Re: [f2fs-dev] [PATCH] f2fs: fix to account total free nid correctly

[Chao Yu]

Hi Yunlei,

On 2016/11/17 17:42, heyunlei wrote:
> 
> 
> On 2016/11/15 4:45, Jaegeuk Kim wrote:
>> On Mon, Nov 14, 2016 at 07:24:56PM +0800, Chao Yu wrote:
>>> Thread A		Thread B		Thread C
>>> - f2fs_create
>>>  - f2fs_new_inode
>>>   - f2fs_lock_op
>>>    - alloc_nid
>>>     alloc last nid
>>>   - f2fs_unlock_op
>>> 			- f2fs_create
>>> 			 - f2fs_new_inode
>>> 			  - f2fs_lock_op
>>> 			   - alloc_nid
>>> 			    as node count still not
>>> 			    be increased, we will
>>> 			    loop in alloc_nid
>>> 						- f2fs_write_node_pages
>>> 						 - f2fs_balance_fs_bg
>>> 						  - f2fs_sync_fs
>>> 						   - write_checkpoint
>>> 						    - block_operations
>>> 						     - f2fs_lock_all
>>>  - f2fs_lock_op
>>>
>>> While creating new inode, we do not allocate and account nid atomically,
>>> so that when there is almost no free nids left, we may encounter deadloop
>>> like above stack.
>>>
>>> In order to avoid that, add nm_i::free_nid_cnt for accounting free nids
>>> and do nid allocation atomically during node creation.
>>
>> How about using nm_i::avaiable_nids for this?
>> It seems that we don't need both of variables at the same time.
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>> ---
>>>  fs/f2fs/f2fs.h |  1 +
>>>  fs/f2fs/node.c | 19 +++++++++++++++----
>>>  2 files changed, 16 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 6de1fbf..9de6f20 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -551,6 +551,7 @@ struct f2fs_nm_info {
>>>  	struct radix_tree_root free_nid_root;/* root of the free_nid cache */
>>>  	struct list_head nid_list[MAX_NID_LIST];/* lists for free nids */
>>>  	unsigned int nid_cnt[MAX_NID_LIST];	/* the number of free node id */
>>> +	unsigned int free_nid_cnt;	/* the number of total free nid */
>>>  	spinlock_t nid_list_lock;	/* protect nid lists ops */
>>>  	struct mutex build_lock;	/* lock for build free nids */
>>>
>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>>> index d58438f..e412d0e 100644
>>> --- a/fs/f2fs/node.c
>>> +++ b/fs/f2fs/node.c
>>> @@ -1885,11 +1885,13 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
>>>  		return false;
>>>  	}
>>>  #endif
>>> -	if (unlikely(sbi->total_valid_node_count + 1 > nm_i->available_nids))
>>> -		return false;
>>> -
>>>  	spin_lock(&nm_i->nid_list_lock);
>>>
>>> +	if (unlikely(nm_i->free_nid_cnt == 0)) {
>>> +		spin_unlock(&nm_i->nid_list_lock);
>>> +		return false;
>>> +	}
>>> +
>>>  	/* We should not use stale free nids created by build_free_nids */
>>>  	if (nm_i->nid_cnt[FREE_NID_LIST] && !on_build_free_nids(nm_i)) {
>>>  		f2fs_bug_on(sbi, list_empty(&nm_i->nid_list[FREE_NID_LIST]));
>>> @@ -1900,6 +1902,7 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
>>>  		__remove_nid_from_list(sbi, i, FREE_NID_LIST, true);
>>>  		i->state = NID_ALLOC;
>>>  		__insert_nid_to_list(sbi, i, ALLOC_NID_LIST, false);
>>> +		nm_i->free_nid_cnt--;
>>>  		spin_unlock(&nm_i->nid_list_lock);
>>>  		return true;
>>>  	}
>>> @@ -1951,6 +1954,9 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
>>>  		i->state = NID_NEW;
>>>  		__insert_nid_to_list(sbi, i, FREE_NID_LIST, false);
>>>  	}
>>> +
>>> +	nm_i->free_nid_cnt++;
>>> +
>>>  	spin_unlock(&nm_i->nid_list_lock);
>>>
>>>  	if (need_free)
>>> @@ -2222,8 +2228,12 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
>>>  		raw_nat_from_node_info(raw_ne, &ne->ni);
>>>  		nat_reset_flag(ne);
>>>  		__clear_nat_cache_dirty(NM_I(sbi), ne);
>>> -		if (nat_get_blkaddr(ne) == NULL_ADDR)
>>> +		if (nat_get_blkaddr(ne) == NULL_ADDR) {
>>>  			add_free_nid(sbi, nid, false);
>>> +			spin_lock(&NM_I(sbi)->nid_list_lock);
>>> +			NM_I(sbi)->free_nid_cnt++;
> Hi all,
> 	Here, we should consider clean NULL_ADDR nat entry in journal.
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index dcfab29..b22ecb0 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -158,6 +158,13 @@ static void __set_nat_cache_dirty(struct f2fs_nm_info *nm_i,
>          if (get_nat_flag(ne, IS_DIRTY))
>                  return;
> 
> +       if (ne->ni.blk_addr == NULL_ADDR) {
> +               spin_lock(&nm_i->free_nid_list_lock);
> +               nm_i->available_nids--;
> +               spin_unlock(&nm_i->free_nid_list_lock);
> +       }
> +
> +

Thanks for pointing this out, as we discussed, it should be moved to
remove_nats_in_journal, anyway, I will send v2.

Thanks,

> 
> Thanks.
> 
>>> +			spin_unlock(&NM_I(sbi)->nid_list_lock);
>>> +		}
>>>  	}
>>>
>>>  	if (to_journal)
>>> @@ -2302,6 +2312,7 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
>>>  	nm_i->nid_cnt[FREE_NID_LIST] = 0;
>>>  	nm_i->nid_cnt[ALLOC_NID_LIST] = 0;
>>>  	nm_i->nat_cnt = 0;
>>> +	nm_i->free_nid_cnt = nm_i->available_nids - sbi->total_valid_node_count;
>>>  	nm_i->ram_thresh = DEF_RAM_THRESHOLD;
>>>  	nm_i->ra_nid_pages = DEF_RA_NID_PAGES;
>>>  	nm_i->dirty_nats_ratio = DEF_DIRTY_NAT_RATIO_THRESHOLD;
>>> --
>>> 2.8.2.311.gee88674
>>
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>> .
>>
> 
> 
> .
>