memcontrol.c

done:
	*memcg = mem;
	return 0;
nomem:
	*memcg = NULL;
	return -ENOMEM;
bypass:
	*memcg = NULL;
	return 0;
}

/*
 * Somemtimes we have to undo a charge we got by try_charge().
 * This function is for that and do uncharge, put css's refcnt.
 * gotten by try_charge().
 */
static void __mem_cgroup_cancel_charge(struct mem_cgroup *mem,
							unsigned long count)
{
	if (!mem_cgroup_is_root(mem)) {
		res_counter_uncharge(&mem->res, PAGE_SIZE * count);
		if (do_swap_account)
			res_counter_uncharge(&mem->memsw, PAGE_SIZE * count);
	}
}

static void mem_cgroup_cancel_charge(struct mem_cgroup *mem,
				     int page_size)
{
	__mem_cgroup_cancel_charge(mem, page_size >> PAGE_SHIFT);
}

/*
 * A helper function to get mem_cgroup from ID. must be called under
 * rcu_read_lock(). The caller must check css_is_removed() or some if
 * it's concern. (dropping refcnt from swap can be called against removed
 * memcg.)
 */
static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
{
	struct cgroup_subsys_state *css;

	/* ID 0 is unused ID */
	if (!id)
		return NULL;
	css = css_lookup(&mem_cgroup_subsys, id);
	if (!css)
		return NULL;
	return container_of(css, struct mem_cgroup, css);
}

struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
	struct mem_cgroup *mem = NULL;
	struct page_cgroup *pc;
	unsigned short id;
	swp_entry_t ent;

	VM_BUG_ON(!PageLocked(page));

	pc = lookup_page_cgroup(page);
	lock_page_cgroup(pc);
	if (PageCgroupUsed(pc)) {
		mem = pc->mem_cgroup;
		if (mem && !css_tryget(&mem->css))
			mem = NULL;
	} else if (PageSwapCache(page)) {
		ent.val = page_private(page);
		id = lookup_swap_cgroup(ent);
		rcu_read_lock();
		mem = mem_cgroup_lookup(id);
		if (mem && !css_tryget(&mem->css))
			mem = NULL;
		rcu_read_unlock();
	}
	unlock_page_cgroup(pc);
	return mem;
}

static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
				       struct page_cgroup *pc,
				       enum charge_type ctype,
				       int page_size)
{
	int nr_pages = page_size >> PAGE_SHIFT;

	/* try_charge() can return NULL to *memcg, taking care of it. */
	if (!mem)
		return;

	lock_page_cgroup(pc);
	if (unlikely(PageCgroupUsed(pc))) {
		unlock_page_cgroup(pc);
		mem_cgroup_cancel_charge(mem, page_size);
		return;
	}
	/*
	 * we don't need page_cgroup_lock about tail pages, becase they are not
	 * accessed by any other context at this point.
	 */
	pc->mem_cgroup = mem;
	/*
	 * We access a page_cgroup asynchronously without lock_page_cgroup().
	 * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
	 * is accessed after testing USED bit. To make pc->mem_cgroup visible
	 * before USED bit, we need memory barrier here.
	 * See mem_cgroup_add_lru_list(), etc.
 	 */
	smp_wmb();
	switch (ctype) {
	case MEM_CGROUP_CHARGE_TYPE_CACHE:
	case MEM_CGROUP_CHARGE_TYPE_SHMEM:
		SetPageCgroupCache(pc);
		SetPageCgroupUsed(pc);
		break;
	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
		ClearPageCgroupCache(pc);
		SetPageCgroupUsed(pc);
		break;
	default:
		break;
	}

	mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), nr_pages);
	unlock_page_cgroup(pc);
	/*
	 * "charge_statistics" updated event counter. Then, check it.
	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
	 * if they exceeds softlimit.
	 */
	memcg_check_events(mem, pc->page);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (1 << PCG_MOVE_LOCK) |\
			(1 << PCG_ACCT_LRU) | (1 << PCG_MIGRATION))
/*
 * Because tail pages are not marked as "used", set it. We're under
 * zone->lru_lock, 'splitting on pmd' and compund_lock.
 */
void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)
{
	struct page_cgroup *head_pc = lookup_page_cgroup(head);
	struct page_cgroup *tail_pc = lookup_page_cgroup(tail);
	unsigned long flags;

	if (mem_cgroup_disabled())
		return;
	/*
	 * We have no races with charge/uncharge but will have races with
	 * page state accounting.
	 */
	move_lock_page_cgroup(head_pc, &flags);

	tail_pc->mem_cgroup = head_pc->mem_cgroup;
	smp_wmb(); /* see __commit_charge() */
	if (PageCgroupAcctLRU(head_pc)) {
		enum lru_list lru;
		struct mem_cgroup_per_zone *mz;

		/*
		 * LRU flags cannot be copied because we need to add tail
		 *.page to LRU by generic call and our hook will be called.
		 * We hold lru_lock, then, reduce counter directly.
		 */
		lru = page_lru(head);
		mz = page_cgroup_zoneinfo(head_pc);
		MEM_CGROUP_ZSTAT(mz, lru) -= 1;
	}
	tail_pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
	move_unlock_page_cgroup(head_pc, &flags);
}
#endif

/**
 * __mem_cgroup_move_account - move account of the page
 * @pc:	page_cgroup of the page.
 * @from: mem_cgroup which the page is moved from.
 * @to:	mem_cgroup which the page is moved to. @from != @to.
 * @uncharge: whether we should call uncharge and css_put against @from.
 *
 * The caller must confirm following.
 * - page is not on LRU (isolate_page() is useful.)
 * - the pc is locked, used, and ->mem_cgroup points to @from.
 *
 * This function doesn't do "charge" nor css_get to new cgroup. It should be
 * done by a caller(__mem_cgroup_try_charge would be usefull). If @uncharge is
 * true, this function does "uncharge" from old cgroup, but it doesn't if
 * @uncharge is false, so a caller should do "uncharge".
 */

static void __mem_cgroup_move_account(struct page_cgroup *pc,
	struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge,
	int charge_size)
{
	int nr_pages = charge_size >> PAGE_SHIFT;

	VM_BUG_ON(from == to);
	VM_BUG_ON(PageLRU(pc->page));
	VM_BUG_ON(!page_is_cgroup_locked(pc));
	VM_BUG_ON(!PageCgroupUsed(pc));
	VM_BUG_ON(pc->mem_cgroup != from);

	if (PageCgroupFileMapped(pc)) {
		/* 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_charge_statistics(from, PageCgroupCache(pc), -nr_pages);
	if (uncharge)
		/* This is not "cancel", but cancel_charge does all we need. */
		mem_cgroup_cancel_charge(from, charge_size);

	/* caller should have done css_get */
	pc->mem_cgroup = to;
	mem_cgroup_charge_statistics(to, PageCgroupCache(pc), nr_pages);
	/*
	 * We charges against "to" which may not have any tasks. Then, "to"
	 * can be under rmdir(). But in current implementation, caller of
	 * this function is just force_empty() and move charge, so it's
	 * garanteed that "to" is never removed. So, we don't check rmdir
	 * status here.
	 */
}

/*
 * check whether the @pc is valid for moving account and call
 * __mem_cgroup_move_account()
 */
static int mem_cgroup_move_account(struct page_cgroup *pc,
		struct mem_cgroup *from, struct mem_cgroup *to,
		bool uncharge, int charge_size)
{
	int ret = -EINVAL;
	unsigned long flags;

	if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page))
		return -EBUSY;

	lock_page_cgroup(pc);
	if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
		move_lock_page_cgroup(pc, &flags);
		__mem_cgroup_move_account(pc, from, to, uncharge, charge_size);
		move_unlock_page_cgroup(pc, &flags);
		ret = 0;
	}
	unlock_page_cgroup(pc);
	/*
	 * check events
	 */
	memcg_check_events(to, pc->page);
	memcg_check_events(from, pc->page);
	return ret;
}

/*
 * move charges to its parent.
 */

static int mem_cgroup_move_parent(struct page_cgroup *pc,
				  struct mem_cgroup *child,
				  gfp_t gfp_mask)
{
	struct page *page = pc->page;
	struct cgroup *cg = child->css.cgroup;
	struct cgroup *pcg = cg->parent;
	struct mem_cgroup *parent;
	int charge = PAGE_SIZE;
	unsigned long flags;
	int ret;

	/* Is ROOT ? */
	if (!pcg)
		return -EINVAL;

	ret = -EBUSY;
	if (!get_page_unless_zero(page))
		goto out;
	if (isolate_lru_page(page))
		goto put;
	/* The page is isolated from LRU and we have no race with splitting */
	charge = PAGE_SIZE << compound_order(page);

	parent = mem_cgroup_from_cont(pcg);
	ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge);
	if (ret || !parent)
		goto put_back;

	if (charge > PAGE_SIZE)
		flags = compound_lock_irqsave(page);

	ret = mem_cgroup_move_account(pc, child, parent, true, charge);
	if (ret)
		mem_cgroup_cancel_charge(parent, charge);

	if (charge > PAGE_SIZE)
		compound_unlock_irqrestore(page, flags);
put_back:
	putback_lru_page(page);
put:
	put_page(page);
out:
	return ret;
}

/*
 * 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 *mem = NULL;
	struct page_cgroup *pc;
	int ret;
	int page_size = PAGE_SIZE;

	if (PageTransHuge(page)) {
		page_size <<= compound_order(page);
		VM_BUG_ON(!PageTransHuge(page));
	}

	pc = lookup_page_cgroup(page);
	/* can happen at boot */
	if (unlikely(!pc))
		return 0;
	prefetchw(pc);

	ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, true, page_size);
	if (ret || !mem)
		return ret;

	__mem_cgroup_commit_charge(mem, pc, ctype, page_size);
	return 0;
}

int mem_cgroup_newpage_charge(struct page *page,
			      struct mm_struct *mm, gfp_t gfp_mask)
{
	if (mem_cgroup_disabled())
		return 0;
	/*
	 * If already mapped, we don't have to account.
	 * If page cache, page->mapping has address_space.
	 * But page->mapping may have out-of-use anon_vma pointer,
	 * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
	 * is NULL.
  	 */
	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);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
					enum charge_type ctype);

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
				gfp_t gfp_mask)
{
	int ret;

	if (mem_cgroup_disabled())
		return 0;
	if (PageCompound(page))
		return 0;
	/*
	 * Corner case handling. This is called from add_to_page_cache()
	 * in usual. But some FS (shmem) precharges this page before calling it
	 * and call add_to_page_cache() with GFP_NOWAIT.
	 *
	 * For GFP_NOWAIT case, the page may be pre-charged before calling
	 * add_to_page_cache(). (See shmem.c) check it here and avoid to call
	 * charge twice. (It works but has to pay a bit larger cost.)
	 * And when the page is SwapCache, it should take swap information
	 * into account. This is under lock_page() now.
	 */
	if (!(gfp_mask & __GFP_WAIT)) {
		struct page_cgroup *pc;

		pc = lookup_page_cgroup(page);
		if (!pc)
			return 0;
		lock_page_cgroup(pc);
		if (PageCgroupUsed(pc)) {
			unlock_page_cgroup(pc);
			return 0;
		}
		unlock_page_cgroup(pc);
	}

	if (unlikely(!mm))
		mm = &init_mm;

	if (page_is_file_cache(page))
		return mem_cgroup_charge_common(page, mm, gfp_mask,
				MEM_CGROUP_CHARGE_TYPE_CACHE);

	/* shmem */
	if (PageSwapCache(page)) {
		struct mem_cgroup *mem = NULL;

		ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
		if (!ret)
			__mem_cgroup_commit_charge_swapin(page, mem,
					MEM_CGROUP_CHARGE_TYPE_SHMEM);
	} else
		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
					MEM_CGROUP_CHARGE_TYPE_SHMEM);

	return ret;
}

/*
 * While swap-in, try_charge -> commit or cancel, the page is locked.
 * And when try_charge() successfully returns, one refcnt to memcg without
 * struct page_cgroup is acquired. This refcnt will be consumed by
 * "commit()" or removed by "cancel()"
 */
int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
				 struct page *page,
				 gfp_t mask, struct mem_cgroup **ptr)
{
	struct mem_cgroup *mem;
	int ret;

	if (mem_cgroup_disabled())
		return 0;

	if (!do_swap_account)
		goto charge_cur_mm;
	/*
	 * A racing thread's fault, or swapoff, may have already updated
	 * the pte, and even removed page from swap cache: in those cases
	 * do_swap_page()'s pte_same() test will fail; but there's also a
	 * KSM case which does need to charge the page.
	 */
	if (!PageSwapCache(page))
		goto charge_cur_mm;
	mem = try_get_mem_cgroup_from_page(page);
	if (!mem)
		goto charge_cur_mm;
	*ptr = mem;
	ret = __mem_cgroup_try_charge(NULL, mask, ptr, true, PAGE_SIZE);
	css_put(&mem->css);
	return ret;
charge_cur_mm:
	if (unlikely(!mm))
		mm = &init_mm;
	return __mem_cgroup_try_charge(mm, mask, ptr, true, PAGE_SIZE);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
					enum charge_type ctype)
{
	struct page_cgroup *pc;

	if (mem_cgroup_disabled())
		return;
	if (!ptr)
		return;
	cgroup_exclude_rmdir(&ptr->css);
	pc = lookup_page_cgroup(page);
	mem_cgroup_lru_del_before_commit_swapcache(page);
	__mem_cgroup_commit_charge(ptr, pc, ctype, PAGE_SIZE);
	mem_cgroup_lru_add_after_commit_swapcache(page);
	/*
	 * Now swap is on-memory. This means this page may be
	 * counted both as mem and swap....double count.
	 * Fix it by uncharging from memsw. Basically, this SwapCache is stable
	 * under lock_page(). But in do_swap_page()::memory.c, reuse_swap_page()
	 * may call delete_from_swap_cache() before reach here.
	 */
	if (do_swap_account && PageSwapCache(page)) {
		swp_entry_t ent = {.val = page_private(page)};
		unsigned short id;
		struct mem_cgroup *memcg;

		id = swap_cgroup_record(ent, 0);
		rcu_read_lock();
		memcg = mem_cgroup_lookup(id);
		if (memcg) {
			/*
			 * This recorded memcg can be obsolete one. So, avoid
			 * calling css_tryget
			 */
			if (!mem_cgroup_is_root(memcg))
				res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
			mem_cgroup_swap_statistics(memcg, false);
			mem_cgroup_put(memcg);
		}
		rcu_read_unlock();
	}
	/*
	 * At swapin, we may charge account against cgroup which has no tasks.
	 * So, rmdir()->pre_destroy() can be called while we do this charge.
	 * In that case, we need to call pre_destroy() again. check it here.
	 */
	cgroup_release_and_wakeup_rmdir(&ptr->css);
}

void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
{
	__mem_cgroup_commit_charge_swapin(page, ptr,
					MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
{
	if (mem_cgroup_disabled())
		return;
	if (!mem)
		return;
	mem_cgroup_cancel_charge(mem, PAGE_SIZE);
}

static void
__do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
	      int page_size)
{
	struct memcg_batch_info *batch = NULL;
	bool uncharge_memsw = true;
	/* If swapout, usage of swap doesn't decrease */
	if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
		uncharge_memsw = false;

	batch = &current->memcg_batch;
	/*
	 * In usual, we do css_get() when we remember memcg pointer.
	 * But in this case, we keep res->usage until end of a series of
	 * uncharges. Then, it's ok to ignore memcg's refcnt.
	 */
	if (!batch->memcg)
		batch->memcg = mem;
	/*
	 * do_batch > 0 when unmapping pages or inode invalidate/truncate.
	 * In those cases, all pages freed continously can be expected to be in
	 * the same cgroup and we have chance to coalesce uncharges.
	 * But we do uncharge one by one if this is killed by OOM(TIF_MEMDIE)
	 * because we want to do uncharge as soon as possible.
	 */

	if (!batch->do_batch || test_thread_flag(TIF_MEMDIE))
		goto direct_uncharge;

	if (page_size != PAGE_SIZE)
		goto direct_uncharge;

	/*
	 * In typical case, batch->memcg == mem. This means we can
	 * merge a series of uncharges to an uncharge of res_counter.
	 * If not, we uncharge res_counter ony by one.
	 */
	if (batch->memcg != mem)
		goto direct_uncharge;
	/* remember freed charge and uncharge it later */
	batch->bytes += PAGE_SIZE;
	if (uncharge_memsw)
		batch->memsw_bytes += PAGE_SIZE;
	return;
direct_uncharge:
	res_counter_uncharge(&mem->res, page_size);
	if (uncharge_memsw)
		res_counter_uncharge(&mem->memsw, page_size);
	if (unlikely(batch->memcg != mem))
		memcg_oom_recover(mem);
	return;
}

/*
 * uncharge if !page_mapped(page)
 */
static struct mem_cgroup *
__mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
{
	int count;
	struct page_cgroup *pc;
	struct mem_cgroup *mem = NULL;
	int page_size = PAGE_SIZE;

	if (mem_cgroup_disabled())
		return NULL;

	if (PageSwapCache(page))
		return NULL;

	if (PageTransHuge(page)) {
		page_size <<= compound_order(page);
		VM_BUG_ON(!PageTransHuge(page));
	}

	count = page_size >> PAGE_SHIFT;
	/*
	 * Check if our page_cgroup is valid
	 */
	pc = lookup_page_cgroup(page);
	if (unlikely(!pc || !PageCgroupUsed(pc)))
		return NULL;

	lock_page_cgroup(pc);

	mem = pc->mem_cgroup;

	if (!PageCgroupUsed(pc))
		goto unlock_out;

	switch (ctype) {
	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
	case MEM_CGROUP_CHARGE_TYPE_DROP:
		/* See mem_cgroup_prepare_migration() */
		if (page_mapped(page) || PageCgroupMigration(pc))
			goto unlock_out;
		break;
	case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
		if (!PageAnon(page)) {	/* Shared memory */
			if (page->mapping && !page_is_file_cache(page))
				goto unlock_out;
		} else if (page_mapped(page)) /* Anon */
				goto unlock_out;
		break;
	default:
		break;
	}

	mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), -count);

	ClearPageCgroupUsed(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
	 * to be reused (freed soon). Exception is SwapCache, it's handled by
	 * special functions.
	 */

	unlock_page_cgroup(pc);
	/*
	 * even after unlock, we have mem->res.usage here and this memcg
	 * will never be freed.
	 */
	memcg_check_events(mem, page);
	if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
		mem_cgroup_swap_statistics(mem, true);
		mem_cgroup_get(mem);
	}
	if (!mem_cgroup_is_root(mem))
		__do_uncharge(mem, ctype, page_size);

	return mem;

unlock_out:
	unlock_page_cgroup(pc);
	return NULL;
}

void mem_cgroup_uncharge_page(struct page *page)
{
	/* early check. */
	if (page_mapped(page))
		return;
	if (page->mapping && !PageAnon(page))
		return;
	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_uncharge_cache_page(struct page *page)
{
	VM_BUG_ON(page_mapped(page));
	VM_BUG_ON(page->mapping);
	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
}

/*
 * Batch_start/batch_end is called in unmap_page_range/invlidate/trucate.
 * In that cases, pages are freed continuously and we can expect pages
 * are in the same memcg. All these calls itself limits the number of
 * pages freed at once, then uncharge_start/end() is called properly.
 * This may be called prural(2) times in a context,
 */

void mem_cgroup_uncharge_start(void)
{
	current->memcg_batch.do_batch++;
	/* We can do nest. */
	if (current->memcg_batch.do_batch == 1) {
		current->memcg_batch.memcg = NULL;
		current->memcg_batch.bytes = 0;
		current->memcg_batch.memsw_bytes = 0;
	}
}

void mem_cgroup_uncharge_end(void)
{
	struct memcg_batch_info *batch = &current->memcg_batch;

	if (!batch->do_batch)
		return;

	batch->do_batch--;
	if (batch->do_batch) /* If stacked, do nothing. */
		return;

	if (!batch->memcg)
		return;
	/*
	 * This "batch->memcg" is valid without any css_get/put etc...
	 * bacause we hide charges behind us.
	 */
	if (batch->bytes)
		res_counter_uncharge(&batch->memcg->res, batch->bytes);
	if (batch->memsw_bytes)
		res_counter_uncharge(&batch->memcg->memsw, batch->memsw_bytes);
	memcg_oom_recover(batch->memcg);
	/* forget this pointer (for sanity check) */
	batch->memcg = NULL;
}

#ifdef CONFIG_SWAP
/*
 * called after __delete_from_swap_cache() and drop "page" account.
 * memcg information is recorded to swap_cgroup of "ent"
 */
void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
{
	struct mem_cgroup *memcg;
	int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;

	if (!swapout) /* this was a swap cache but the swap is unused ! */
		ctype = MEM_CGROUP_CHARGE_TYPE_DROP;

	memcg = __mem_cgroup_uncharge_common(page, ctype);

	/*
	 * record memcg information,  if swapout && memcg != NULL,
	 * mem_cgroup_get() was called in uncharge().
	 */
	if (do_swap_account && swapout && memcg)
		swap_cgroup_record(ent, css_id(&memcg->css));
}
#endif

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
/*
 * called from swap_entry_free(). remove record in swap_cgroup and
 * uncharge "memsw" account.
 */
void mem_cgroup_uncharge_swap(swp_entry_t ent)
{
	struct mem_cgroup *memcg;
	unsigned short id;

	if (!do_swap_account)
		return;

	id = swap_cgroup_record(ent, 0);
	rcu_read_lock();
	memcg = mem_cgroup_lookup(id);
	if (memcg) {
		/*
		 * We uncharge this because swap is freed.
		 * This memcg can be obsolete one. We avoid calling css_tryget
		 */
		if (!mem_cgroup_is_root(memcg))
			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
		mem_cgroup_swap_statistics(memcg, false);
		mem_cgroup_put(memcg);
	}
	rcu_read_unlock();
}

/**
 * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
 * @entry: swap entry to be moved
 * @from:  mem_cgroup which the entry is moved from
 * @to:  mem_cgroup which the entry is moved to
 * @need_fixup: whether we should fixup res_counters and refcounts.
 *
 * It succeeds only when the swap_cgroup's record for this entry is the same
 * as the mem_cgroup's id of @from.
 *
 * Returns 0 on success, -EINVAL on failure.
 *
 * The caller must have charged to @to, IOW, called res_counter_charge() about
 * both res and memsw, and called css_get().
 */
static int mem_cgroup_move_swap_account(swp_entry_t entry,
		struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
	unsigned short old_id, new_id;

	old_id = css_id(&from->css);
	new_id = css_id(&to->css);

	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
		mem_cgroup_swap_statistics(from, false);
		mem_cgroup_swap_statistics(to, true);
		/*
		 * This function is only called from task migration context now.
		 * It postpones res_counter and refcount handling till the end
		 * of task migration(mem_cgroup_clear_mc()) for performance
		 * improvement. But we cannot postpone mem_cgroup_get(to)
		 * because if the process that has been moved to @to does
		 * swap-in, the refcount of @to might be decreased to 0.
		 */
		mem_cgroup_get(to);
		if (need_fixup) {
			if (!mem_cgroup_is_root(from))
				res_counter_uncharge(&from->memsw, PAGE_SIZE);
			mem_cgroup_put(from);
			/*
			 * we charged both to->res and to->memsw, so we should
			 * uncharge to->res.
			 */
			if (!mem_cgroup_is_root(to))
				res_counter_uncharge(&to->res, PAGE_SIZE);
		}
		return 0;
	}
	return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
		struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
	return -EINVAL;
}
#endif

/*
 * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
 * page belongs to.
 */
int mem_cgroup_prepare_migration(struct page *page,
	struct page *newpage, struct mem_cgroup **ptr)
{
	struct page_cgroup *pc;
	struct mem_cgroup *mem = NULL;
	enum charge_type ctype;
	int ret = 0;

	VM_BUG_ON(PageTransHuge(page));
	if (mem_cgroup_disabled())
		return 0;

	pc = lookup_page_cgroup(page);
	lock_page_cgroup(pc);
	if (PageCgroupUsed(pc)) {
		mem = pc->mem_cgroup;
		css_get(&mem->css);
		/*
		 * At migrating an anonymous page, its mapcount goes down
		 * to 0 and uncharge() will be called. But, even if it's fully
		 * unmapped, migration may fail and this page has to be
		 * charged again. We set MIGRATION flag here and delay uncharge
		 * until end_migration() is called
		 *
		 * Corner Case Thinking
		 * A)
		 * When the old page was mapped as Anon and it's unmap-and-freed
		 * while migration was ongoing.
		 * If unmap finds the old page, uncharge() of it will be delayed
		 * until end_migration(). If unmap finds a new page, it's
		 * uncharged when it make mapcount to be 1->0. If unmap code
		 * finds swap_migration_entry, the new page will not be mapped
		 * and end_migration() will find it(mapcount==0).
		 *
		 * B)
		 * When the old page was mapped but migraion fails, the kernel
		 * remaps it. A charge for it is kept by MIGRATION flag even
		 * if mapcount goes down to 0. We can do remap successfully
		 * without charging it again.
		 *
		 * C)
		 * The "old" page is under lock_page() until the end of
		 * migration, so, the old page itself will not be swapped-out.
		 * If the new page is swapped out before end_migraton, our
		 * hook to usual swap-out path will catch the event.
		 */
		if (PageAnon(page))
			SetPageCgroupMigration(pc);
	}
	unlock_page_cgroup(pc);
	/*
	 * If the page is not charged at this point,
	 * we return here.
	 */
	if (!mem)
		return 0;

	*ptr = mem;
	ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false, PAGE_SIZE);
	css_put(&mem->css);/* drop extra refcnt */
	if (ret || *ptr == NULL) {
		if (PageAnon(page)) {
			lock_page_cgroup(pc);
			ClearPageCgroupMigration(pc);
			unlock_page_cgroup(pc);
			/*
			 * The old page may be fully unmapped while we kept it.
			 */
			mem_cgroup_uncharge_page(page);
		}
		return -ENOMEM;
	}
	/*
	 * We charge new page before it's used/mapped. So, even if unlock_page()
	 * is called before end_migration, we can catch all events on this new
	 * page. In the case new page is migrated but not remapped, new page's
	 * mapcount will be finally 0 and we call uncharge in end_migration().
	 */
	pc = lookup_page_cgroup(newpage);
	if (PageAnon(page))
		ctype = MEM_CGROUP_CHARGE_TYPE_MAPPED;
	else if (page_is_file_cache(page))
		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
	else
		ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
	__mem_cgroup_commit_charge(mem, pc, ctype, PAGE_SIZE);
	return ret;
}

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *mem,
	struct page *oldpage, struct page *newpage, bool migration_ok)
{
	struct page *used, *unused;
	struct page_cgroup *pc;

	if (!mem)
		return;
	/* blocks rmdir() */
	cgroup_exclude_rmdir(&mem->css);
	if (!migration_ok) {
		used = oldpage;
		unused = newpage;
	} else {
		used = newpage;
		unused = oldpage;
	}
	/*
	 * We disallowed uncharge of pages under migration because mapcount
	 * of the page goes down to zero, temporarly.
	 * Clear the flag and check the page should be charged.
	 */
	pc = lookup_page_cgroup(oldpage);
	lock_page_cgroup(pc);
	ClearPageCgroupMigration(pc);
	unlock_page_cgroup(pc);

	__mem_cgroup_uncharge_common(unused, MEM_CGROUP_CHARGE_TYPE_FORCE);

	/*
	 * If a page is a file cache, radix-tree replacement is very atomic
	 * and we can skip this check. When it was an Anon page, its mapcount
	 * goes down to 0. But because we added MIGRATION flage, it's not
	 * uncharged yet. There are several case but page->mapcount check
	 * and USED bit check in mem_cgroup_uncharge_page() will do enough
	 * check. (see prepare_charge() also)
	 */
	if (PageAnon(used))
		mem_cgroup_uncharge_page(used);
	/*
	 * At migration, we may charge account against cgroup which has no
	 * tasks.
	 * So, rmdir()->pre_destroy() can be called while we do this charge.
	 * In that case, we need to call pre_destroy() again. check it here.
	 */
	cgroup_release_and_wakeup_rmdir(&mem->css);
}

/*
 * A call to try to shrink memory usage on charge failure at shmem's swapin.
 * Calling hierarchical_reclaim is not enough because we should update
 * last_oom_jiffies to prevent pagefault_out_of_memory from invoking global OOM.
 * Moreover considering hierarchy, we should reclaim from the mem_over_limit,
 * not from the memcg which this page would be charged to.
 * try_charge_swapin does all of these works properly.
 */
int mem_cgroup_shmem_charge_fallback(struct page *page,
			    struct mm_struct *mm,
			    gfp_t gfp_mask)
{
	struct mem_cgroup *mem = NULL;
	int ret;

	if (mem_cgroup_disabled())
		return 0;

	ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
	if (!ret)
		mem_cgroup_cancel_charge_swapin(mem); /* it does !mem check */