Re: [PATCH -V7 07/14] mm/page_cgroup: Make page_cgroup point to thecgroup rather than the mem_cgroup

[Kamezawa Hiroyuki]

(2012/05/30 23:38), Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V"<aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> 
> We will use it later to make page_cgroup track the hugetlb cgroup information.
> 
> Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
>   include/linux/mmzone.h      |    2 +-
>   include/linux/page_cgroup.h |    8 ++++----
>   init/Kconfig                |    4 ++++
>   mm/Makefile                 |    3 ++-
>   mm/memcontrol.c             |   42 +++++++++++++++++++++++++-----------------
>   5 files changed, 36 insertions(+), 23 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2427706..2483cc5 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1052,7 +1052,7 @@ struct mem_section {
> 
>   	/* See declaration of similar field in struct zone */
>   	unsigned long *pageblock_flags;
> -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +#ifdef CONFIG_PAGE_CGROUP
>   	/*
>   	 * If !SPARSEMEM, pgdat doesn't have page_cgroup pointer. We use
>   	 * section. (see memcontrol.h/page_cgroup.h about this.)
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index a88cdba..7bbfe37 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -12,7 +12,7 @@ enum {
>   #ifndef __GENERATING_BOUNDS_H
>   #include<generated/bounds.h>
> 
> -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +#ifdef CONFIG_PAGE_CGROUP
>   #include<linux/bit_spinlock.h>
> 
>   /*
> @@ -24,7 +24,7 @@ enum {
>    */
>   struct page_cgroup {
>   	unsigned long flags;
> -	struct mem_cgroup *mem_cgroup;
> +	struct cgroup *cgroup;
>   };
> 

This patch seems very bad.

  - What is the performance impact to memcg ? Doesn't this add extra overheads 
    to memcg lookup ?
  - Hugetlb reuquires much more smaller number of tracking information rather
    than memcg requires. I guess you can record the information into page->private
    if you want.
  - This may prevent us from the work 'reducing size of page_cgroup'

So, strong Nack to this. I guess you can use page->private or some entries in
struct page, you have many pages per accounting units. Please make an effort
to avoid using page_cgroup.

Thanks,
-Kame



>   void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat);
> @@ -82,7 +82,7 @@ static inline void unlock_page_cgroup(struct page_cgroup *pc)
>   	bit_spin_unlock(PCG_LOCK,&pc->flags);
>   }
> 
> -#else /* CONFIG_CGROUP_MEM_RES_CTLR */
> +#else /* CONFIG_PAGE_CGROUP */
>   struct page_cgroup;
> 
>   static inline void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat)
> @@ -102,7 +102,7 @@ static inline void __init page_cgroup_init_flatmem(void)
>   {
>   }
> 
> -#endif /* CONFIG_CGROUP_MEM_RES_CTLR */
> +#endif /* CONFIG_PAGE_CGROUP */
> 
>   #include<linux/swap.h>
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 81816b8..1363203 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -687,10 +687,14 @@ config RESOURCE_COUNTERS
>   	  This option enables controller independent resource accounting
>   	  infrastructure that works with cgroups.
> 
> +config PAGE_CGROUP
> +       bool
> +
>   config CGROUP_MEM_RES_CTLR
>   	bool "Memory Resource Controller for Control Groups"
>   	depends on RESOURCE_COUNTERS
>   	select MM_OWNER
> +	select PAGE_CGROUP
>   	help
>   	  Provides a memory resource controller that manages both anonymous
>   	  memory and page cache. (See Documentation/cgroups/memory.txt)
> diff --git a/mm/Makefile b/mm/Makefile
> index a156285..a70f9a9 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -47,7 +47,8 @@ obj-$(CONFIG_FS_XIP) += filemap_xip.o
>   obj-$(CONFIG_MIGRATION) += migrate.o
>   obj-$(CONFIG_QUICKLIST) += quicklist.o
>   obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o
> -obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o page_cgroup.o
> +obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
> +obj-$(CONFIG_PAGE_CGROUP) += page_cgroup.o
>   obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
>   obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
>   obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ac35bcc..6df019b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -864,6 +864,8 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
> 
>   struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
>   {
> +	if (!cont)
> +		return NULL;
>   	return container_of(cgroup_subsys_state(cont,
>   				mem_cgroup_subsys_id), struct mem_cgroup,
>   				css);
> @@ -1097,7 +1099,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
>   		return&zone->lruvec;
> 
>   	pc = lookup_page_cgroup(page);
> -	memcg = pc->mem_cgroup;
> +	memcg = mem_cgroup_from_cont(pc->cgroup);
> 
>   	/*
>   	 * Surreptitiously switch any uncharged offlist page to root:
> @@ -1108,8 +1110,10 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
>   	 * under page_cgroup lock: between them, they make all uses
>   	 * of pc->mem_cgroup safe.
>   	 */
> -	if (!PageLRU(page)&&  !PageCgroupUsed(pc)&&  memcg != root_mem_cgroup)
> -		pc->mem_cgroup = memcg = root_mem_cgroup;
> +	if (!PageLRU(page)&&  !PageCgroupUsed(pc)&&  memcg != root_mem_cgroup) {
> +		memcg = root_mem_cgroup;
> +		pc->cgroup = memcg->css.cgroup;
> +	}
> 
>   	mz = page_cgroup_zoneinfo(memcg, page);
>   	return&mz->lruvec;
> @@ -1889,12 +1893,14 @@ static bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask,
>   void __mem_cgroup_begin_update_page_stat(struct page *page,
>   				bool *locked, unsigned long *flags)
>   {
> +	struct cgroup *cgroup;
>   	struct mem_cgroup *memcg;
>   	struct page_cgroup *pc;
> 
>   	pc = lookup_page_cgroup(page);
>   again:
> -	memcg = pc->mem_cgroup;
> +	cgroup = pc->cgroup;
> +	memcg = mem_cgroup_from_cont(cgroup);
>   	if (unlikely(!memcg || !PageCgroupUsed(pc)))
>   		return;
>   	/*
> @@ -1907,7 +1913,7 @@ again:
>   		return;
> 
>   	move_lock_mem_cgroup(memcg, flags);
> -	if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
> +	if (cgroup != pc->cgroup || !PageCgroupUsed(pc)) {
>   		move_unlock_mem_cgroup(memcg, flags);
>   		goto again;
>   	}
> @@ -1923,7 +1929,7 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
>   	 * lock is held because a routine modifies pc->mem_cgroup
>   	 * should take move_lock_page_cgroup().
>   	 */
> -	move_unlock_mem_cgroup(pc->mem_cgroup, flags);
> +	move_unlock_mem_cgroup(mem_cgroup_from_cont(pc->cgroup), flags);
>   }
> 
>   void mem_cgroup_update_page_stat(struct page *page,
> @@ -1936,7 +1942,7 @@ void mem_cgroup_update_page_stat(struct page *page,
>   	if (mem_cgroup_disabled())
>   		return;
> 
> -	memcg = pc->mem_cgroup;
> +	memcg = mem_cgroup_from_cont(pc->cgroup);
>   	if (unlikely(!memcg || !PageCgroupUsed(pc)))
>   		return;
> 
> @@ -2444,7 +2450,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
>   	pc = lookup_page_cgroup(page);
>   	lock_page_cgroup(pc);
>   	if (PageCgroupUsed(pc)) {
> -		memcg = pc->mem_cgroup;
> +		memcg = mem_cgroup_from_cont(pc->cgroup);
>   		if (memcg&&  !css_tryget(&memcg->css))
>   			memcg = NULL;
>   	} else if (PageSwapCache(page)) {
> @@ -2491,14 +2497,15 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
>   		zone = page_zone(page);
>   		spin_lock_irq(&zone->lru_lock);
>   		if (PageLRU(page)) {
> -			lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
> +			lruvec = mem_cgroup_zone_lruvec(zone,
> +					mem_cgroup_from_cont(pc->cgroup));
>   			ClearPageLRU(page);
>   			del_page_from_lru_list(page, lruvec, page_lru(page));
>   			was_on_lru = true;
>   		}
>   	}
> 
> -	pc->mem_cgroup = memcg;
> +	pc->cgroup = memcg->css.cgroup;
>   	/*
>   	 * We access a page_cgroup asynchronously without lock_page_cgroup().
>   	 * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
> @@ -2511,7 +2518,8 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
> 
>   	if (lrucare) {
>   		if (was_on_lru) {
> -			lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
> +			lruvec = mem_cgroup_zone_lruvec(zone,
> +					mem_cgroup_from_cont(pc->cgroup));
>   			VM_BUG_ON(PageLRU(page));
>   			SetPageLRU(page);
>   			add_page_to_lru_list(page, lruvec, page_lru(page));
> @@ -2601,7 +2609,7 @@ static int mem_cgroup_move_account(struct page *page,
>   	lock_page_cgroup(pc);
> 
>   	ret = -EINVAL;
> -	if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
> +	if (!PageCgroupUsed(pc) || pc->cgroup != from->css.cgroup)
>   		goto unlock;
> 
>   	move_lock_mem_cgroup(from,&flags);
> @@ -2616,7 +2624,7 @@ static int mem_cgroup_move_account(struct page *page,
>   	mem_cgroup_charge_statistics(from, anon, -nr_pages);
> 
>   	/* caller should have done css_get */
> -	pc->mem_cgroup = to;
> +	pc->cgroup = to->css.cgroup;
>   	mem_cgroup_charge_statistics(to, anon, nr_pages);
>   	/*
>   	 * We charges against "to" which may not have any tasks. Then, "to"
> @@ -2937,7 +2945,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> 
>   	lock_page_cgroup(pc);
> 
> -	memcg = pc->mem_cgroup;
> +	memcg = mem_cgroup_from_cont(pc->cgroup);
> 
>   	if (!PageCgroupUsed(pc))
>   		goto unlock_out;
> @@ -3183,7 +3191,7 @@ int mem_cgroup_prepare_migration(struct page *page,
>   	pc = lookup_page_cgroup(page);
>   	lock_page_cgroup(pc);
>   	if (PageCgroupUsed(pc)) {
> -		memcg = pc->mem_cgroup;
> +		memcg = mem_cgroup_from_cont(pc->cgroup);
>   		css_get(&memcg->css);
>   		/*
>   		 * At migrating an anonymous page, its mapcount goes down
> @@ -3328,7 +3336,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
>   	/* fix accounting on old pages */
>   	lock_page_cgroup(pc);
>   	if (PageCgroupUsed(pc)) {
> -		memcg = pc->mem_cgroup;
> +		memcg = mem_cgroup_from_cont(pc->cgroup);
>   		mem_cgroup_charge_statistics(memcg, false, -1);
>   		ClearPageCgroupUsed(pc);
>   	}
> @@ -5135,7 +5143,7 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
>   		 * mem_cgroup_move_account() checks the pc is valid or not under
>   		 * the lock.
>   		 */
> -		if (PageCgroupUsed(pc)&&  pc->mem_cgroup == mc.from) {
> +		if (PageCgroupUsed(pc)&&  pc->cgroup == mc.from->css.cgroup) {
>   			ret = MC_TARGET_PAGE;
>   			if (target)
>   				target->page = page;


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