Re: [PATCH RFC] f2fs: combine nat_bits and free_nid_bitmap cache

[Kinglong Mee <kinglongmee@gmail.com>]

On 3/2/2017 09:35, Chao Yu wrote:
> On 2017/3/1 21:09, Kinglong Mee wrote:
>> On 3/1/2017 17:10, Chao Yu wrote:
>>> Both nat_bits cache and free_nid_bitmap cache provide same functionality
>>> as a intermediate cache between free nid cache and disk, but with
>>> different granularity of indicating free nid range, and different
>>> persistence policy. nat_bits cache provides better persistence ability,
>>> and free_nid_bitmap provides better granularity.
>>>
>>> In this patch we combine advantage of both caches, so finally policy of
>>> the intermediate cache would be:
>>> - init: load free nid status from nat_bits into free_nid_bitmap
>>> - lookup: scan free_nid_bitmap before load NAT blocks
>>
>> Why not scan the full_nat_bits/empty_nat_bits before load NAT blocks here?
>> If after an objects shrinker, the cached free nid will be empty quickly.
> 
> Since after this patch, all nids status (free or used) of
> full_nat_bits/empty_nat_bits will be loaded into free_nid_bitmap, so we can just
> check free_nid_bitmap instead of both cache before loading NAT blocks.

Yes, you are right.
I forgot f2fs also updates update_free_nid_bitmap in __flush_nat_entry_set.

thanks,
Kinglong Mee

>>> - update: update free_nid_bitmap in real-time
>>> - persistence: udpate and persist nat_bits in checkpoint
>>>
>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>> ---
>>>  fs/f2fs/node.c | 109 +++++++++++++++++++++------------------------------------
>>>  1 file changed, 39 insertions(+), 70 deletions(-)
>>>
>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>>> index 1a759d45b7e4..6c027b6833f4 100644
>>> --- a/fs/f2fs/node.c
>>> +++ b/fs/f2fs/node.c
>>> @@ -338,9 +338,6 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
>>>  		set_nat_flag(e, IS_CHECKPOINTED, false);
>>>  	__set_nat_cache_dirty(nm_i, e);
>>>  
>>> -	if (enabled_nat_bits(sbi, NULL) && new_blkaddr == NEW_ADDR)
>>> -		clear_bit_le(NAT_BLOCK_OFFSET(ni->nid), nm_i->empty_nat_bits);
>>> -
>>>  	/* update fsync_mark if its inode nat entry is still alive */
>>>  	if (ni->nid != ni->ino)
>>>  		e = __lookup_nat_cache(nm_i, ni->ino);
>>> @@ -1920,58 +1917,6 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>>>  	up_read(&nm_i->nat_tree_lock);
>>>  }
>>>  
>>> -static int scan_nat_bits(struct f2fs_sb_info *sbi)
>>> -{
>>> -	struct f2fs_nm_info *nm_i = NM_I(sbi);
>>> -	struct page *page;
>>> -	unsigned int i = 0;
>>> -	nid_t nid;
>>> -
>>> -	if (!enabled_nat_bits(sbi, NULL))
>>> -		return -EAGAIN;
>>> -
>>> -	down_read(&nm_i->nat_tree_lock);
>>> -check_empty:
>>> -	i = find_next_bit_le(nm_i->empty_nat_bits, nm_i->nat_blocks, i);
>>> -	if (i >= nm_i->nat_blocks) {
>>> -		i = 0;
>>> -		goto check_partial;
>>> -	}
>>> -
>>> -	for (nid = i * NAT_ENTRY_PER_BLOCK; nid < (i + 1) * NAT_ENTRY_PER_BLOCK;
>>> -									nid++) {
>>> -		if (unlikely(nid >= nm_i->max_nid))
>>> -			break;
>>> -		add_free_nid(sbi, nid, true);
>>> -	}
>>> -
>>> -	if (nm_i->nid_cnt[FREE_NID_LIST] >= MAX_FREE_NIDS)
>>> -		goto out;
>>> -	i++;
>>> -	goto check_empty;
>>> -
>>> -check_partial:
>>> -	i = find_next_zero_bit_le(nm_i->full_nat_bits, nm_i->nat_blocks, i);
>>> -	if (i >= nm_i->nat_blocks) {
>>> -		disable_nat_bits(sbi, true);
>>> -		up_read(&nm_i->nat_tree_lock);
>>> -		return -EINVAL;
>>> -	}
>>> -
>>> -	nid = i * NAT_ENTRY_PER_BLOCK;
>>> -	page = get_current_nat_page(sbi, nid);
>>> -	scan_nat_page(sbi, page, nid);
>>> -	f2fs_put_page(page, 1);
>>> -
>>> -	if (nm_i->nid_cnt[FREE_NID_LIST] < MAX_FREE_NIDS) {
>>> -		i++;
>>> -		goto check_partial;
>>> -	}
>>> -out:
>>> -	up_read(&nm_i->nat_tree_lock);
>>> -	return 0;
>>> -}
>>> -
>>>  static void __build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
>>>  {
>>>  	struct f2fs_nm_info *nm_i = NM_I(sbi);
>>> @@ -1993,21 +1938,6 @@ static void __build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
>>>  
>>>  		if (nm_i->nid_cnt[FREE_NID_LIST])
>>>  			return;
>>> -
>>> -		/* try to find free nids with nat_bits */
>>> -		if (!scan_nat_bits(sbi) && nm_i->nid_cnt[FREE_NID_LIST])
>>> -			return;
>>> -	}
>>> -
>>> -	/* find next valid candidate */
>>> -	if (enabled_nat_bits(sbi, NULL)) {
>>> -		int idx = find_next_zero_bit_le(nm_i->full_nat_bits,
>>> -					nm_i->nat_blocks, 0);
>>> -
>>> -		if (idx >= nm_i->nat_blocks)
>>> -			set_sbi_flag(sbi, SBI_NEED_FSCK);
>>> -		else
>>> -			nid = idx * NAT_ENTRY_PER_BLOCK;
>>>  	}
>>>  
>>>  	/* readahead nat pages to be scanned */
>>> @@ -2590,6 +2520,41 @@ static int __get_nat_bitmaps(struct f2fs_sb_info *sbi)
>>>  	return 0;
>>>  }
>>>  
>>> +inline void load_free_nid_bitmap(struct f2fs_sb_info *sbi)
>>> +{
>>> +	struct f2fs_nm_info *nm_i = NM_I(sbi);
>>> +	unsigned int i = 0;
>>> +	nid_t nid, last_nid;
>>> +
>>> +	for (i = 0; i < nm_i->nat_blocks; i++) {
>>> +		i = find_next_bit_le(nm_i->empty_nat_bits, nm_i->nat_blocks, i);
>>> +		if (i >= nm_i->nat_blocks)
>>> +			break;
>>> +
>>> +		set_bit_le(i, nm_i->nat_block_bitmap);
>>> +
>>> +		nid = i * NAT_ENTRY_PER_BLOCK;
>>> +		last_nid = (i + 1) * NAT_ENTRY_PER_BLOCK;
>>> +
>>> +		for (; nid < last_nid; nid++)
>>> +			update_free_nid_bitmap(sbi, nid, true, true);
>>> +	}
>>> +
>>> +	for (i = 0; i < nm_i->nat_blocks; i++) {
>>> +		i = find_next_bit_le(nm_i->full_nat_bits, nm_i->nat_blocks, i);
>>> +		if (i >= nm_i->nat_blocks)
>>> +			break;
>>> +
>>> +		set_bit_le(i, nm_i->nat_block_bitmap);
>>> +
>>> +		nid = i * NAT_ENTRY_PER_BLOCK;
>>> +		last_nid = (i + 1) * NAT_ENTRY_PER_BLOCK;
>>> +
>>> +		for (; nid < last_nid; nid++)
>>> +			update_free_nid_bitmap(sbi, nid, false, true);
>>> +	}
>>> +}
>>> +
>>>  static int init_node_manager(struct f2fs_sb_info *sbi)
>>>  {
>>>  	struct f2fs_super_block *sb_raw = F2FS_RAW_SUPER(sbi);
>>> @@ -2672,6 +2637,10 @@ int init_free_nid_cache(struct f2fs_sb_info *sbi)
>>>  
>>>  	spin_lock_init(&nm_i->free_nid_lock);
>>>  
>>> +	/* load free nid status from nat_bits table */
>>> +	if (enabled_nat_bits(sbi, NULL))
>>> +		load_free_nid_bitmap(sbi);
>>> +
>>>  	return 0;
>>>  }
>>>  
>>>
>>
>> .
>>
> 
> 

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