Re: [PATCH] fix unused/stale swap cache handling on memcg v3

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

On Mon, 23 Mar 2009 14:04:19 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> > Nice clean-up here :)
> > 
> Thanks, I'll send a cleanup patch for this part later.
> 
Thank you, I'll look into.

> > > @@ -1359,18 +1373,40 @@ charge_cur_mm:
> > >  	return __mem_cgroup_try_charge(mm, mask, ptr, true);
> > >  }
> > >  
> > > -void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
> > > +static void
> > > +__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
> > > +					enum charge_type ctype)
> > >  {
> > > -	struct page_cgroup *pc;
> > > +	unsigned long flags;
> > > +	struct zone *zone = page_zone(page);
> > > +	struct page_cgroup *pc = lookup_page_cgroup(page);
> > > +	int locked = 0;
> > >  
> > >  	if (mem_cgroup_disabled())
> > >  		return;
> > >  	if (!ptr)
> > >  		return;
> > > -	pc = lookup_page_cgroup(page);
> > > -	mem_cgroup_lru_del_before_commit_swapcache(page);
> > > -	__mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
> > > -	mem_cgroup_lru_add_after_commit_swapcache(page);
> > > +
> > > +	/*
> > > +	 * Forget old LRU when this page_cgroup is *not* used. This Used bit
> > > +	 * is guarded by lock_page() because the page is SwapCache.
> > > +	 * If this pc is on orphan LRU, it is also removed from orphan LRU here.
> > > +	 */
> > > +	if (!PageCgroupUsed(pc)) {
> > > +		locked = 1;
> > > +		spin_lock_irqsave(&zone->lru_lock, flags);
> > > +		mem_cgroup_del_lru_list(page, page_lru(page));
> > > +	}
> > Maybe nice. I tried to use lock_page_cgroup() in add_list but I can't ;(
> > I think this works well. But I wonder...why you have to check PageCgroupUsed() ?
> > And is it correct ? Removing PageCgroupUsed() bit check is nice.
> > (This will be "usually returns true" check, anyway)
> > 
> I've just copied lru_del_before_commit_swapcache.
> 
ya, considering now, it seems to be silly quick-hack.

> As you say, this check will return false only in (C) case in memcg_test.txt,
> and even in (C) case calling mem_cgroup_del_lru_list(and mem_cgroup_add_lru_list later)
> would be no problem.
> 
> OK, I'll remove this check.
> 
Thanks,

> This is the updated version(w/o cache_charge cleanup).
> 
> BTW, Should I merge reclaim part based on your patch and post it ?
> 
I think not necessary. keeping changes minimum is important as BUGFIX.
We can visit here again when new -RC stage starts.

no problem from my review.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Thank you very much!
-Kame


> 
> Thanks,
> Daisuke Nishimura.
> ===
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  include/linux/page_cgroup.h |    5 ++
>  mm/memcontrol.c             |  137 +++++++++++++++++++++++++++++--------------
>  2 files changed, 97 insertions(+), 45 deletions(-)
> 
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 7339c7b..e65e61e 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -26,6 +26,7 @@ enum {
>  	PCG_LOCK,  /* page cgroup is locked */
>  	PCG_CACHE, /* charged as cache */
>  	PCG_USED, /* this object is in use. */
> +	PCG_ORPHAN, /* this is not used from memcg:s view but on global LRU */
>  };
>  
>  #define TESTPCGFLAG(uname, lname)			\
> @@ -46,6 +47,10 @@ TESTPCGFLAG(Cache, CACHE)
>  TESTPCGFLAG(Used, USED)
>  CLEARPCGFLAG(Used, USED)
>  
> +TESTPCGFLAG(Orphan, ORPHAN)
> +SETPCGFLAG(Orphan, ORPHAN)
> +CLEARPCGFLAG(Orphan, ORPHAN)
> +
>  static inline int page_cgroup_nid(struct page_cgroup *pc)
>  {
>  	return page_to_nid(pc->page);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2fc6d6c..3492286 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -371,6 +371,50 @@ static int mem_cgroup_walk_tree(struct mem_cgroup *root, void *data,
>   * When moving account, the page is not on LRU. It's isolated.
>   */
>  
> +/*
> + * Orphan List is a list for page_cgroup which is not free but not under
> + * any cgroup. SwapCache which is prefetched by readahead() is typical type but
> + * there are other corner cases.
> + *
> + * Usually, updates to this list happens when swap cache is readaheaded and
> + * finally used by process.
> + */
> +
> +/* for orphan page_cgroups, updated under zone->lru_lock. */
> +
> +struct orphan_list_node {
> +	struct orphan_list_zone {
> +		struct list_head list;
> +	} zone[MAX_NR_ZONES];
> +};
> +struct orphan_list_node *orphan_list[MAX_NUMNODES] __read_mostly;
> +
> +static inline struct orphan_list_zone *orphan_lru(int nid, int zid)
> +{
> +	/*
> +	 * 2 cases for this BUG_ON(), swapcache is generated while init.
> +	 * or NID should be invalid.
> +	 */
> +	BUG_ON(!orphan_list[nid]);
> +	return  &orphan_list[nid]->zone[zid];
> +}
> +
> +static inline void remove_orphan_list(struct page_cgroup *pc)
> +{
> +	ClearPageCgroupOrphan(pc);
> +	list_del_init(&pc->lru);
> +}
> +
> +static void add_orphan_list(struct page *page, struct page_cgroup *pc)
> +{
> +	struct orphan_list_zone *opl;
> +
> +	SetPageCgroupOrphan(pc);
> +	opl = orphan_lru(page_to_nid(page), page_zonenum(page));
> +	list_add_tail(&pc->lru, &opl->list);
> +}
> +
> +
>  void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
>  {
>  	struct page_cgroup *pc;
> @@ -380,6 +424,14 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
>  	if (mem_cgroup_disabled())
>  		return;
>  	pc = lookup_page_cgroup(page);
> +	/*
> +	 * If the page is SwapCache and already on global LRU, it will be on
> +	 * orphan list. remove here
> +	 */
> +	if (unlikely(PageCgroupOrphan(pc))) {
> +		remove_orphan_list(pc);
> +		return;
> +	}
>  	/* can happen while we handle swapcache. */
>  	if (list_empty(&pc->lru) || !pc->mem_cgroup)
>  		return;
> @@ -433,51 +485,17 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
>  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
>  	 */
>  	smp_rmb();
> -	if (!PageCgroupUsed(pc))
> -		return;
> +	if (!PageCgroupUsed(pc) && !PageCgroupOrphan(pc)) {
> +		/* handle swap cache here */
> +		add_orphan_list(page, pc);
> + 		return;
> +	}
>  
>  	mz = page_cgroup_zoneinfo(pc);
>  	MEM_CGROUP_ZSTAT(mz, lru) += 1;
>  	list_add(&pc->lru, &mz->lists[lru]);
>  }
>  
> -/*
> - * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
> - * lru because the page may.be reused after it's fully uncharged (because of
> - * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
> - * it again. This function is only used to charge SwapCache. It's done under
> - * lock_page and expected that zone->lru_lock is never held.
> - */
> -static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
> -{
> -	unsigned long flags;
> -	struct zone *zone = page_zone(page);
> -	struct page_cgroup *pc = lookup_page_cgroup(page);
> -
> -	spin_lock_irqsave(&zone->lru_lock, flags);
> -	/*
> -	 * Forget old LRU when this page_cgroup is *not* used. This Used bit
> -	 * is guarded by lock_page() because the page is SwapCache.
> -	 */
> -	if (!PageCgroupUsed(pc))
> -		mem_cgroup_del_lru_list(page, page_lru(page));
> -	spin_unlock_irqrestore(&zone->lru_lock, flags);
> -}
> -
> -static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
> -{
> -	unsigned long flags;
> -	struct zone *zone = page_zone(page);
> -	struct page_cgroup *pc = lookup_page_cgroup(page);
> -
> -	spin_lock_irqsave(&zone->lru_lock, flags);
> -	/* link when the page is linked to LRU but page_cgroup isn't */
> -	if (PageLRU(page) && list_empty(&pc->lru))
> -		mem_cgroup_add_lru_list(page, page_lru(page));
> -	spin_unlock_irqrestore(&zone->lru_lock, flags);
> -}
> -
> -
>  void mem_cgroup_move_lists(struct page *page,
>  			   enum lru_list from, enum lru_list to)
>  {
> @@ -784,6 +802,24 @@ static int mem_cgroup_count_children(struct mem_cgroup *mem)
>  	return num;
>  }
>  
> +static __init void init_orphan_lru(void)
> +{
> +	struct orphan_list_node *opl;
> +	int nid, zid;
> +	int size = sizeof(struct orphan_list_node);
> +
> +	for_each_node_state(nid, N_POSSIBLE) {
> +		if (node_state(nid, N_NORMAL_MEMORY))
> +			opl = kmalloc_node(size,  GFP_KERNEL, nid);
> +		else
> +			opl = kmalloc(size, GFP_KERNEL);
> +		BUG_ON(!opl);
> +		for (zid = 0; zid < MAX_NR_ZONES; zid++)
> +			INIT_LIST_HEAD(&opl->zone[zid].list);
> +		orphan_list[nid] = opl;
> +	}
> +}
> +
>  /*
>   * Visit the first child (need not be the first child as per the ordering
>   * of the cgroup list, since we track last_scanned_child) of @mem and use
> @@ -1341,16 +1377,28 @@ static void
>  __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
>  					enum charge_type ctype)
>  {
> -	struct page_cgroup *pc;
> +	unsigned long flags;
> +	struct zone *zone = page_zone(page);
> +	struct page_cgroup *pc = lookup_page_cgroup(page);
>  
>  	if (mem_cgroup_disabled())
>  		return;
>  	if (!ptr)
>  		return;
> -	pc = lookup_page_cgroup(page);
> -	mem_cgroup_lru_del_before_commit_swapcache(page);
> +
> +	/* If this pc is on orphan LRU, it is removed from orphan list here. */
> +	spin_lock_irqsave(&zone->lru_lock, flags);
> +	mem_cgroup_del_lru_list(page, page_lru(page));
> +
> +	/* We should hold zone->lru_lock to protect PCG_ORPHAN. */
> +	VM_BUG_ON(PageCgroupOrphan(pc));
>  	__mem_cgroup_commit_charge(ptr, pc, ctype);
> -	mem_cgroup_lru_add_after_commit_swapcache(page);
> +
> +	/* link when the page is linked to LRU but page_cgroup isn't */
> +	if (PageLRU(page) && list_empty(&pc->lru))
> +		mem_cgroup_add_lru_list(page, page_lru(page));
> +	spin_unlock_irqrestore(&zone->lru_lock, flags);
> +
>  	/*
>  	 * Now swap is on-memory. This means this page may be
>  	 * counted both as mem and swap....double count.
> @@ -1376,8 +1424,6 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
>  		}
>  		rcu_read_unlock();
>  	}
> -	/* add this page(page_cgroup) to the LRU we want. */
> -
>  }
>  
>  void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
> @@ -2438,6 +2484,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	/* root ? */
>  	if (cont->parent == NULL) {
>  		enable_swap_cgroup();
> +		init_orphan_lru();
>  		parent = NULL;
>  	} else {
>  		parent = mem_cgroup_from_cont(cont->parent);
> 

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