Re: [f2fs-dev] [PATCH] f2fs: skip scanning free nid bitmap of full NAT blocks

[Chao Yu]

On 2017/3/11 2:40, Jaegeuk Kim wrote:
> On 03/10, Kinglong Mee wrote:
>> On 3/1/2017 17:09, Chao Yu wrote:
>>> This patch adds to account free nids for each NAT blocks, and while
>>> scanning all free nid bitmap, do check count and skip lookuping in
>>> full NAT block.
>>>
>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>> ---
>>>  fs/f2fs/debug.c |  1 +
>>>  fs/f2fs/f2fs.h  |  2 ++
>>>  fs/f2fs/node.c  | 34 ++++++++++++++++++++++++++++------
>>>  3 files changed, 31 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
>>> index a77df377e2e8..ee2d0a485fc3 100644
>>> --- a/fs/f2fs/debug.c
>>> +++ b/fs/f2fs/debug.c
>>> @@ -196,6 +196,7 @@ static void update_mem_info(struct f2fs_sb_info *sbi)
>>>  	si->base_mem += (NM_I(sbi)->nat_bits_blocks << F2FS_BLKSIZE_BITS);
>>>  	si->base_mem += NM_I(sbi)->nat_blocks * NAT_ENTRY_BITMAP_SIZE;
>>>  	si->base_mem += NM_I(sbi)->nat_blocks / 8;
>>> +	si->base_mem += NM_I(sbi)->nat_blocks * sizeof(unsigned short);
>>>  
>>>  get_cache:
>>>  	si->cache_mem = 0;
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 7e2924981eeb..c0b33719dfa9 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -557,6 +557,8 @@ struct f2fs_nm_info {
>>>  	struct mutex build_lock;	/* lock for build free nids */
>>>  	unsigned char (*free_nid_bitmap)[NAT_ENTRY_BITMAP_SIZE];
>>>  	unsigned char *nat_block_bitmap;
>>> +	unsigned short *free_nid_count;	/* free nid count of NAT block */
>>> +	spinlock_t free_nid_lock;	/* protect updating of nid count */
>>>  
>>
>> Sorry for my reply so late.
>>
>> Is the free_nid_lock needed here?
>> The free_nid_count should be protected as free_nid_bitmap,
>> but there isn't any lock for free_nid_bitmap.
> 
> update_free_nid_bitmap() is covered by nid_list_lock except scan_nat_page.
> But, it seems build_free_nids() can cover the exception. So, at a glance,
> we don't need free_nid_lock.
> 
> Chao, could you check the whole lock coverage again?

- alloc_nid
				- scan_nat_page
				 - update_free_nid_bitmap (nid in NAT block)
- update_free_nid_bitmap (nid in journal)

There is still a race condition in between alloc_nid and scan_nat_page, how
about use nid_list_lock to cover update_free_nid_bitmap in scan_nat_page as well?

Could you check the following patch?

Thanks,

> 
>> How about atomic? 
> 
> IMO, atomic array would not be a proper way.
> 
> Thanks,
> 
>> The free node ids management seems a little complex now.
>>
>> thanks,
>> Kinglong Mee
>>
>>>  	/* for checkpoint */
>>>  	char *nat_bitmap;		/* NAT bitmap pointer */
>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>>> index 94967171dee8..1a759d45b7e4 100644
>>> --- a/fs/f2fs/node.c
>>> +++ b/fs/f2fs/node.c
>>> @@ -1823,7 +1823,8 @@ static void remove_free_nid(struct f2fs_sb_info *sbi, nid_t nid)
>>>  		kmem_cache_free(free_nid_slab, i);
>>>  }
>>>  
>>> -void update_free_nid_bitmap(struct f2fs_sb_info *sbi, nid_t nid, bool set)
>>> +void update_free_nid_bitmap(struct f2fs_sb_info *sbi, nid_t nid,
>>> +							bool set, bool build)
>>>  {
>>>  	struct f2fs_nm_info *nm_i = NM_I(sbi);
>>>  	unsigned int nat_ofs = NAT_BLOCK_OFFSET(nid);
>>> @@ -1836,6 +1837,13 @@ void update_free_nid_bitmap(struct f2fs_sb_info *sbi, nid_t nid, bool set)
>>>  		set_bit_le(nid_ofs, nm_i->free_nid_bitmap[nat_ofs]);
>>>  	else
>>>  		clear_bit_le(nid_ofs, nm_i->free_nid_bitmap[nat_ofs]);
>>> +
>>> +	spin_lock(&nm_i->free_nid_lock);
>>> +	if (set)
>>> +		nm_i->free_nid_count[nat_ofs]++;
>>> +	else if (!build)
>>> +		nm_i->free_nid_count[nat_ofs]--;
>>> +	spin_unlock(&nm_i->free_nid_lock);
>>>  }
>>>  
>>>  static void scan_nat_page(struct f2fs_sb_info *sbi,
>>> @@ -1847,6 +1855,9 @@ static void scan_nat_page(struct f2fs_sb_info *sbi,
>>>  	unsigned int nat_ofs = NAT_BLOCK_OFFSET(start_nid);
>>>  	int i;
>>>  
>>> +	if (test_bit_le(nat_ofs, nm_i->nat_block_bitmap))
>>> +		return;
>>> +
>>>  	set_bit_le(nat_ofs, nm_i->nat_block_bitmap);
>>>  
>>>  	i = start_nid % NAT_ENTRY_PER_BLOCK;
>>> @@ -1861,7 +1872,7 @@ static void scan_nat_page(struct f2fs_sb_info *sbi,
>>>  		f2fs_bug_on(sbi, blk_addr == NEW_ADDR);
>>>  		if (blk_addr == NULL_ADDR)
>>>  			freed = add_free_nid(sbi, start_nid, true);
>>> -		update_free_nid_bitmap(sbi, start_nid, freed);
>>> +		update_free_nid_bitmap(sbi, start_nid, freed, true);
>>>  	}
>>>  }
>>>  
>>> @@ -1877,6 +1888,8 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>>>  	for (i = 0; i < nm_i->nat_blocks; i++) {
>>>  		if (!test_bit_le(i, nm_i->nat_block_bitmap))
>>>  			continue;
>>> +		if (!nm_i->free_nid_count[i])
>>> +			continue;
>>>  		for (idx = 0; idx < NAT_ENTRY_PER_BLOCK; idx++) {
>>>  			nid_t nid;
>>>  
>>> @@ -2081,7 +2094,7 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
>>>  		__insert_nid_to_list(sbi, i, ALLOC_NID_LIST, false);
>>>  		nm_i->available_nids--;
>>>  
>>> -		update_free_nid_bitmap(sbi, *nid, false);
>>> +		update_free_nid_bitmap(sbi, *nid, false, false);
>>>  
>>>  		spin_unlock(&nm_i->nid_list_lock);
>>>  		return true;
>>> @@ -2137,7 +2150,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
>>>  
>>>  	nm_i->available_nids++;
>>>  
>>> -	update_free_nid_bitmap(sbi, nid, true);
>>> +	update_free_nid_bitmap(sbi, nid, true, false);
>>>  
>>>  	spin_unlock(&nm_i->nid_list_lock);
>>>  
>>> @@ -2467,11 +2480,11 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
>>>  			add_free_nid(sbi, nid, false);
>>>  			spin_lock(&NM_I(sbi)->nid_list_lock);
>>>  			NM_I(sbi)->available_nids++;
>>> -			update_free_nid_bitmap(sbi, nid, true);
>>> +			update_free_nid_bitmap(sbi, nid, true, false);
>>>  			spin_unlock(&NM_I(sbi)->nid_list_lock);
>>>  		} else {
>>>  			spin_lock(&NM_I(sbi)->nid_list_lock);
>>> -			update_free_nid_bitmap(sbi, nid, false);
>>> +			update_free_nid_bitmap(sbi, nid, false, false);
>>>  			spin_unlock(&NM_I(sbi)->nid_list_lock);
>>>  		}
>>>  	}
>>> @@ -2651,6 +2664,14 @@ int init_free_nid_cache(struct f2fs_sb_info *sbi)
>>>  								GFP_KERNEL);
>>>  	if (!nm_i->nat_block_bitmap)
>>>  		return -ENOMEM;
>>> +
>>> +	nm_i->free_nid_count = f2fs_kvzalloc(nm_i->nat_blocks *
>>> +					sizeof(unsigned short), GFP_KERNEL);
>>> +	if (!nm_i->free_nid_count)
>>> +		return -ENOMEM;
>>> +
>>> +	spin_lock_init(&nm_i->free_nid_lock);
>>> +
>>>  	return 0;
>>>  }
>>>  
>>> @@ -2730,6 +2751,7 @@ void destroy_node_manager(struct f2fs_sb_info *sbi)
>>>  
>>>  	kvfree(nm_i->nat_block_bitmap);
>>>  	kvfree(nm_i->free_nid_bitmap);
>>> +	kvfree(nm_i->free_nid_count);
>>>  
>>>  	kfree(nm_i->nat_bitmap);
>>>  	kfree(nm_i->nat_bits);
>>>
> 
> .
>