Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v6)

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Thu, 11 Mar 2010 18:42:44 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Thu, 11 Mar 2010 18:25:00 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > Then, it's not problem that check pc->mem_cgroup is root cgroup or not
> > without spinlock.
> > ==
> > void mem_cgroup_update_stat(struct page *page, int idx, bool charge)
> > {
> > 	pc = lookup_page_cgroup(page);
> > 	if (unlikely(!pc) || mem_cgroup_is_root(pc->mem_cgroup))
> > 		return;	
> > 	...
> > }
> > ==
> > This can be handle in the same logic of "lock failure" path.
> > And we just do ignore accounting.
> > 
> > There are will be no spinlocks....to do more than this,
> > I think we have to use "struct page" rather than "struct page_cgroup".
> > 
> Hmm..like this ? The bad point of this patch is that this will corrupt FILE_MAPPED
> status in root cgroup. This kind of change is not very good.
> So, one way is to use this kind of function only for new parameters. Hmm.
IMHO, if we disable accounting file stats in root cgroup, it would be better
not to show them in memory.stat to avoid confusing users.
But, hmm, I think accounting them in root cgroup isn't so meaningless.
Isn't making mem_cgroup_has_dirty_limit() return false in case of root cgroup enough?

> ==
> 
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> Now, file-mapped is maintaiend. But more generic update function
> will be needed for dirty page accounting.
> 
> For accountig page status, we have to guarantee lock_page_cgroup()
> will be never called under tree_lock held.
> To guarantee that, we use trylock at updating status.
> By this, we do fuzyy accounting, but in almost all case, it's correct.
> 
> Changelog:
>  - removed unnecessary preempt_disable()
>  - added root cgroup check. By this, we do no lock/account in root cgroup.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Looks good overall.


Thanks,
Daisuke Nishimura.

> ---
>  include/linux/memcontrol.h  |    7 ++-
>  include/linux/page_cgroup.h |   15 +++++++
>  mm/memcontrol.c             |   92 +++++++++++++++++++++++++++++++++-----------
>  mm/rmap.c                   |    4 -
>  4 files changed, 94 insertions(+), 24 deletions(-)
> 
> Index: mmotm-2.6.34-Mar9/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/mm/memcontrol.c
> +++ mmotm-2.6.34-Mar9/mm/memcontrol.c
> @@ -1348,30 +1348,83 @@ bool mem_cgroup_handle_oom(struct mem_cg
>   * Currently used to update mapped file statistics, but the routine can be
>   * generalized to update other statistics as well.
>   */
> -void mem_cgroup_update_file_mapped(struct page *page, int val)
> +void __mem_cgroup_update_stat(struct page_cgroup *pc, int idx, bool charge)
>  {
>  	struct mem_cgroup *mem;
> -	struct page_cgroup *pc;
> -
> -	pc = lookup_page_cgroup(page);
> -	if (unlikely(!pc))
> -		return;
> +	int val;
>  
> -	lock_page_cgroup(pc);
>  	mem = pc->mem_cgroup;
> -	if (!mem)
> -		goto done;
> +	if (!mem || !PageCgroupUsed(pc))
> +		return;
>  
> -	if (!PageCgroupUsed(pc))
> -		goto done;
> +	if (charge)
> +		val = 1;
> +	else
> +		val = -1;
>  
> +	switch (idx) {
> +	case MEMCG_NR_FILE_MAPPED:
> +		if (charge) {
> +			if (!PageCgroupFileMapped(pc))
> +				SetPageCgroupFileMapped(pc);
> +			else
> +				val = 0;
> +		} else {
> +			if (PageCgroupFileMapped(pc))
> +				ClearPageCgroupFileMapped(pc);
> +			else
> +				val = 0;
> +		}
> +		idx = MEM_CGROUP_STAT_FILE_MAPPED;
> +		break;
> +	default:
> +		BUG();
> +		break;
> +	}
>  	/*
>  	 * Preemption is already disabled. We can use __this_cpu_xxx
>  	 */
> -	__this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED], val);
> +	__this_cpu_add(mem->stat->count[idx], val);
> +}
>  
> -done:
> -	unlock_page_cgroup(pc);
> +void mem_cgroup_update_stat(struct page *page, int idx, bool charge)
> +{
> +	struct page_cgroup *pc;
> +
> +	pc = lookup_page_cgroup(page);
> +	if (!pc || mem_cgroup_is_root(pc->mem_cgroup))
> +		return;
> +
> +	if (trylock_page_cgroup(pc)) {
> +		__mem_cgroup_update_stat(pc, idx, charge);
> +		unlock_page_cgroup(pc);
> +	}
> +	return;
> +}
> +
> +static void mem_cgroup_migrate_stat(struct page_cgroup *pc,
> +	struct mem_cgroup *from, struct mem_cgroup *to)
> +{
> +	if (PageCgroupFileMapped(pc)) {
> +		__this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> +		if (!mem_cgroup_is_root(to)) {
> +			__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> +		} else {
> +			ClearPageCgroupFileMapped(pc);
> +		}
> +	}
> +}
> +
> +static void
> +__mem_cgroup_stat_fixup(struct page_cgroup *pc, struct mem_cgroup *mem)
> +{
> +	if (mem_cgroup_is_root(mem))
> +		return;
> +	/* We'are in uncharge() and lock_page_cgroup */
> +	if (PageCgroupFileMapped(pc)) {
> +		__this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> +		ClearPageCgroupFileMapped(pc);
> +	}
>  }
>  
>  /*
> @@ -1810,13 +1863,7 @@ static void __mem_cgroup_move_account(st
>  	VM_BUG_ON(pc->mem_cgroup != from);
>  
>  	page = pc->page;
> -	if (page_mapped(page) && !PageAnon(page)) {
> -		/* Update mapped_file data for mem_cgroup */
> -		preempt_disable();
> -		__this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> -		__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> -		preempt_enable();
> -	}
> +	mem_cgroup_migrate_stat(pc, from, to);
>  	mem_cgroup_charge_statistics(from, pc, false);
>  	if (uncharge)
>  		/* This is not "cancel", but cancel_charge does all we need. */
> @@ -2208,6 +2255,9 @@ __mem_cgroup_uncharge_common(struct page
>  		__do_uncharge(mem, ctype);
>  	if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
>  		mem_cgroup_swap_statistics(mem, true);
> +	if (unlikely(PCG_PageStatMask & pc->flags))
> +		__mem_cgroup_stat_fixup(pc, mem);
> +
>  	mem_cgroup_charge_statistics(mem, pc, false);
>  
>  	ClearPageCgroupUsed(pc);
> Index: mmotm-2.6.34-Mar9/include/linux/page_cgroup.h
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/include/linux/page_cgroup.h
> +++ mmotm-2.6.34-Mar9/include/linux/page_cgroup.h
> @@ -39,6 +39,8 @@ enum {
>  	PCG_CACHE, /* charged as cache */
>  	PCG_USED, /* this object is in use. */
>  	PCG_ACCT_LRU, /* page has been accounted for */
> +	/* for cache-status accounting */
> +	PCG_FILE_MAPPED,
>  };
>  
>  #define TESTPCGFLAG(uname, lname)			\
> @@ -57,6 +59,10 @@ static inline void ClearPageCgroup##unam
>  static inline int TestClearPageCgroup##uname(struct page_cgroup *pc)	\
>  	{ return test_and_clear_bit(PCG_##lname, &pc->flags);  }
>  
> +/* Page/File stat flag mask */
> +#define PCG_PageStatMask	((1 << PCG_FILE_MAPPED))
> +
> +
>  TESTPCGFLAG(Locked, LOCK)
>  
>  /* Cache flag is set only once (at allocation) */
> @@ -73,6 +79,10 @@ CLEARPCGFLAG(AcctLRU, ACCT_LRU)
>  TESTPCGFLAG(AcctLRU, ACCT_LRU)
>  TESTCLEARPCGFLAG(AcctLRU, ACCT_LRU)
>  
> +TESTPCGFLAG(FileMapped, FILE_MAPPED)
> +SETPCGFLAG(FileMapped, FILE_MAPPED)
> +CLEARPCGFLAG(FileMapped, FILE_MAPPED)
> +
>  static inline int page_cgroup_nid(struct page_cgroup *pc)
>  {
>  	return page_to_nid(pc->page);
> @@ -93,6 +103,11 @@ static inline void unlock_page_cgroup(st
>  	bit_spin_unlock(PCG_LOCK, &pc->flags);
>  }
>  
> +static inline int trylock_page_cgroup(struct page_cgroup *pc)
> +{
> +	return bit_spin_trylock(PCG_LOCK, &pc->flags);
> +}
> +
>  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
>  struct page_cgroup;
>  
> Index: mmotm-2.6.34-Mar9/include/linux/memcontrol.h
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/include/linux/memcontrol.h
> +++ mmotm-2.6.34-Mar9/include/linux/memcontrol.h
> @@ -124,7 +124,12 @@ static inline bool mem_cgroup_disabled(v
>  	return false;
>  }
>  
> -void mem_cgroup_update_file_mapped(struct page *page, int val);
> +enum mem_cgroup_page_stat_item {
> +	MEMCG_NR_FILE_MAPPED,
> +	MEMCG_NR_FILE_NSTAT,
> +};
> +
> +void mem_cgroup_update_stat(struct page *page, int idx, bool charge);
>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>  						gfp_t gfp_mask, int nid,
>  						int zid);
> Index: mmotm-2.6.34-Mar9/mm/rmap.c
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/mm/rmap.c
> +++ mmotm-2.6.34-Mar9/mm/rmap.c
> @@ -829,7 +829,7 @@ void page_add_file_rmap(struct page *pag
>  {
>  	if (atomic_inc_and_test(&page->_mapcount)) {
>  		__inc_zone_page_state(page, NR_FILE_MAPPED);
> -		mem_cgroup_update_file_mapped(page, 1);
> +		mem_cgroup_update_stat(page, MEMCG_NR_FILE_MAPPED, true);
>  	}
>  }
>  
> @@ -861,7 +861,7 @@ void page_remove_rmap(struct page *page)
>  		__dec_zone_page_state(page, NR_ANON_PAGES);
>  	} else {
>  		__dec_zone_page_state(page, NR_FILE_MAPPED);
> -		mem_cgroup_update_file_mapped(page, -1);
> +		mem_cgroup_update_stat(page, MEMCG_NR_FILE_MAPPED, false);
>  	}
>  	/*
>  	 * It would be tidy to reset the PageAnon mapping here,
> 

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