Message-Id: <20081015093203.fba93c35.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 15 Oct 2008 09:32:03 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] memcg:  charge-commit-cancel

On Tue, 14 Oct 2008 15:12:43 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> On Fri, 10 Oct 2008 18:01:50 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > There is a small race in do_swap_page(). When the page swapped-in is charged,
> > the mapcount can be greater than 0. But, at the same time some process (shares
> > it ) call unmap and make mapcount 1->0 and the page is uncharged.
> > 
> >       CPUA 			CPUB
> >        mapcount == 1.
> >    (1) charge if mapcount==0     zap_pte_range()
> >                                 (2) mapcount 1 => 0.
> > 			        (3) uncharge(). (success)
> >    (4) set page'rmap()
> >        mapcoint 0=>1
> > 
> > Then, this swap page's account is leaked.
> > 
> > For fixing this, I added a new interface.
> >   - precharge
> >    account to res_counter by PAGE_SIZE and try to free pages if necessary.
> >   - commit	
> >    register page_cgroup and add to LRU if necessary.
> >   - cancel
> >    uncharge PAGE_SIZE because of do_swap_page failure.
> > 
> > 
> >      CPUA              
> >   (1) charge (always)
> >   (2) set page's rmap (mapcount > 0)
> >   (3) commit charge was necessary or not after set_pte().
> > 
> > This protocol uses PCG_USED bit on page_cgroup for avoiding over accounting.
> > Usual mem_cgroup_charge_common() does precharge -> commit at a time.
> > 
> > And this patch also adds following function to clarify all charges.
> > 
> >   - mem_cgroup_newpage_charge() ....replacement for mem_cgroup_charge()
> > 	called against newly allocated anon pages.
> > 
> >   - mem_cgroup_charge_migrate_fixup()
> >         called only from remove_migration_ptes().
> > 	we'll have to rewrite this later.(this patch just keeps old behavior)
> > 	This function will be removed by additional patch to make migration
> > 	clearer.
> > 
> > Good for clarify "what we does"
> > 
> > Then, we have 4 following charge points.
> >   - newpage
> >   - swapin
> >   - add-to-cache.
> >   - migration.
> > 
> > precharge/commit/cancel can be used for other places,
> >  - shmem, (and other places need precharge.)
> >  - move_account(force_empty) etc...
> >  - migration.
> > 
> > we'll revisit later.
> > 
> > Changelog v5 -> v6:
> >  - added newpage_charge() and migrate_fixup().
> >  - renamed  functions for swap-in from "swap" to "swapin"
> >  - add more precise description.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> >  include/linux/memcontrol.h |   35 +++++++++-
> >  mm/memcontrol.c            |  151 +++++++++++++++++++++++++++++++++++----------
> >  mm/memory.c                |   12 ++-
> >  mm/migrate.c               |    2 
> >  mm/swapfile.c              |    6 +
> >  5 files changed, 165 insertions(+), 41 deletions(-)
> > 
> > Index: mmotm-2.6.27-rc8+/include/linux/memcontrol.h
> > ===================================================================
> > --- mmotm-2.6.27-rc8+.orig/include/linux/memcontrol.h
> > +++ mmotm-2.6.27-rc8+/include/linux/memcontrol.h
> > @@ -27,8 +27,17 @@ struct mm_struct;
> >  
> >  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> >  
> > -extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> > +extern int mem_cgroup_newpage_charge(struct page *page, struct mm_struct *mm,
> >  				gfp_t gfp_mask);
> > +extern int mem_cgroup_charge_migrate_fixup(struct page *page,
> > +				struct mm_struct *mm, gfp_t gfp_mask);
> > +/* for swap handling */
> > +extern int mem_cgroup_try_charge(struct mm_struct *mm,
> > +		gfp_t gfp_mask, struct mem_cgroup **ptr);
> > +extern void mem_cgroup_commit_charge_swapin(struct page *page,
> > +					struct mem_cgroup *ptr);
> > +extern void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr);
> > +
> >  extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> >  					gfp_t gfp_mask);
> >  extern void mem_cgroup_move_lists(struct page *page, enum lru_list lru);
> > @@ -71,7 +80,9 @@ extern long mem_cgroup_calc_reclaim(stru
> >  
> >  
> >  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> > -static inline int mem_cgroup_charge(struct page *page,
> > +struct mem_cgroup;
> > +
> > +static inline int mem_cgroup_newpage_charge(struct page *page,
> >  					struct mm_struct *mm, gfp_t gfp_mask)
> >  {
> >  	return 0;
> > @@ -83,6 +94,26 @@ static inline int mem_cgroup_cache_charg
> >  	return 0;
> >  }
> >  
> > +static inline int mem_cgroup_charge_migrate_fixup(struct page *page,
> > +					struct mm_struct *mm, gfp_t gfp_mask)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int mem_cgroup_try_charge(struct mm_struct *mm,
> > +				gfp_t gfp_mask, struct mem_cgroup **ptr)
> > +{
> > +	return 0;
> > +}
> > +
> > +static void mem_cgroup_commit_charge_swapin(struct page *page,
> > +					  struct mem_cgroup *ptr)
> > +{
> > +}
> > +static void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr)
> > +{
> > +}
> > +
> >  static inline void mem_cgroup_uncharge_page(struct page *page)
> >  {
> >  }
> > Index: mmotm-2.6.27-rc8+/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-2.6.27-rc8+.orig/mm/memcontrol.c
> > +++ mmotm-2.6.27-rc8+/mm/memcontrol.c
> > @@ -467,35 +467,31 @@ unsigned long mem_cgroup_isolate_pages(u
> >  	return nr_taken;
> >  }
> >  
> > -/*
> > - * Charge the memory controller for page usage.
> > - * Return
> > - * 0 if the charge was successful
> > - * < 0 if the cgroup is over its limit
> > +
> > +/**
> > + * mem_cgroup_try_charge - get charge of PAGE_SIZE.
> > + * @mm: an mm_struct which is charged against. (when *memcg is NULL)
> > + * @gfp_mask: gfp_mask for reclaim.
> > + * @memcg: a pointer to memory cgroup which is charged against.
> > + *
> > + * charge aginst memory cgroup pointed by *memcg. if *memcg == NULL, estimated
> > + * memory cgroup from @mm is got and stored in *memcg.
> > + *
> > + * Retruns 0 if success. -ENOMEM at failure.
> >   */
> > -static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> > -				gfp_t gfp_mask, enum charge_type ctype,
> > -				struct mem_cgroup *memcg)
> > +
> > +int mem_cgroup_try_charge(struct mm_struct *mm,
> > +			gfp_t gfp_mask, struct mem_cgroup **memcg)
> >  {
> >  	struct mem_cgroup *mem;
> > -	struct page_cgroup *pc;
> > -	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> > -	struct mem_cgroup_per_zone *mz;
> > -	unsigned long flags;
> > -
> > -	pc = lookup_page_cgroup(page);
> > -	/* can happen at boot */
> > -	if (unlikely(!pc))
> > -		return 0;
> > -	prefetchw(pc);
> > +	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> >  	/*
> >  	 * We always charge the cgroup the mm_struct belongs to.
> >  	 * The mm_struct's mem_cgroup changes on task migration if the
> >  	 * thread group leader migrates. It's possible that mm is not
> >  	 * set, if so charge the init_mm (happens for pagecache usage).
> >  	 */
> > -
> > -	if (likely(!memcg)) {
> > +	if (likely(!*memcg)) {
> >  		rcu_read_lock();
> >  		mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
> >  		if (unlikely(!mem)) {
> > @@ -506,15 +502,17 @@ static int mem_cgroup_charge_common(stru
> >  		 * For every charge from the cgroup, increment reference count
> >  		 */
> >  		css_get(&mem->css);
> > +		*memcg = mem;
> >  		rcu_read_unlock();
> >  	} else {
> > -		mem = memcg;
> > -		css_get(&memcg->css);
> > +		mem = *memcg;
> > +		css_get(&mem->css);
> >  	}
> >  
> > +
> >  	while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE))) {
> >  		if (!(gfp_mask & __GFP_WAIT))
> > -			goto out;
> > +			goto nomem;
> >  
> >  		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> >  			continue;
> > @@ -531,18 +529,33 @@ static int mem_cgroup_charge_common(stru
> >  
> >  		if (!nr_retries--) {
> >  			mem_cgroup_out_of_memory(mem, gfp_mask);
> > -			goto out;
> > +			goto nomem;
> >  		}
> >  	}
> > +	return 0;
> > +nomem:
> > +	css_put(&mem->css);
> > +	return -ENOMEM;
> > +}
> >  
> > +/*
> > + * commit a charge got by mem_cgroup_try_charge() and makes page_cgroup to be
> > + * USED state. If already USED, uncharge and return.
> > + */
> > +
> > +static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> > +				     struct page_cgroup *pc,
> > +				     enum charge_type ctype)
> > +{
> > +	struct mem_cgroup_per_zone *mz;
> > +	unsigned long flags;
> >  
> mem_cgroup_try_charge may return with memcg=NULL, 
> so __mem_cgroup_commit_charge should handle this case.
> (mem_cgroup_commit_charge_swapin and mem_cgroup_cancel_charge_swapin
> have already handled it.)
> 
Hmm...looks into this again, thanks !


> I acutually have seen a NULL-pointer-dereference BUG caused by this
> in testing previous version.
> 
> >  	lock_page_cgroup(pc);
> >  	if (unlikely(PageCgroupUsed(pc))) {
> >  		unlock_page_cgroup(pc);
> >  		res_counter_uncharge(&mem->res, PAGE_SIZE);
> >  		css_put(&mem->css);
> > -
> > -		goto done;
> > +		return;
> >  	}
> >  	pc->mem_cgroup = mem;
> >  	/*
> > @@ -557,15 +570,39 @@ static int mem_cgroup_charge_common(stru
> >  	__mem_cgroup_add_list(mz, pc);
> >  	spin_unlock_irqrestore(&mz->lru_lock, flags);
> >  	unlock_page_cgroup(pc);
> > +}
> >  
> > -done:
> > +/*
> > + * Charge the memory controller for page usage.
> > + * Return
> > + * 0 if the charge was successful
> > + * < 0 if the cgroup is over its limit
> > + */
> > +static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
> > +				gfp_t gfp_mask, enum charge_type ctype,
> > +				struct mem_cgroup *memcg)
> > +{
> > +	struct mem_cgroup *mem;
> > +	struct page_cgroup *pc;
> > +	int ret;
> > +
> > +	pc = lookup_page_cgroup(page);
> > +	/* can happen at boot */
> > +	if (unlikely(!pc))
> > +		return 0;
> > +	prefetchw(pc);
> > +
> > +	mem = memcg;
> > +	ret = mem_cgroup_try_charge(mm, gfp_mask, &mem);
> > +	if (ret)
> > +		return ret;
> > +
> > +	__mem_cgroup_commit_charge(mem, pc, ctype);
> >  	return 0;
> > -out:
> > -	css_put(&mem->css);
> > -	return -ENOMEM;
> >  }
> >  
> > -int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
> > +int mem_cgroup_newpage_charge(struct page *page,
> > +			      struct mm_struct *mm, gfp_t gfp_mask)
> >  {
> >  	if (mem_cgroup_subsys.disabled)
> >  		return 0;
> > @@ -586,6 +623,34 @@ int mem_cgroup_charge(struct page *page,
> >  				MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
> >  }
> >  
> > +/*
> > + * same as mem_cgroup_newpage_charge(), now.
> > + * But what we assume is different from newpage, and this is special case.
> > + * treat this in special function. easy for maintainance.
> > + */
> > +
> > +int mem_cgroup_charge_migrate_fixup(struct page *page,
> > +				struct mm_struct *mm, gfp_t gfp_mask)
> > +{
> > +	if (mem_cgroup_subsys.disabled)
> > +		return 0;
> > +
> > +	if (PageCompound(page))
> > +		return 0;
> > +
> > +	if (page_mapped(page) || (page->mapping && !PageAnon(page)))
> > +		return 0;
> > +
> > +	if (unlikely(!mm))
> > +		mm = &init_mm;
> > +
> > +	return mem_cgroup_charge_common(page, mm, gfp_mask,
> > +				MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
> > +}
> > +
> > +
> > +
> > +
> >  int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> >  				gfp_t gfp_mask)
> >  {
> > @@ -628,6 +693,30 @@ int mem_cgroup_cache_charge(struct page 
> >  				MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
> >  }
> >  
> > +
> > +void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
> > +{
> > +	struct page_cgroup *pc;
> > +
> > +	if (mem_cgroup_subsys.disabled)
> > +		return;
> > +	if (!ptr)
> > +		return;
> > +	pc = lookup_page_cgroup(page);
> > +	__mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
> > +}
> > +
> > +void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
> > +{
> > +	if (mem_cgroup_subsys.disabled)
> > +		return;
> > +	if (!mem)
> > +		return;
> > +	res_counter_uncharge(&mem->res, PAGE_SIZE);
> > +	css_put(&mem->css);
> > +}
> > +
> > +
> >  /*
> >   * uncharge if !page_mapped(page)
> >   */
> > Index: mmotm-2.6.27-rc8+/mm/memory.c
> > ===================================================================
> > --- mmotm-2.6.27-rc8+.orig/mm/memory.c
> > +++ mmotm-2.6.27-rc8+/mm/memory.c
> > @@ -1891,7 +1891,7 @@ gotten:
> >  	cow_user_page(new_page, old_page, address, vma);
> >  	__SetPageUptodate(new_page);
> >  
> > -	if (mem_cgroup_charge(new_page, mm, GFP_KERNEL))
> > +	if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
> >  		goto oom_free_new;
> >  
> >  	/*
> > @@ -2287,6 +2287,7 @@ static int do_swap_page(struct mm_struct
> >  	struct page *page;
> >  	swp_entry_t entry;
> >  	pte_t pte;
> > +	struct mem_cgroup *ptr = NULL;
> >  	int ret = 0;
> >  
> >  	if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
> > @@ -2325,7 +2326,7 @@ static int do_swap_page(struct mm_struct
> >  	lock_page(page);
> >  	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
> >  
> > -	if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> > +	if (mem_cgroup_try_charge(mm, GFP_KERNEL, &ptr) == -ENOMEM) {
> >  		ret = VM_FAULT_OOM;
> >  		unlock_page(page);
> >  		goto out;
> > @@ -2355,6 +2356,7 @@ static int do_swap_page(struct mm_struct
> >  	flush_icache_page(vma, page);
> >  	set_pte_at(mm, address, page_table, pte);
> >  	page_add_anon_rmap(page, vma, address);
> > +	mem_cgroup_commit_charge_swapin(page, ptr);
> >  
> >  	swap_free(entry);
> >  	if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
> > @@ -2375,7 +2377,7 @@ unlock:
> >  out:
> >  	return ret;
> >  out_nomap:
> > -	mem_cgroup_uncharge_page(page);
> > +	mem_cgroup_cancel_charge_swapin(ptr);
> >  	pte_unmap_unlock(page_table, ptl);
> >  	unlock_page(page);
> >  	page_cache_release(page);
> > @@ -2405,7 +2407,7 @@ static int do_anonymous_page(struct mm_s
> >  		goto oom;
> >  	__SetPageUptodate(page);
> >  
> > -	if (mem_cgroup_charge(page, mm, GFP_KERNEL))
> > +	if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))
> >  		goto oom_free_page;
> >  
> >  	entry = mk_pte(page, vma->vm_page_prot);
> > @@ -2498,7 +2500,7 @@ static int __do_fault(struct mm_struct *
> >  				ret = VM_FAULT_OOM;
> >  				goto out;
> >  			}
> > -			if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> > +			if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
> >  				ret = VM_FAULT_OOM;
> >  				page_cache_release(page);
> >  				goto out;
> > Index: mmotm-2.6.27-rc8+/mm/migrate.c
> > ===================================================================
> > --- mmotm-2.6.27-rc8+.orig/mm/migrate.c
> > +++ mmotm-2.6.27-rc8+/mm/migrate.c
> > @@ -133,7 +133,7 @@ static void remove_migration_pte(struct 
> >  	 * be reliable, and this charge can actually fail: oh well, we don't
> >  	 * make the situation any worse by proceeding as if it had succeeded.
> >  	 */
> > -	mem_cgroup_charge(new, mm, GFP_ATOMIC);
> > +	mem_cgroup_charge_migrate_fixup(new, mm, GFP_ATOMIC);
> >  
> >  	get_page(new);
> >  	pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
> > Index: mmotm-2.6.27-rc8+/mm/swapfile.c
> > ===================================================================
> > --- mmotm-2.6.27-rc8+.orig/mm/swapfile.c
> > +++ mmotm-2.6.27-rc8+/mm/swapfile.c
> > @@ -530,17 +530,18 @@ unsigned int count_swap_pages(int type, 
> >  static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
> >  		unsigned long addr, swp_entry_t entry, struct page *page)
> >  {
> > +	struct mem_cgroup *ptr;
> should be initialized to NULL.
> 
exactly.

Thanks,
-Kame

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