Re: [PATCH 2/5] use ID in page cgroup

[Greg Thelen]

KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Now, addresses of memory cgroup can be calculated by their ID without complex.
> This patch relplaces pc->mem_cgroup from a pointer to a unsigned short.
> On 64bit architecture, this offers us more 6bytes room per page_cgroup.
> Use 2bytes for blkio-cgroup's page tracking. More 4bytes will be used for
> some light-weight concurrent access.
>
> We may able to move this id onto flags field but ...go step by step.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
>  include/linux/page_cgroup.h |    3 ++-
>  mm/memcontrol.c             |   40 +++++++++++++++++++++++++---------------
>  mm/page_cgroup.c            |    2 +-
>  3 files changed, 28 insertions(+), 17 deletions(-)
>
> Index: mmotm-0727/include/linux/page_cgroup.h
> ===================================================================
> --- mmotm-0727.orig/include/linux/page_cgroup.h
> +++ mmotm-0727/include/linux/page_cgroup.h
> @@ -12,7 +12,8 @@
>   */
>  struct page_cgroup {
>  	unsigned long flags;
> -	struct mem_cgroup *mem_cgroup;
> +	unsigned short mem_cgroup;	/* ID of assigned memory cgroup */
> +	unsigned short blk_cgroup;	/* Not Used..but will be. */
>  	struct page *page;
>  	struct list_head lru;		/* per cgroup LRU list */
>  };
> Index: mmotm-0727/mm/page_cgroup.c
> ===================================================================
> --- mmotm-0727.orig/mm/page_cgroup.c
> +++ mmotm-0727/mm/page_cgroup.c
> @@ -15,7 +15,7 @@ static void __meminit
>  __init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
>  {
>  	pc->flags = 0;
> -	pc->mem_cgroup = NULL;
> +	pc->mem_cgroup = 0;
>  	pc->page = pfn_to_page(pfn);
>  	INIT_LIST_HEAD(&pc->lru);
>  }
> Index: mmotm-0727/mm/memcontrol.c
> ===================================================================
> --- mmotm-0727.orig/mm/memcontrol.c
> +++ mmotm-0727/mm/memcontrol.c
> @@ -376,7 +376,7 @@ struct cgroup_subsys_state *mem_cgroup_c
>  static struct mem_cgroup_per_zone *
>  page_cgroup_zoneinfo(struct page_cgroup *pc)
>  {
> -	struct mem_cgroup *mem = pc->mem_cgroup;
> +	struct mem_cgroup *mem = id_to_memcg(pc->mem_cgroup);
>  	int nid = page_cgroup_nid(pc);
>  	int zid = page_cgroup_zid(pc);
>  
> @@ -581,7 +581,11 @@ static void mem_cgroup_charge_statistics
>  					 bool charge)
>  {
>  	int val = (charge) ? 1 : -1;
> -
> +	if (pc->mem_cgroup == 0) {
> +		show_stack(NULL, NULL);
> +		printk("charge to 0\n");
> +		while(1);
> +	}
Why hang the task here.  If this is bad then maybe BUG_ON()?
>  	preempt_disable();
>  
>  	if (PageCgroupCache(pc))
> @@ -718,6 +722,11 @@ static inline bool mem_cgroup_is_root(st
>  	return (mem == root_mem_cgroup);
>  }
>  
> +static inline bool mem_cgroup_is_rootid(unsigned short id)
> +{
> +	return (id == 1);
> +}
> +
>  /*
>   * Following LRU functions are allowed to be used without PCG_LOCK.
>   * Operations are called by routine of global LRU independently from memcg.
> @@ -750,7 +759,7 @@ void mem_cgroup_del_lru_list(struct page
>  	 */
>  	mz = page_cgroup_zoneinfo(pc);
>  	MEM_CGROUP_ZSTAT(mz, lru) -= 1;
> -	if (mem_cgroup_is_root(pc->mem_cgroup))
> +	if (mem_cgroup_is_rootid(pc->mem_cgroup))
>  		return;
>  	VM_BUG_ON(list_empty(&pc->lru));
>  	list_del_init(&pc->lru);
> @@ -777,7 +786,7 @@ void mem_cgroup_rotate_lru_list(struct p
>  	 */
>  	smp_rmb();
>  	/* unused or root page is not rotated. */
> -	if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
> +	if (!PageCgroupUsed(pc) || mem_cgroup_is_rootid(pc->mem_cgroup))
>  		return;
>  	mz = page_cgroup_zoneinfo(pc);
>  	list_move(&pc->lru, &mz->lists[lru]);
> @@ -803,7 +812,7 @@ void mem_cgroup_add_lru_list(struct page
>  	mz = page_cgroup_zoneinfo(pc);
>  	MEM_CGROUP_ZSTAT(mz, lru) += 1;
>  	SetPageCgroupAcctLRU(pc);
> -	if (mem_cgroup_is_root(pc->mem_cgroup))
> +	if (mem_cgroup_is_rootid(pc->mem_cgroup))
>  		return;
>  	list_add(&pc->lru, &mz->lists[lru]);
>  }
> @@ -1471,7 +1480,7 @@ void mem_cgroup_update_file_mapped(struc
>  		return;
>  
>  	lock_page_cgroup(pc);
> -	mem = pc->mem_cgroup;
> +	mem = id_to_memcg(pc->mem_cgroup);
>  	if (!mem || !PageCgroupUsed(pc))
>  		goto done;
>  
> @@ -1859,7 +1868,7 @@ struct mem_cgroup *try_get_mem_cgroup_fr
>  	pc = lookup_page_cgroup(page);
>  	lock_page_cgroup(pc);
>  	if (PageCgroupUsed(pc)) {
> -		mem = pc->mem_cgroup;
> +		mem = id_to_memcg(pc->mem_cgroup);
>  		if (mem && !css_tryget(&mem->css))
>  			mem = NULL;
>  	} else if (PageSwapCache(page)) {
> @@ -1895,7 +1904,7 @@ static void __mem_cgroup_commit_charge(s
>  		return;
>  	}
>  
> -	pc->mem_cgroup = mem;
> +	pc->mem_cgroup = css_id(&mem->css);
>  	/*
>  	 * We access a page_cgroup asynchronously without lock_page_cgroup().
>  	 * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
> @@ -1953,7 +1962,7 @@ static void __mem_cgroup_move_account(st
>  	VM_BUG_ON(PageLRU(pc->page));
>  	VM_BUG_ON(!PageCgroupLocked(pc));
>  	VM_BUG_ON(!PageCgroupUsed(pc));
> -	VM_BUG_ON(pc->mem_cgroup != from);
> +	VM_BUG_ON(id_to_memcg(pc->mem_cgroup) != from);
>  
>  	if (PageCgroupFileMapped(pc)) {
>  		/* Update mapped_file data for mem_cgroup */
> @@ -1968,7 +1977,7 @@ static void __mem_cgroup_move_account(st
>  		mem_cgroup_cancel_charge(from);
>  
>  	/* caller should have done css_get */
> -	pc->mem_cgroup = to;
> +	pc->mem_cgroup = css_id(&to->css);
>  	mem_cgroup_charge_statistics(to, pc, true);
>  	/*
>  	 * We charges against "to" which may not have any tasks. Then, "to"
> @@ -1988,7 +1997,7 @@ static int mem_cgroup_move_account(struc
>  {
>  	int ret = -EINVAL;
>  	lock_page_cgroup(pc);
> -	if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
> +	if (PageCgroupUsed(pc) && id_to_memcg(pc->mem_cgroup) == from) {
>  		__mem_cgroup_move_account(pc, from, to, uncharge);
>  		ret = 0;
>  	}
> @@ -2327,9 +2336,9 @@ __mem_cgroup_uncharge_common(struct page
>  
>  	lock_page_cgroup(pc);
>  
> -	mem = pc->mem_cgroup;
> +	mem = id_to_memcg(pc->mem_cgroup);
>  
> -	if (!PageCgroupUsed(pc))
> +	if (!mem || !PageCgroupUsed(pc))
Why add the extra !mem check here?

Can PageCgroupUsed() return true if mem==NULL?

>  		goto unlock_out;
>  
>  	switch (ctype) {
> @@ -2572,7 +2581,7 @@ int mem_cgroup_prepare_migration(struct 
>  	pc = lookup_page_cgroup(page);
>  	lock_page_cgroup(pc);
>  	if (PageCgroupUsed(pc)) {
> -		mem = pc->mem_cgroup;
> +		mem = id_to_memcg(pc->mem_cgroup);
>  		css_get(&mem->css);
>  		/*
>  		 * At migrating an anonymous page, its mapcount goes down
> @@ -4396,7 +4405,8 @@ static int is_target_pte_for_mc(struct v
>  		 * 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) &&
> +			id_to_memcg(pc->mem_cgroup) == mc.from) {
>  			ret = MC_TARGET_PAGE;
>  			if (target)
>  				target->page = page;
--
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