Re: [RFC] Low overhead patches for the memory resource controller

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

On Wed, 13 May 2009 21:02:18 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Important: Not for inclusion, for discussion only
> 
> I've been experimenting with a version of the patches below. They add
> a PCGF_ROOT flag for tracking pages belonging to the root cgroup and
> disable LRU manipulation for them
> 
> Caveats:
> 
> 1. I've not checked accounting, accounting might be broken
> 2. I've not made the root cgroup as non limitable, we need to disable
> hard limits once we agree to go with this
> 
> 
> Tests
> 
> Quick tests show an improvement with AIM9
> 
>                 mmotm+patch     mmtom-08-may-2009
> AIM9            1338.57         1338.17
> Dbase           18034.16        16021.58
> New Dbase       18482.24        16518.54
> Shared          9935.98         8882.11
> Compute         16619.81        15226.13
> 
> Comments on the approach much appreciated
> 
> Feature: Remove the overhead associated with the root cgroup
> 
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
> 
> This patch changes the memory cgroup and removes the overhead associated
> with accounting all pages in the root cgroup. As a side-effect, we can
> no longer set a memory hard limit in the root cgroup.
> 
> A new flag is used to track page_cgroup associated with the root cgroup
> pages.
> ---
> 
>  include/linux/page_cgroup.h |    5 +++++
>  mm/memcontrol.c             |   23 +++++++++++++++++------
>  mm/page_cgroup.c            |    1 -
>  3 files changed, 22 insertions(+), 7 deletions(-)
> 
> 
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 7339c7b..9c88e85 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_ROOT, /* page belongs to root cgroup */
>  };
>  
>  #define TESTPCGFLAG(uname, lname)			\
> @@ -46,6 +47,10 @@ TESTPCGFLAG(Cache, CACHE)
>  TESTPCGFLAG(Used, USED)
>  CLEARPCGFLAG(Used, USED)
>  
> +SETPCGFLAG(Root, ROOT)
> +CLEARPCGFLAG(Root, ROOT)
> +TESTPCGFLAG(Root, ROOT)
> +
>  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 9712ef7..2750bed 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -43,6 +43,7 @@
>  
>  struct cgroup_subsys mem_cgroup_subsys __read_mostly;
>  #define MEM_CGROUP_RECLAIM_RETRIES	5
> +struct mem_cgroup *root_mem_cgroup __read_mostly;
>  
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
>  /* Turned on only when memory cgroup is enabled && really_do_swap_account = 0 */
> @@ -196,6 +197,7 @@ enum charge_type {
>  #define PCGF_CACHE	(1UL << PCG_CACHE)
>  #define PCGF_USED	(1UL << PCG_USED)
>  #define PCGF_LOCK	(1UL << PCG_LOCK)
> +#define PCGF_ROOT	(1UL << PCG_ROOT)
>  static const unsigned long
>  pcg_default_flags[NR_CHARGE_TYPE] = {
>  	PCGF_CACHE | PCGF_USED | PCGF_LOCK, /* File Cache */
> @@ -422,6 +424,8 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
>  	/* can happen while we handle swapcache. */
>  	if (list_empty(&pc->lru) || !pc->mem_cgroup)
>  		return;
> +	if (PageCgroupRoot(pc))
> +		return;
>  	/*
>  	 * We don't check PCG_USED bit. It's cleared when the "page" is finally
>  	 * removed from global LRU.
> @@ -452,8 +456,8 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
>  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
>  	 */
>  	smp_rmb();
> -	/* unused page is not rotated. */
> -	if (!PageCgroupUsed(pc))
> +	/* unused or root page is not rotated. */
> +	if (!PageCgroupUsed(pc) || PageCgroupRoot(pc))
>  		return;
>  	mz = page_cgroup_zoneinfo(pc);
>  	list_move(&pc->lru, &mz->lists[lru]);
> @@ -472,7 +476,7 @@ 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))
> +	if (!PageCgroupUsed(pc) || PageCgroupRoot(pc))
>  		return;
>  
>  	mz = page_cgroup_zoneinfo(pc);
> @@ -1114,9 +1118,12 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>  		css_put(&mem->css);
>  		return;
>  	}
> -	pc->mem_cgroup = mem;
> -	smp_wmb();
> -	pc->flags = pcg_default_flags[ctype];
> +	if (mem != root_mem_cgroup) {
> +		pc->mem_cgroup = mem;
> +		smp_wmb();
> +		pc->flags = pcg_default_flags[ctype];
> +	} else
> +		SetPageCgroupRoot(pc);
>  
This means
  PCG_USED is not set. (then uncharge_common will be skipped completely.)
  LOCK bit is dropped here.

After fix, the test result will change.

Thanks,
-Kame



>  	mem_cgroup_charge_statistics(mem, pc, true);
>  
> @@ -1521,6 +1528,8 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
>  	mem_cgroup_charge_statistics(mem, pc, false);
>  
>  	ClearPageCgroupUsed(pc);
> +	if (mem == root_mem_cgroup)
> +		ClearPageCgroupRoot(pc);
>  	/*
>  	 * pc->mem_cgroup is not cleared here. It will be accessed when it's
>  	 * freed from LRU. This is safe because uncharged page is expected not
> @@ -2504,6 +2513,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	if (cont->parent == NULL) {
>  		enable_swap_cgroup();
>  		parent = NULL;
> +		root_mem_cgroup = mem;
>  	} else {
>  		parent = mem_cgroup_from_cont(cont->parent);
>  		mem->use_hierarchy = parent->use_hierarchy;
> @@ -2532,6 +2542,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	return &mem->css;
>  free_out:
>  	__mem_cgroup_free(mem);
> +	root_mem_cgroup = NULL;
>  	return ERR_PTR(error);
>  }
>  
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index 09b73c5..6145ff6 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -276,7 +276,6 @@ void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat)
>  
>  #endif
>  
> -
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
>  
>  static DEFINE_MUTEX(swap_cgroup_mutex);
> 
> -- 
>         Thanks!
> 	Balbir
> 

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