Re: [PATCH -mm 5/5] swapcgroup (v3): implement force_empty

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

On Fri, 4 Jul 2008 15:24:23 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> This patch implements force_empty of swapcgroup.
> 
> Currently, it simply uncharges all the charges from the group.
> 
> I think there can be other implementations.
> 
> What I thought are:
> - move all the charges to its parent.
> - unuse(swap in) all the swap charged to the group.
> 
3. move all swap back to memory (see swapoff.)


> But in any case, I think before implementing this way,
> hierarchy and move charges support are needed.
> 
> So I think this is enough for the first step.
> 

I don't think hierarchy/automatic-load-balancer for swap cg is necessary.
Hmm...but handling limit_change (at least, returns -EBUSY) will be necessary.
Do you consider a some magical way to move pages in swap back to memory ?


In general, I like this set but we can't change the limit on demand. (maybe)
(just putting it to TO-DO-List is okay to me.)

Thanks,
-Kame


> 
> Change log
> v2->v3
> - new patch
> 
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> ---
>  include/linux/memcontrol.h |    5 ++++
>  mm/memcontrol.c            |   47 +++++++++++++++++++++++++++++++--------
>  mm/swapfile.c              |   52 +++++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 91 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 1e6eb0c..8c4bad0 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -177,6 +177,7 @@ extern void swap_cgroup_uncharge(struct swap_info_struct *si,
>  				unsigned long offset);
>  extern struct mem_cgroup *page_to_memcg(struct page *page);
>  extern int swap_cgroup_vm_swap_full(struct mem_cgroup *memcg);
> +extern void __swap_cgroup_force_empty(struct mem_cgroup *mem);
>  #else
>  static inline
>  struct mem_cgroup **swap_info_clear_memcg(struct swap_info_struct *p)
> @@ -211,6 +212,10 @@ static inline int swap_cgroup_vm_swap_full(struct mem_cgroup *memcg)
>  {
>  	return 0;
>  }
> +
> +static inline void __swap_cgroup_force_empty(struct mem_cgroup *mem)
> +{
> +}
>  #endif
>  
>  #endif /* _LINUX_MEMCONTROL_H */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 160fca1..f93907c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -826,6 +826,34 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem,
>  	spin_unlock_irqrestore(&mz->lru_lock, flags);
>  }
>  
> +static inline int mem_cgroup_in_use(struct mem_cgroup *mem)
> +{
> +	return mem->res.usage > 0;
> +}
> +
> +static inline int swap_cgroup_in_use(struct mem_cgroup *mem)
> +{
> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
> +	return mem->swap_res.usage > 0;
> +#else
> +	return 0;
> +#endif
> +}
> +
> +static void __mem_cgroup_force_empty(struct mem_cgroup *mem)
> +{
> +	int node, zid;
> +
> +	for_each_node_state(node, N_POSSIBLE)
> +		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> +			struct mem_cgroup_per_zone *mz;
> +			enum lru_list l;
> +			mz = mem_cgroup_zoneinfo(mem, node, zid);
> +			for_each_lru(l)
> +				mem_cgroup_force_empty_list(mem, mz, l);
> +		}
> +}
> +
>  /*
>   * make mem_cgroup's charge to be 0 if there is no task.
>   * This enables deleting this mem_cgroup.
> @@ -833,7 +861,6 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *mem,
>  static int mem_cgroup_force_empty(struct mem_cgroup *mem)
>  {
>  	int ret = -EBUSY;
> -	int node, zid;
>  
>  	css_get(&mem->css);
>  	/*
> @@ -841,18 +868,17 @@ static int mem_cgroup_force_empty(struct mem_cgroup *mem)
>  	 * active_list <-> inactive_list while we don't take a lock.
>  	 * So, we have to do loop here until all lists are empty.
>  	 */
> -	while (mem->res.usage > 0) {
> +	while (mem_cgroup_in_use(mem) || swap_cgroup_in_use(mem)) {
>  		if (atomic_read(&mem->css.cgroup->count) > 0)
>  			goto out;
> -		for_each_node_state(node, N_POSSIBLE)
> -			for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> -				struct mem_cgroup_per_zone *mz;
> -				enum lru_list l;
> -				mz = mem_cgroup_zoneinfo(mem, node, zid);
> -				for_each_lru(l)
> -					mem_cgroup_force_empty_list(mem, mz, l);
> -			}
> +
> +		if (mem_cgroup_in_use(mem))
> +			__mem_cgroup_force_empty(mem);
> +
> +		if (swap_cgroup_in_use(mem))
> +			__swap_cgroup_force_empty(mem);
>  	}
> +
>  	ret = 0;
>  out:
>  	css_put(&mem->css);
> @@ -1289,6 +1315,7 @@ void swap_cgroup_uncharge(struct swap_info_struct *si,
>  	 *    and called swap_entry_free().
>  	 * 2. when this swap entry had been assigned by
>  	 *    get_swap_page_of_type() (via SWSUSP?).
> +	 * 3. force empty can make such entries.
>  	 */
>  	if (mem) {
>  		res_counter_uncharge(&mem->swap_res, PAGE_SIZE);
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6a863bc..2263ae8 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -704,15 +704,30 @@ static int unuse_mm(struct mm_struct *mm,
>  }
>  
>  /*
> + * return the mem_cgroup to which a entry is charged
> + */
> +static inline struct mem_cgroup *entry_to_memcg(swp_entry_t entry)
> +{
> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
> +	return swap_info[swp_type(entry)].memcg[swp_offset(entry)];
> +#else
> +	return NULL;
> +#endif
> +}
> +
> +/*
>   * Scan swap_map from current position to next entry still in use.
> + * If mem is specified, the entry should be charged to it.
>   * Recycle to start on reaching the end, returning 0 when empty.
>   */
>  static unsigned int find_next_to_unuse(struct swap_info_struct *si,
> -					unsigned int prev)
> +					unsigned int prev,
> +					struct mem_cgroup *mem)
>  {
>  	unsigned int max = si->max;
>  	unsigned int i = prev;
>  	int count;
> +	int type = si - swap_info;
>  
>  	/*
>  	 * No need for swap_lock here: we're just looking
> @@ -735,7 +750,8 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
>  			i = 1;
>  		}
>  		count = si->swap_map[i];
> -		if (count && count != SWAP_MAP_BAD)
> +		if (count && count != SWAP_MAP_BAD
> +			&& (!mem || mem == entry_to_memcg(swp_entry(type, i))))
>  			break;
>  	}
>  	return i;
> @@ -782,7 +798,7 @@ static int try_to_unuse(unsigned int type)
>  	 * one pass through swap_map is enough, but not necessarily:
>  	 * there are races when an instance of an entry might be missed.
>  	 */
> -	while ((i = find_next_to_unuse(si, i)) != 0) {
> +	while ((i = find_next_to_unuse(si, i, NULL)) != 0) {
>  		if (signal_pending(current)) {
>  			retval = -EINTR;
>  			break;
> @@ -1923,5 +1939,35 @@ struct mem_cgroup *page_to_memcg(struct page *page)
>  out:
>  	return mem;
>  }
> +
> +/*
> + * uncharge all the entries that are charged to the group.
> + */
> +void __swap_cgroup_force_empty(struct mem_cgroup *mem)
> +{
> +	struct swap_info_struct *p;
> +	int type;
> +
> +	spin_lock(&swap_lock);
> +	for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
> +		p = swap_info + type;
> +
> +		if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
> +			unsigned int i = 0;
> +
> +			spin_unlock(&swap_lock);
> +			while ((i = find_next_to_unuse(p, i, mem)) != 0) {
> +				spin_lock(&swap_lock);
> +				if (p->swap_map[i] && p->memcg[i] == mem)
> +					swap_cgroup_uncharge(p, i);
> +				spin_unlock(&swap_lock);
> +			}
> +			spin_lock(&swap_lock);
> +		}
> +	}
> +	spin_unlock(&swap_lock);
> +
> +	return;
> +}
>  #endif
>  
> 

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