-----------------
>  3 files changed, 109 insertions(+), 59 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index d4cc200..61f75ae 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -75,6 +75,12 @@ enum {
>  	CSS_REMOVED, /* This CSS is dead */
>  };
>  
> +/* Caller must verify that the css is not for root cgroup */
> +static inline void __css_get(struct cgroup_subsys_state *css, int count)
> +{
> +	atomic_add(count, &css->refcnt);
> +}
> +
>  /*
>   * Call css_get() to hold a reference on the css; it can be used
>   * for a reference obtained via:
> @@ -86,7 +92,7 @@ static inline void css_get(struct cgroup_subsys_state *css)
>  {
>  	/* We don't need to reference count the root state */
>  	if (!test_bit(CSS_ROOT, &css->flags))
> -		atomic_inc(&css->refcnt);
> +		__css_get(css, 1);
>  }
>  
>  static inline bool css_is_removed(struct cgroup_subsys_state *css)
> @@ -117,11 +123,11 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
>   * css_get() or css_tryget()
>   */
>  
> -extern void __css_put(struct cgroup_subsys_state *css);
> +extern void __css_put(struct cgroup_subsys_state *css, int count);
>  static inline void css_put(struct cgroup_subsys_state *css)
>  {
>  	if (!test_bit(CSS_ROOT, &css->flags))
> -		__css_put(css);
> +		__css_put(css, 1);
>  }
> 

Maybe it's better to divide cgroup part in other patches. Li or Paul has to review.

 
>  /* bits in struct cgroup flags field */
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index d67d471..44f5924 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -3729,12 +3729,13 @@ static void check_for_release(struct cgroup *cgrp)
>  	}
>  }
>  
> -void __css_put(struct cgroup_subsys_state *css)
> +/*  Caller must verify that the css is not for root cgroup */
> +void __css_put(struct cgroup_subsys_state *css, int count)
>  {
>  	struct cgroup *cgrp = css->cgroup;
>  	int val;
>  	rcu_read_lock();
> -	val = atomic_dec_return(&css->refcnt);
> +	val = atomic_sub_return(count, &css->refcnt);
>  	if (val == 1) {
>  		if (notify_on_release(cgrp)) {
>  			set_bit(CGRP_RELEASABLE, &cgrp->flags);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e38f211..769b85a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -252,6 +252,7 @@ struct move_charge_struct {
>  	struct mem_cgroup *from;
>  	struct mem_cgroup *to;
>  	unsigned long precharge;
> +	unsigned long moved_charge;
>  };
>  static struct move_charge_struct mc;
>  
> @@ -1532,14 +1533,23 @@ nomem:
>   * This function is for that and do uncharge, put css's refcnt.
>   * gotten by try_charge().
>   */
> -static void mem_cgroup_cancel_charge(struct mem_cgroup *mem)
> +static void __mem_cgroup_cancel_charge(struct mem_cgroup *mem,
> +							unsigned long count)
>  {
>  	if (!mem_cgroup_is_root(mem)) {
> -		res_counter_uncharge(&mem->res, PAGE_SIZE);
> +		res_counter_uncharge(&mem->res, PAGE_SIZE * count);
>  		if (do_swap_account)
> -			res_counter_uncharge(&mem->memsw, PAGE_SIZE);
> +			res_counter_uncharge(&mem->memsw, PAGE_SIZE * count);
> +		VM_BUG_ON(test_bit(CSS_ROOT, &mem->css.flags));
> +		WARN_ON_ONCE(count > INT_MAX);

Hmm. is this WARN_ON necessary ? ...maybe res_counter_uncharge() will catch
this, anyway.

> +		__css_put(&mem->css, (int)count);
>  	}
> -	css_put(&mem->css);
> +	/* we don't need css_put for root */
> +}
> +
> +static void mem_cgroup_cancel_charge(struct mem_cgroup *mem)
> +{
> +	__mem_cgroup_cancel_charge(mem, 1);
>  }
>  
>  /*
> @@ -1645,17 +1655,20 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>   * @pc:	page_cgroup of the page.
>   * @from: mem_cgroup which the page is moved from.
>   * @to:	mem_cgroup which the page is moved to. @from != @to.
> + * @uncharge: whether we should call uncharge and css_put against @from.
>   *
>   * The caller must confirm following.
>   * - page is not on LRU (isolate_page() is useful.)
>   * - the pc is locked, used, and ->mem_cgroup points to @from.
>   *
> - * This function does "uncharge" from old cgroup but doesn't do "charge" to
> - * new cgroup. It should be done by a caller.
> + * This function doesn't do "charge" nor css_get to new cgroup. It should be
> + * done by a caller(__mem_cgroup_try_charge would be usefull). If @uncharge is
> + * true, this function does "uncharge" from old cgroup, but it doesn't if
> + * @uncharge is false, so a caller should do "uncharge".
>   */
>  
>  static void __mem_cgroup_move_account(struct page_cgroup *pc,
> -	struct mem_cgroup *from, struct mem_cgroup *to)
> +	struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
>  {
>  	struct page *page;
>  	int cpu;
> @@ -1668,10 +1681,6 @@ static void __mem_cgroup_move_account(struct page_cgroup *pc,
>  	VM_BUG_ON(!PageCgroupUsed(pc));
>  	VM_BUG_ON(pc->mem_cgroup != from);
>  
> -	if (!mem_cgroup_is_root(from))
> -		res_counter_uncharge(&from->res, PAGE_SIZE);
> -	mem_cgroup_charge_statistics(from, pc, false);
> -
>  	page = pc->page;
>  	if (page_mapped(page) && !PageAnon(page)) {
>  		cpu = smp_processor_id();
> @@ -1687,12 +1696,12 @@ static void __mem_cgroup_move_account(struct page_cgroup *pc,
>  		__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_FILE_MAPPED,
>  						1);
>  	}
> +	mem_cgroup_charge_statistics(from, pc, false);
> +	if (uncharge)
> +		/* This is not "cancel", but cancel_charge does all we need. */
> +		mem_cgroup_cancel_charge(from);
>  
> -	if (do_swap_account && !mem_cgroup_is_root(from))
> -		res_counter_uncharge(&from->memsw, PAGE_SIZE);
> -	css_put(&from->css);
> -
> -	css_get(&to->css);
> +	/* caller should have done css_get */
>  	pc->mem_cgroup = to;
>  	mem_cgroup_charge_statistics(to, pc, true);
>  	/*
> @@ -1709,12 +1718,12 @@ static void __mem_cgroup_move_account(struct page_cgroup *pc,
>   * __mem_cgroup_move_account()
>   */
>  static int mem_cgroup_move_account(struct page_cgroup *pc,
> -				struct mem_cgroup *from, struct mem_cgroup *to)
> +		struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
>  {
>  	int ret = -EINVAL;
>  	lock_page_cgroup(pc);
>  	if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
> -		__mem_cgroup_move_account(pc, from, to);
> +		__mem_cgroup_move_account(pc, from, to, uncharge);
>  		ret = 0;
>  	}
>  	unlock_page_cgroup(pc);
> @@ -1750,11 +1759,9 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
>  	if (ret || !parent)
>  		goto put_back;
>  
> -	ret = mem_cgroup_move_account(pc, child, parent);
> -	if (!ret)
> -		css_put(&parent->css);	/* drop extra refcnt by try_charge() */
> -	else
> -		mem_cgroup_cancel_charge(parent);	/* does css_put */
> +	ret = mem_cgroup_move_account(pc, child, parent, true);
> +	if (ret)
> +		mem_cgroup_cancel_charge(parent);
>  put_back:
>  	putback_lru_page(page);
>  put:
> @@ -3441,16 +3448,57 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
>  }
>  
>  /* Handlers for move charge at task migration. */
> -static int mem_cgroup_do_precharge(void)
> +#define PRECHARGE_COUNT_AT_ONCE	256
> +static int mem_cgroup_do_precharge(unsigned long count)
>  {
> -	int ret = -ENOMEM;
> +	int ret = 0;
> +	int batch_count = PRECHARGE_COUNT_AT_ONCE;
>  	struct mem_cgroup *mem = mc.to;
>  
> -	ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false, NULL);
> -	if (ret || !mem)
> -		return -ENOMEM;
> -
> -	mc.precharge++;
> +	if (mem_cgroup_is_root(mem)) {
> +		mc.precharge += count;
> +		/* we don't need css_get for root */
> +		return ret;
> +	}
> +	/* try to charge at once */
> +	if (count > 1) {
> +		struct res_counter *dummy;
> +		/*
> +		 * "mem" cannot be under rmdir() because we've already checked
> +		 * by cgroup_lock_live_cgroup() that it is not removed and we
> +		 * are still under the same cgroup_mutex. So we can postpone
> +		 * css_get().
> +		 */
> +		if (res_counter_charge(&mem->res, PAGE_SIZE * count, &dummy))
> +			goto one_by_one;

 if (do_swap_account) here.

> +		if (res_counter_charge(&mem->memsw,
> +						PAGE_SIZE * count, &dummy)) {
> +			res_counter_uncharge(&mem->res, PAGE_SIZE * count);
> +			goto one_by_one;
> +		}
> +		mc.precharge += count;
> +		VM_BUG_ON(test_bit(CSS_ROOT, &mem->css.flags));
> +		WARN_ON_ONCE(count > INT_MAX);
> +		__css_get(&mem->css, (int)count);
> +		return ret;
> +	}
> +one_by_one:
> +	/* fall back to one by one charge */
> +	while (!ret && count--) {

!ret check seems unnecessary.
> +		if (signal_pending(current)) {
> +			ret = -EINTR;
> +			break;
> +		}
> +		if (!batch_count--) {
> +			batch_count = PRECHARGE_COUNT_AT_ONCE;
> +			cond_resched();
> +		}
> +		ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem,
> +								false, NULL);
> +		if (ret || !mem)
> +			return -ENOMEM;

returning without uncharge here ?

Thanks,
-Kame

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>