Date:	Tue, 30 Sep 2014 14:04:20 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	'Jaegeuk Kim' <jaegeuk@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: RE: [f2fs-dev] [PATCH 3/3] f2fs: refactor flush_nat_entries to remove
	costly reorganizing ops

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Tuesday, September 23, 2014 12:53 PM
> To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> linux-f2fs-devel@...ts.sourceforge.net
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 3/3] f2fs: refactor flush_nat_entries to remove costly reorganizing
> ops
> 
> Previously, f2fs tries to reorganize the dirty nat entries into multiple sets
> according to its nid ranges. This can improve the flushing nat pages, however,
> if there are a lot of cached nat entries, it becomes a bottleneck.
> 
> This patch introduces a new set management flow by removing dirty nat list and
> adding a series of set operations when the nat entry becomes dirty.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/f2fs.h |  13 +--
>  fs/f2fs/node.c | 299 +++++++++++++++++++++++++++++----------------------------
>  fs/f2fs/node.h |   9 +-
>  3 files changed, 162 insertions(+), 159 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 7b1e1d2..94cfdc4 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -164,6 +164,9 @@ struct fsync_inode_entry {
>  #define sit_in_journal(sum, i)		(sum->sit_j.entries[i].se)
>  #define segno_in_journal(sum, i)	(sum->sit_j.entries[i].segno)
> 
> +#define MAX_NAT_JENTRIES(sum)	(NAT_JOURNAL_ENTRIES - nats_in_cursum(sum))
> +#define MAX_SIT_JENTRIES(sum)	(SIT_JOURNAL_ENTRIES - sits_in_cursum(sum))
> +
>  static inline int update_nats_in_cursum(struct f2fs_summary_block *rs, int i)
>  {
>  	int before = nats_in_cursum(rs);
> @@ -182,9 +185,8 @@ static inline bool __has_cursum_space(struct f2fs_summary_block *sum, int
> size,
>  								int type)
>  {
>  	if (type == NAT_JOURNAL)
> -		return nats_in_cursum(sum) + size <= NAT_JOURNAL_ENTRIES;
> -
> -	return sits_in_cursum(sum) + size <= SIT_JOURNAL_ENTRIES;
> +		return size <= MAX_NAT_JENTRIES(sum);
> +	return size <= MAX_SIT_JENTRIES(sum);
>  }
> 
>  /*
> @@ -292,11 +294,10 @@ struct f2fs_nm_info {
> 
>  	/* NAT cache management */
>  	struct radix_tree_root nat_root;/* root of the nat entry cache */
> +	struct radix_tree_root nat_set_root;/* root of the nat set cache */
>  	rwlock_t nat_tree_lock;		/* protect nat_tree_lock */
> -	unsigned int nat_cnt;		/* the # of cached nat entries */
>  	struct list_head nat_entries;	/* cached nat entry list (clean) */
> -	struct list_head dirty_nat_entries; /* cached nat entry list (dirty) */
> -	struct list_head nat_entry_set;	/* nat entry set list */
> +	unsigned int nat_cnt;		/* the # of cached nat entries */
>  	unsigned int dirty_nat_cnt;	/* total num of nat entries in set */
> 
>  	/* free node ids management */
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 21ed91b..f5a21f4 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -123,6 +123,57 @@ static void __del_from_nat_cache(struct f2fs_nm_info *nm_i, struct
> nat_entry *e)
>  	kmem_cache_free(nat_entry_slab, e);
>  }
> 
> +static void __set_nat_cache_dirty(struct f2fs_nm_info *nm_i,
> +						struct nat_entry *ne)
> +{
> +	nid_t set = ne->ni.nid / NAT_ENTRY_PER_BLOCK;

nid_t set = NAT_BLOCK_OFFSET(ne->ni.nid);

> +	struct nat_entry_set *head;
> +
> +	if (get_nat_flag(ne, IS_DIRTY))
> +		return;
> +retry:
> +	head = radix_tree_lookup(&nm_i->nat_set_root, set);
> +	if (!head) {
> +		head = f2fs_kmem_cache_alloc(nat_entry_set_slab, GFP_ATOMIC);
> +
> +		INIT_LIST_HEAD(&head->entry_list);
> +		INIT_LIST_HEAD(&head->set_list);
> +		head->set = set;
> +		head->entry_cnt = 0;
> +
> +		if (radix_tree_insert(&nm_i->nat_set_root, set, head)) {
> +			cond_resched();
> +			goto retry;
> +		}
> +	}
> +	list_move_tail(&ne->list, &head->entry_list);
> +	nm_i->dirty_nat_cnt++;
> +	head->entry_cnt++;
> +	set_nat_flag(ne, IS_DIRTY, true);
> +}
> +
> +static void __clear_nat_cache_dirty(struct f2fs_nm_info *nm_i,
> +						struct nat_entry *ne)
> +{
> +	nid_t set = ne->ni.nid / NAT_ENTRY_PER_BLOCK;
> +	struct nat_entry_set *head;
> +
> +	head = radix_tree_lookup(&nm_i->nat_set_root, set);
> +	if (head) {
> +		list_move_tail(&ne->list, &nm_i->nat_entries);
> +		set_nat_flag(ne, IS_DIRTY, false);
> +		head->entry_cnt--;
> +		nm_i->dirty_nat_cnt--;
> +	}
> +}
> +
> +static unsigned int __gang_lookup_nat_set(struct f2fs_nm_info *nm_i,
> +		nid_t start, unsigned int nr, struct nat_entry_set **ep)
> +{
> +	return radix_tree_gang_lookup(&nm_i->nat_set_root, (void **)ep,
> +							start, nr);
> +}
> +
>  bool is_checkpointed_node(struct f2fs_sb_info *sbi, nid_t nid)
>  {
>  	struct f2fs_nm_info *nm_i = NM_I(sbi);
> @@ -1739,79 +1790,6 @@ skip:
>  	return err;
>  }
> 
> -static struct nat_entry_set *grab_nat_entry_set(void)
> -{
> -	struct nat_entry_set *nes =
> -			f2fs_kmem_cache_alloc(nat_entry_set_slab, GFP_ATOMIC);
> -
> -	nes->entry_cnt = 0;
> -	INIT_LIST_HEAD(&nes->set_list);
> -	INIT_LIST_HEAD(&nes->entry_list);
> -	return nes;
> -}
> -
> -static void release_nat_entry_set(struct nat_entry_set *nes,
> -						struct f2fs_nm_info *nm_i)
> -{
> -	nm_i->dirty_nat_cnt -= nes->entry_cnt;
> -	list_del(&nes->set_list);
> -	kmem_cache_free(nat_entry_set_slab, nes);
> -}
> -
> -static void adjust_nat_entry_set(struct nat_entry_set *nes,
> -						struct list_head *head)
> -{
> -	struct nat_entry_set *next = nes;
> -
> -	if (list_is_last(&nes->set_list, head))
> -		return;
> -
> -	list_for_each_entry_continue(next, head, set_list)
> -		if (nes->entry_cnt <= next->entry_cnt)
> -			break;
> -
> -	list_move_tail(&nes->set_list, &next->set_list);
> -}
> -
> -static void add_nat_entry(struct nat_entry *ne, struct list_head *head)
> -{
> -	struct nat_entry_set *nes;
> -	nid_t start_nid = START_NID(ne->ni.nid);
> -
> -	list_for_each_entry(nes, head, set_list) {
> -		if (nes->start_nid == start_nid) {
> -			list_move_tail(&ne->list, &nes->entry_list);
> -			nes->entry_cnt++;
> -			adjust_nat_entry_set(nes, head);
> -			return;
> -		}
> -	}
> -
> -	nes = grab_nat_entry_set();
> -
> -	nes->start_nid = start_nid;
> -	list_move_tail(&ne->list, &nes->entry_list);
> -	nes->entry_cnt++;
> -	list_add(&nes->set_list, head);
> -}
> -
> -static void merge_nats_in_set(struct f2fs_sb_info *sbi)
> -{
> -	struct f2fs_nm_info *nm_i = NM_I(sbi);
> -	struct list_head *dirty_list = &nm_i->dirty_nat_entries;
> -	struct list_head *set_list = &nm_i->nat_entry_set;
> -	struct nat_entry *ne, *tmp;
> -
> -	write_lock(&nm_i->nat_tree_lock);
> -	list_for_each_entry_safe(ne, tmp, dirty_list, list) {
> -		if (nat_get_blkaddr(ne) == NEW_ADDR)
> -			continue;

Shouldn't we move this condition judgment into __flush_nat_entry_set?

> -		add_nat_entry(ne, set_list);
> -		nm_i->dirty_nat_cnt++;
> -	}
> -	write_unlock(&nm_i->nat_tree_lock);
> -}
> -
>  static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
>  {
>  	struct f2fs_nm_info *nm_i = NM_I(sbi);
> @@ -1846,101 +1824,129 @@ found:
>  	mutex_unlock(&curseg->curseg_mutex);
>  }
> 
> -/*
> - * This function is called during the checkpointing process.
> - */
> -void flush_nat_entries(struct f2fs_sb_info *sbi)
> +static void __adjust_nat_entry_set(struct nat_entry_set *nes,
> +						struct list_head *head, int max)
>  {
> -	struct f2fs_nm_info *nm_i = NM_I(sbi);
> -	struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
> -	struct f2fs_summary_block *sum = curseg->sum_blk;
> -	struct nat_entry_set *nes, *tmp;
> -	struct list_head *head = &nm_i->nat_entry_set;
> -	bool to_journal = true;
> +	struct nat_entry_set *cur;
> +	nid_t dirty_cnt = 0;
> 
> -	/* merge nat entries of dirty list to nat entry set temporarily */
> -	merge_nats_in_set(sbi);
> +	if (nes->entry_cnt >= max)
> +		goto add_out;
> 
> -	/*
> -	 * if there are no enough space in journal to store dirty nat
> -	 * entries, remove all entries from journal and merge them
> -	 * into nat entry set.
> -	 */
> -	if (!__has_cursum_space(sum, nm_i->dirty_nat_cnt, NAT_JOURNAL)) {
> -		remove_nats_in_journal(sbi);
> -
> -		/*
> -		 * merge nat entries of dirty list to nat entry set temporarily
> -		 */
> -		merge_nats_in_set(sbi);
> +	list_for_each_entry(cur, head, set_list) {
> +		dirty_cnt += cur->entry_cnt;
> +		if (dirty_cnt > max)
> +			break;

Seems a problem here, For example:
set no:		1	2	3	4	5	6	7
nat number:	4	3	2	1	1	1	1
max = 6
set list will be: 3--4--2--1--1--1--1
Then we will prior flush nat set with more entries in the set list, result in
a degradation.
We'd better not break the adjustment until we finish to traverse the whole
sequential sorted set list to avoid above condition, so how about removing the
codes relate to dirty_cnt?

Thanks,
Yu

> +		if (cur->entry_cnt >= nes->entry_cnt) {
> +			list_add(&nes->set_list, cur->set_list.prev);
> +			return;
> +		}
>  	}
> +add_out:
> +	list_add_tail(&nes->set_list, head);
> +}
> 
> -	if (!nm_i->dirty_nat_cnt)
> -		return;
> +static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> +					struct nat_entry_set *set)
> +{
> +	struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
> +	struct f2fs_summary_block *sum = curseg->sum_blk;
> +	nid_t start_nid = set->set * NAT_ENTRY_PER_BLOCK;
> +	bool to_journal = true;
> +	struct f2fs_nat_block *nat_blk;
> +	struct nat_entry *ne, *cur;
> +	struct page *page = NULL;
> 
>  	/*
>  	 * there are two steps to flush nat entries:
>  	 * #1, flush nat entries to journal in current hot data summary block.
>  	 * #2, flush nat entries to nat page.
>  	 */
> -	list_for_each_entry_safe(nes, tmp, head, set_list) {
> -		struct f2fs_nat_block *nat_blk;
> -		struct nat_entry *ne, *cur;
> -		struct page *page;
> -		nid_t start_nid = nes->start_nid;
> +	if (!__has_cursum_space(sum, set->entry_cnt, NAT_JOURNAL))
> +		to_journal = false;
> 
> -		if (to_journal &&
> -			!__has_cursum_space(sum, nes->entry_cnt, NAT_JOURNAL))
> -			to_journal = false;
> +	if (to_journal) {
> +		mutex_lock(&curseg->curseg_mutex);
> +	} else {
> +		page = get_next_nat_page(sbi, start_nid);
> +		nat_blk = page_address(page);
> +		f2fs_bug_on(sbi, !nat_blk);
> +	}
> +
> +	/* flush dirty nats in nat entry set */
> +	list_for_each_entry_safe(ne, cur, &set->entry_list, list) {
> +		struct f2fs_nat_entry *raw_ne;
> +		nid_t nid = nat_get_nid(ne);
> +		int offset;
> 
>  		if (to_journal) {
> -			mutex_lock(&curseg->curseg_mutex);
> +			offset = lookup_journal_in_cursum(sum,
> +							NAT_JOURNAL, nid, 1);
> +			f2fs_bug_on(sbi, offset < 0);
> +			raw_ne = &nat_in_journal(sum, offset);
> +			nid_in_journal(sum, offset) = cpu_to_le32(nid);
>  		} else {
> -			page = get_next_nat_page(sbi, start_nid);
> -			nat_blk = page_address(page);
> -			f2fs_bug_on(sbi, !nat_blk);
> +			raw_ne = &nat_blk->entries[nid - start_nid];
>  		}
> +		raw_nat_from_node_info(raw_ne, &ne->ni);
> 
> -		/* flush dirty nats in nat entry set */
> -		list_for_each_entry_safe(ne, cur, &nes->entry_list, list) {
> -			struct f2fs_nat_entry *raw_ne;
> -			nid_t nid = nat_get_nid(ne);
> -			int offset;
> +		write_lock(&NM_I(sbi)->nat_tree_lock);
> +		nat_reset_flag(ne);
> +		__clear_nat_cache_dirty(NM_I(sbi), ne);
> +		write_unlock(&NM_I(sbi)->nat_tree_lock);
> 
> -			if (to_journal) {
> -				offset = lookup_journal_in_cursum(sum,
> -							NAT_JOURNAL, nid, 1);
> -				f2fs_bug_on(sbi, offset < 0);
> -				raw_ne = &nat_in_journal(sum, offset);
> -				nid_in_journal(sum, offset) = cpu_to_le32(nid);
> -			} else {
> -				raw_ne = &nat_blk->entries[nid - start_nid];
> -			}
> -			raw_nat_from_node_info(raw_ne, &ne->ni);
> +		if (nat_get_blkaddr(ne) == NULL_ADDR)
> +			add_free_nid(sbi, nid, false);
> +	}
> 
> -			if (nat_get_blkaddr(ne) == NULL_ADDR &&
> -				add_free_nid(sbi, nid, false) <= 0) {
> -				write_lock(&nm_i->nat_tree_lock);
> -				__del_from_nat_cache(nm_i, ne);
> -				write_unlock(&nm_i->nat_tree_lock);
> -			} else {
> -				write_lock(&nm_i->nat_tree_lock);
> -				nat_reset_flag(ne);
> -				__clear_nat_cache_dirty(nm_i, ne);
> -				write_unlock(&nm_i->nat_tree_lock);
> -			}
> -		}
> +	if (to_journal)
> +		mutex_unlock(&curseg->curseg_mutex);
> +	else
> +		f2fs_put_page(page, 1);
> 
> -		if (to_journal)
> -			mutex_unlock(&curseg->curseg_mutex);
> -		else
> -			f2fs_put_page(page, 1);
> +	f2fs_bug_on(sbi, set->entry_cnt);
> +	radix_tree_delete(&NM_I(sbi)->nat_set_root, set->set);
> +	kmem_cache_free(nat_entry_set_slab, set);
> +}
> 
> -		f2fs_bug_on(sbi, !list_empty(&nes->entry_list));
> -		release_nat_entry_set(nes, nm_i);
> +/*
> + * This function is called during the checkpointing process.
> + */
> +void flush_nat_entries(struct f2fs_sb_info *sbi)
> +{
> +	struct f2fs_nm_info *nm_i = NM_I(sbi);
> +	struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
> +	struct f2fs_summary_block *sum = curseg->sum_blk;
> +	struct nat_entry_set *setvec[NATVEC_SIZE];
> +	struct nat_entry_set *set, *tmp;
> +	unsigned int found;
> +	nid_t set_idx = 0;
> +	LIST_HEAD(sets);
> +
> +	/*
> +	 * if there are no enough space in journal to store dirty nat
> +	 * entries, remove all entries from journal and merge them
> +	 * into nat entry set.
> +	 */
> +	if (!__has_cursum_space(sum, nm_i->dirty_nat_cnt, NAT_JOURNAL))
> +		remove_nats_in_journal(sbi);
> +
> +	if (!nm_i->dirty_nat_cnt)
> +		return;
> +
> +	while ((found = __gang_lookup_nat_set(nm_i,
> +					set_idx, NATVEC_SIZE, setvec))) {
> +		unsigned idx;
> +		set_idx = setvec[found - 1]->set + 1;
> +		for (idx = 0; idx < found; idx++)
> +			__adjust_nat_entry_set(setvec[idx], &sets,
> +							MAX_NAT_JENTRIES(sum));
>  	}
> 
> -	f2fs_bug_on(sbi, !list_empty(head));
> +	/* flush dirty nats in nat entry set */
> +	list_for_each_entry_safe(set, tmp, &sets, set_list)
> +		__flush_nat_entry_set(sbi, set);
> +
>  	f2fs_bug_on(sbi, nm_i->dirty_nat_cnt);
>  }
> 
> @@ -1968,9 +1974,8 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
>  	INIT_RADIX_TREE(&nm_i->free_nid_root, GFP_ATOMIC);
>  	INIT_LIST_HEAD(&nm_i->free_nid_list);
>  	INIT_RADIX_TREE(&nm_i->nat_root, GFP_ATOMIC);
> +	INIT_RADIX_TREE(&nm_i->nat_set_root, GFP_ATOMIC);
>  	INIT_LIST_HEAD(&nm_i->nat_entries);
> -	INIT_LIST_HEAD(&nm_i->dirty_nat_entries);
> -	INIT_LIST_HEAD(&nm_i->nat_entry_set);
> 
>  	mutex_init(&nm_i->build_lock);
>  	spin_lock_init(&nm_i->free_nid_list_lock);
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index b8ba63c..bd826d9 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -43,6 +43,7 @@ enum {
>  	IS_CHECKPOINTED,	/* is it checkpointed before? */
>  	HAS_FSYNCED_INODE,	/* is the inode fsynced before? */
>  	HAS_LAST_FSYNC,		/* has the latest node fsync mark? */
> +	IS_DIRTY,		/* this nat entry is dirty? */
>  };
> 
>  struct nat_entry {
> @@ -60,10 +61,6 @@ struct nat_entry {
>  #define nat_get_version(nat)		(nat->ni.version)
>  #define nat_set_version(nat, v)		(nat->ni.version = v)
> 
> -#define __set_nat_cache_dirty(nm_i, ne)					\
> -		list_move_tail(&ne->list, &nm_i->dirty_nat_entries);
> -#define __clear_nat_cache_dirty(nm_i, ne)				\
> -		list_move_tail(&ne->list, &nm_i->nat_entries);
>  #define inc_node_version(version)	(++version)
> 
>  static inline void set_nat_flag(struct nat_entry *ne,
> @@ -113,9 +110,9 @@ enum mem_type {
>  };
> 
>  struct nat_entry_set {
> -	struct list_head set_list;	/* link with all nat sets */
> +	struct list_head set_list;	/* link with other nat sets */
>  	struct list_head entry_list;	/* link with dirty nat entries */
> -	nid_t start_nid;		/* start nid of nats in set */
> +	nid_t set;			/* set number*/
>  	unsigned int entry_cnt;		/* the # of nat entries in set */
>  };
> 
> --
> 1.8.5.2 (Apple Git-48)
> 
> 
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