On 04/20, Chao Yu wrote:
> As most indirect node, dindirect node, and xattr node won't be updated
> after they are created, but inode node and other direct node will change
> more frequently, so store their nat entries mixedly in whole nat table
> will suffer:
> - fragment nat table soon due to different update rate
> - more nat block update due to fragmented nat table
> 
> In order to solve above issue, we're trying to separate whole nat table to
> two part:
> a. Hot free nid area:
>  - range: [nid #0, nid #x)
>  - store node block address for
>    * inode node
>    * other direct node
> b. Cold free nid area:
>  - range: [nid #x, max nid)
>  - store node block address for
>    * indirect node
>    * dindirect node
>    * xattr node
> 
> Allocation strategy example:
> 
> Free nid: '-'
> Used nid: '='
> 
> 1. Initial status:
> Free Nids:    
> |-----------------------------------------------------------------------|
>               ^               ^                                       ^       
>         ^
> Alloc Range:  |---------------|                                       
> |---------------|
>               hot_start       hot_end                                 
> cold_start      cold_end
> 
> 2. Free nids have ran out:
> Free Nids:    
> |===============-----------------------------------------===============|
>               ^               ^                                       ^       
>         ^
> Alloc Range:  |===============|                                       
> |===============|
>               hot_start       hot_end                                 
> cold_start      cold_end
> 
> 3. Expand hot/cold area range:
> Free Nids:    
> |===============-----------------------------------------===============|
>               ^                               ^       ^                       
>         ^
> Alloc Range:  |===============----------------|       
> |----------------===============|
>               hot_start                       hot_end cold_start              
>         cold_end
> 
> 4. Hot free nids have ran out:
> Free Nids:    
> |===============================-------------------------===============|
>               ^                               ^       ^                       
>         ^
> Alloc Range:  |===============================|       
> |----------------===============|
>               hot_start                       hot_end cold_start              
>         cold_end
> 
> 5. Expand hot area range, hot/cold area boundary has been fixed:
> Free Nids:    
> |===============================-------------------------===============|
>               ^                                       ^                       
>         ^
> Alloc Range:  
> |===============================--------|----------------===============|
>               hot_start                               hot_end(cold_start)     
>         cold_end
> 
> Run xfstests with generic/*:
> 
> before
> node_write:   169660
> cp_count:     60118
> node/cp               2.82
> 
> after:
> node_write:   159145
> cp_count:     84501
> node/cp:      2.64

Nice trial tho, I don't see much benefit on this huge patch. I guess we may be
able to find an efficient way to achieve this issue rather than changing whole
stable codes.

How about getting a free nid in the list from head or tail separately?

> 
> Signed-off-by: Chao Yu <yuch...@huawei.com>
> ---
>  fs/f2fs/checkpoint.c |   4 -
>  fs/f2fs/debug.c      |   6 +-
>  fs/f2fs/f2fs.h       |  19 +++-
>  fs/f2fs/inode.c      |   2 +-
>  fs/f2fs/namei.c      |   2 +-
>  fs/f2fs/node.c       | 302 
> ++++++++++++++++++++++++++++++++-------------------
>  fs/f2fs/node.h       |  17 +--
>  fs/f2fs/segment.c    |   8 +-
>  fs/f2fs/shrinker.c   |   3 +-
>  fs/f2fs/xattr.c      |  10 +-
>  10 files changed, 221 insertions(+), 152 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 96785ffc6181..c17feec72c74 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1029,14 +1029,10 @@ int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
>  static void __prepare_cp_block(struct f2fs_sb_info *sbi)
>  {
>       struct f2fs_checkpoint *ckpt = F2FS_CKPT(sbi);
> -     struct f2fs_nm_info *nm_i = NM_I(sbi);
> -     nid_t last_nid = nm_i->next_scan_nid;
>  
> -     next_free_nid(sbi, &last_nid);
>       ckpt->valid_block_count = cpu_to_le64(valid_user_blocks(sbi));
>       ckpt->valid_node_count = cpu_to_le32(valid_node_count(sbi));
>       ckpt->valid_inode_count = cpu_to_le32(valid_inode_count(sbi));
> -     ckpt->next_free_nid = cpu_to_le32(last_nid);
>  }
>  
>  /*
> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> index 7bb036a3bb81..b13c1d4f110f 100644
> --- a/fs/f2fs/debug.c
> +++ b/fs/f2fs/debug.c
> @@ -100,7 +100,8 @@ static void update_general_status(struct f2fs_sb_info 
> *sbi)
>       si->dirty_nats = NM_I(sbi)->dirty_nat_cnt;
>       si->sits = MAIN_SEGS(sbi);
>       si->dirty_sits = SIT_I(sbi)->dirty_sentries;
> -     si->free_nids = NM_I(sbi)->nid_cnt[FREE_NID];
> +     si->free_nids = NM_I(sbi)->nid_cnt[FREE_HOT_NID] +
> +                             NM_I(sbi)->nid_cnt[FREE_COLD_NID];
>       si->avail_nids = NM_I(sbi)->available_nids;
>       si->alloc_nids = NM_I(sbi)->nid_cnt[PREALLOC_NID];
>       si->bg_gc = sbi->bg_gc;
> @@ -235,7 +236,8 @@ static void update_mem_info(struct f2fs_sb_info *sbi)
>       }
>  
>       /* free nids */
> -     si->cache_mem += (NM_I(sbi)->nid_cnt[FREE_NID] +
> +     si->cache_mem += (NM_I(sbi)->nid_cnt[FREE_HOT_NID] +
> +                             NM_I(sbi)->nid_cnt[FREE_COLD_NID] +
>                               NM_I(sbi)->nid_cnt[PREALLOC_NID]) *
>                               sizeof(struct free_nid);
>       si->cache_mem += NM_I(sbi)->nat_cnt * sizeof(struct nat_entry);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index de1af8dc19e5..9e2b4f84b1b2 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -739,8 +739,11 @@ static inline void __try_update_largest_extent(struct 
> inode *inode,
>   * For free nid management
>   */
>  enum nid_state {
> -     FREE_NID,               /* newly added to free nid list */
> -     PREALLOC_NID,           /* it is preallocated */
> +     FREE_HOT_NID,                   /* list with hot type free nids */
> +     FREE_COLD_NID,                  /* list with cold type free nid */
> +     MAX_NID_TYPE,
> +     INVALID_NID_TYPE = MAX_NID_TYPE,
> +     PREALLOC_NID = MAX_NID_TYPE,    /* it is preallocated */
>       MAX_NID_STATE,
>  };
>  
> @@ -764,8 +767,10 @@ struct f2fs_nm_info {
>  
>       /* free node ids management */
>       struct radix_tree_root free_nid_root;/* root of the free_nid cache */
> -     struct list_head free_nid_list;         /* list for free nids excluding 
> preallocated nids */
> +     struct list_head free_nid_list[MAX_NID_TYPE];   /* list for free nids 
> excluding preallocated nids */
>       unsigned int nid_cnt[MAX_NID_STATE];    /* the number of free node id */
> +     unsigned int nat_block_start[MAX_NID_TYPE];     /* nat block start 
> position */
> +     unsigned int nat_block_end[MAX_NID_TYPE];       /* nat block end 
> position */
>       spinlock_t nid_list_lock;       /* protect nid lists ops */
>       struct mutex build_lock;        /* lock for build free nids */
>       unsigned char **free_nid_bitmap;
> @@ -2796,10 +2801,12 @@ int fsync_node_pages(struct f2fs_sb_info *sbi, struct 
> inode *inode,
>                       struct writeback_control *wbc, bool atomic);
>  int sync_node_pages(struct f2fs_sb_info *sbi, struct writeback_control *wbc,
>                       bool do_balance, enum iostat_type io_type);
> -void build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount);
> -bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid);
> +bool build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount,
> +                                             enum nid_state state);
> +enum nid_state default_free_nid_type(struct f2fs_sb_info *sbi, nid_t nid);
> +int alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid, enum nid_state state);
>  void alloc_nid_done(struct f2fs_sb_info *sbi, nid_t nid);
> -void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid);
> +void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid, enum nid_state 
> state);
>  int try_to_free_nids(struct f2fs_sb_info *sbi, int nr_shrink);
>  void recover_inline_xattr(struct inode *inode, struct page *page);
>  int recover_xattr_data(struct inode *inode, struct page *page);
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 176f8e84bb6e..e9e1ee6c3ba1 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -585,7 +585,7 @@ void f2fs_evict_inode(struct inode *inode)
>                       add_ino_entry(sbi, inode->i_ino, UPDATE_INO);
>       }
>       if (is_inode_flag_set(inode, FI_FREE_NID)) {
> -             alloc_nid_failed(sbi, inode->i_ino);
> +             alloc_nid_failed(sbi, inode->i_ino, FREE_HOT_NID);
>               clear_inode_flag(inode, FI_FREE_NID);
>       } else {
>               f2fs_bug_on(sbi, err &&
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index b5f404674cad..c049076c49e2 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -37,7 +37,7 @@ static struct inode *f2fs_new_inode(struct inode *dir, 
> umode_t mode)
>               return ERR_PTR(-ENOMEM);
>  
>       f2fs_lock_op(sbi);
> -     if (!alloc_nid(sbi, &ino)) {
> +     if (!alloc_nid(sbi, &ino, FREE_HOT_NID)) {
>               f2fs_unlock_op(sbi);
>               err = -ENOSPC;
>               goto fail;
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index bbf2c3441ac0..6b74bff5cdc1 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -46,7 +46,8 @@ bool available_free_memory(struct f2fs_sb_info *sbi, int 
> type)
>        * give 25%, 25%, 50%, 50%, 50% memory for each components respectively
>        */
>       if (type == FREE_NIDS) {
> -             mem_size = (nm_i->nid_cnt[FREE_NID] *
> +             mem_size = ((nm_i->nid_cnt[FREE_HOT_NID] +
> +                             nm_i->nid_cnt[FREE_COLD_NID]) *
>                               sizeof(struct free_nid)) >> PAGE_SHIFT;
>               res = mem_size < ((avail_ram * nm_i->ram_thresh / 100) >> 2);
>       } else if (type == NAT_ENTRIES) {
> @@ -651,10 +652,13 @@ int get_dnode_of_data(struct dnode_of_data *dn, pgoff_t 
> index, int mode)
>       /* get indirect or direct nodes */
>       for (i = 1; i <= level; i++) {
>               bool done = false;
> +             enum nid_state state;
> +
> +             state = (i == 1) ? FREE_HOT_NID : FREE_COLD_NID;
>  
>               if (!nids[i] && mode == ALLOC_NODE) {
>                       /* alloc new node */
> -                     if (!alloc_nid(sbi, &(nids[i]))) {
> +                     if (!alloc_nid(sbi, &(nids[i]), state)) {
>                               err = -ENOSPC;
>                               goto release_pages;
>                       }
> @@ -662,7 +666,7 @@ int get_dnode_of_data(struct dnode_of_data *dn, pgoff_t 
> index, int mode)
>                       dn->nid = nids[i];
>                       npage[i] = new_node_page(dn, noffset[i]);
>                       if (IS_ERR(npage[i])) {
> -                             alloc_nid_failed(sbi, nids[i]);
> +                             alloc_nid_failed(sbi, nids[i], state);
>                               err = PTR_ERR(npage[i]);
>                               goto release_pages;
>                       }
> @@ -1796,10 +1800,9 @@ static int __insert_free_nid(struct f2fs_sb_info *sbi,
>       if (err)
>               return err;
>  
> -     f2fs_bug_on(sbi, state != i->state);
>       nm_i->nid_cnt[state]++;
> -     if (state == FREE_NID)
> -             list_add_tail(&i->list, &nm_i->free_nid_list);
> +     if (state < MAX_NID_TYPE)
> +             list_add_tail(&i->list, &nm_i->free_nid_list[state]);
>       return 0;
>  }
>  
> @@ -1808,9 +1811,8 @@ static void __remove_free_nid(struct f2fs_sb_info *sbi,
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>  
> -     f2fs_bug_on(sbi, state != i->state);
>       nm_i->nid_cnt[state]--;
> -     if (state == FREE_NID)
> +     if (state < MAX_NID_TYPE)
>               list_del(&i->list);
>       radix_tree_delete(&nm_i->free_nid_root, i->nid);
>  }
> @@ -1820,7 +1822,6 @@ static void __move_free_nid(struct f2fs_sb_info *sbi, 
> struct free_nid *i,
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>  
> -     f2fs_bug_on(sbi, org_state != i->state);
>       i->state = dst_state;
>       nm_i->nid_cnt[org_state]--;
>       nm_i->nid_cnt[dst_state]++;
> @@ -1829,8 +1830,9 @@ static void __move_free_nid(struct f2fs_sb_info *sbi, 
> struct free_nid *i,
>       case PREALLOC_NID:
>               list_del(&i->list);
>               break;
> -     case FREE_NID:
> -             list_add_tail(&i->list, &nm_i->free_nid_list);
> +     case FREE_HOT_NID:
> +     case FREE_COLD_NID:
> +             list_add_tail(&i->list, &nm_i->free_nid_list[dst_state]);
>               break;
>       default:
>               BUG_ON(1);
> @@ -1862,8 +1864,8 @@ static void update_free_nid_bitmap(struct f2fs_sb_info 
> *sbi, nid_t nid,
>  }
>  
>  /* return if the nid is recognized as free */
> -static bool add_free_nid(struct f2fs_sb_info *sbi,
> -                             nid_t nid, bool build, bool update)
> +static bool add_free_nid(struct f2fs_sb_info *sbi, nid_t nid, bool build,
> +                                     bool update, enum nid_state state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       struct free_nid *i, *e;
> @@ -1877,7 +1879,7 @@ static bool add_free_nid(struct f2fs_sb_info *sbi,
>  
>       i = f2fs_kmem_cache_alloc(free_nid_slab, GFP_NOFS);
>       i->nid = nid;
> -     i->state = FREE_NID;
> +     i->state = state;
>  
>       radix_tree_preload(GFP_NOFS | __GFP_NOFAIL);
>  
> @@ -1912,13 +1914,14 @@ static bool add_free_nid(struct f2fs_sb_info *sbi,
>  
>               e = __lookup_free_nid_list(nm_i, nid);
>               if (e) {
> -                     if (e->state == FREE_NID)
> +                     if (e->state < MAX_NID_TYPE)
>                               ret = true;
>                       goto err_out;
>               }
>       }
>       ret = true;
> -     err = __insert_free_nid(sbi, i, FREE_NID);
> +     if (state < MAX_NID_TYPE)
> +             err = __insert_free_nid(sbi, i, state);
>  err_out:
>       if (update) {
>               update_free_nid_bitmap(sbi, nid, ret, build);
> @@ -1941,8 +1944,8 @@ static void remove_free_nid(struct f2fs_sb_info *sbi, 
> nid_t nid)
>  
>       spin_lock(&nm_i->nid_list_lock);
>       i = __lookup_free_nid_list(nm_i, nid);
> -     if (i && i->state == FREE_NID) {
> -             __remove_free_nid(sbi, i, FREE_NID);
> +     if (i && i->state < MAX_NID_TYPE) {
> +             __remove_free_nid(sbi, i, i->state);
>               need_free = true;
>       }
>       spin_unlock(&nm_i->nid_list_lock);
> @@ -1951,36 +1954,33 @@ static void remove_free_nid(struct f2fs_sb_info *sbi, 
> nid_t nid)
>               kmem_cache_free(free_nid_slab, i);
>  }
>  
> -static void scan_nat_page(struct f2fs_sb_info *sbi,
> -                     struct page *nat_page, nid_t start_nid)
> +static void scan_nat_page(struct f2fs_sb_info *sbi, struct page *nat_page,
> +                             unsigned int nat_ofs, enum nid_state state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       struct f2fs_nat_block *nat_blk = page_address(nat_page);
> -     block_t blk_addr;
> -     unsigned int nat_ofs = NAT_BLOCK_OFFSET(start_nid);
> +     nid_t nid = nat_ofs * NAT_ENTRY_PER_BLOCK;
>       int i;
>  
>       __set_bit_le(nat_ofs, nm_i->nat_block_bitmap);
>  
> -     i = start_nid % NAT_ENTRY_PER_BLOCK;
> -
> -     for (; i < NAT_ENTRY_PER_BLOCK; i++, start_nid++) {
> -             if (unlikely(start_nid >= nm_i->max_nid))
> -                     break;
> +     for (i = 0; i < NAT_ENTRY_PER_BLOCK; i++, nid++) {
> +             block_t blk_addr = le32_to_cpu(nat_blk->entries[i].block_addr);
>  
> -             blk_addr = le32_to_cpu(nat_blk->entries[i].block_addr);
>               f2fs_bug_on(sbi, blk_addr == NEW_ADDR);
> +
>               if (blk_addr == NULL_ADDR) {
> -                     add_free_nid(sbi, start_nid, true, true);
> +                     add_free_nid(sbi, nid, true, true, state);
>               } else {
>                       spin_lock(&NM_I(sbi)->nid_list_lock);
> -                     update_free_nid_bitmap(sbi, start_nid, false, true);
> +                     update_free_nid_bitmap(sbi, nid, false, true);
>                       spin_unlock(&NM_I(sbi)->nid_list_lock);
>               }
>       }
>  }
>  
> -static void scan_curseg_cache(struct f2fs_sb_info *sbi)
> +static void scan_curseg_cache(struct f2fs_sb_info *sbi,
> +                                             enum nid_state state)
>  {
>       struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
>       struct f2fs_journal *journal = curseg->journal;
> @@ -1994,14 +1994,14 @@ static void scan_curseg_cache(struct f2fs_sb_info 
> *sbi)
>               addr = le32_to_cpu(nat_in_journal(journal, i).block_addr);
>               nid = le32_to_cpu(nid_in_journal(journal, i));
>               if (addr == NULL_ADDR)
> -                     add_free_nid(sbi, nid, true, false);
> +                     add_free_nid(sbi, nid, true, false, state);
>               else
>                       remove_free_nid(sbi, nid);
>       }
>       up_read(&curseg->journal_rwsem);
>  }
>  
> -static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
> +static void scan_free_nid_bits(struct f2fs_sb_info *sbi, enum nid_state 
> state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       unsigned int i, idx;
> @@ -2010,6 +2010,9 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>       down_read(&nm_i->nat_tree_lock);
>  
>       for (i = 0; i < nm_i->nat_blocks; i++) {
> +             if (i < nm_i->nat_block_start[state] ||
> +                             i >= nm_i->nat_block_end[state])
> +                     continue;
>               if (!test_bit_le(i, nm_i->nat_block_bitmap))
>                       continue;
>               if (!nm_i->free_nid_count[i])
> @@ -2021,90 +2024,124 @@ static void scan_free_nid_bits(struct f2fs_sb_info 
> *sbi)
>                               break;
>  
>                       nid = i * NAT_ENTRY_PER_BLOCK + idx;
> -                     add_free_nid(sbi, nid, true, false);
> +                     add_free_nid(sbi, nid, true, false, state);
>  
> -                     if (nm_i->nid_cnt[FREE_NID] >= MAX_FREE_NIDS)
> +                     if (nm_i->nid_cnt[state] >= MAX_FREE_NIDS)
>                               goto out;
>               }
>       }
>  out:
> -     scan_curseg_cache(sbi);
> +     scan_curseg_cache(sbi, state);
>  
>       up_read(&nm_i->nat_tree_lock);
>  }
>  
> -static void __build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool 
> mount)
> +void load_nat_block(struct f2fs_sb_info *sbi, enum nid_state state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
> -     int i = 0;
> -     nid_t nid = nm_i->next_scan_nid;
> +     unsigned int nat_ofs;
> +     unsigned int count = FREE_NID_PAGES;
>  
> -     if (unlikely(nid >= nm_i->max_nid))
> -             nid = 0;
> +     if (state == FREE_HOT_NID) {
> +             nat_ofs = nm_i->nat_block_end[FREE_HOT_NID];
> +             nm_i->nat_block_end[FREE_HOT_NID] += count;
> +     } else {
> +             nm_i->nat_block_start[FREE_COLD_NID] -= count;
> +             nat_ofs = nm_i->nat_block_start[FREE_COLD_NID];
> +     }
>  
> -     /* Enough entries */
> -     if (nm_i->nid_cnt[FREE_NID] >= NAT_ENTRY_PER_BLOCK)
> -             return;
> +     f2fs_bug_on(sbi, nm_i->nat_block_end[FREE_HOT_NID] >
> +                             nm_i->nat_block_start[FREE_COLD_NID]);
>  
> -     if (!sync && !available_free_memory(sbi, FREE_NIDS))
> -             return;
> +     /* readahead nat pages to be scanned */
> +     ra_meta_pages(sbi, nat_ofs, count, META_NAT, true);
>  
> -     if (!mount) {
> -             /* try to find free nids in free_nid_bitmap */
> -             scan_free_nid_bits(sbi);
> +     for (; count > 0; count--, nat_ofs++) {
> +             struct page *page;
>  
> -             if (nm_i->nid_cnt[FREE_NID] >= NAT_ENTRY_PER_BLOCK)
> -                     return;
> +             if (test_bit_le(nat_ofs, nm_i->nat_block_bitmap))
> +                     continue;
> +
> +             page = get_current_nat_page(sbi, nat_ofs * NAT_ENTRY_PER_BLOCK);
> +             scan_nat_page(sbi, page, nat_ofs, state);
> +             f2fs_put_page(page, 1);
>       }
> +}
>  
> -     /* readahead nat pages to be scanned */
> -     ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), FREE_NID_PAGES,
> -                                                     META_NAT, true);
> +static bool __build_free_nids(struct f2fs_sb_info *sbi, bool sync,
> +                                     bool mount, enum nid_state state)
> +{
> +     struct f2fs_nm_info *nm_i = NM_I(sbi);
>  
> -     down_read(&nm_i->nat_tree_lock);
> +     if (nm_i->nid_cnt[state])
> +             return false;
>  
> -     while (1) {
> -             if (!test_bit_le(NAT_BLOCK_OFFSET(nid),
> -                                             nm_i->nat_block_bitmap)) {
> -                     struct page *page = get_current_nat_page(sbi, nid);
> +     if (!sync && !available_free_memory(sbi, FREE_NIDS))
> +             return false;
>  
> -                     scan_nat_page(sbi, page, nid);
> -                     f2fs_put_page(page, 1);
> -             }
> +     if (!mount) {
> +             /* try to find free nids in free_nid_bitmap */
> +             scan_free_nid_bits(sbi, state);
>  
> -             nid += (NAT_ENTRY_PER_BLOCK - (nid % NAT_ENTRY_PER_BLOCK));
> -             if (unlikely(nid >= nm_i->max_nid))
> -                     nid = 0;
> +             if (nm_i->nid_cnt[state])
> +                     return false;
>  
> -             if (++i >= FREE_NID_PAGES)
> -                     break;
> +             /* all nat blocks have been scanned */
> +             if (nm_i->nat_block_end[FREE_HOT_NID] >=
> +                             nm_i->nat_block_start[FREE_COLD_NID])
> +                     return true;
>       }
>  
> -     /* go to the next free nat pages to find free nids abundantly */
> -     nm_i->next_scan_nid = nid;
> +     down_read(&nm_i->nat_tree_lock);
> +
> +     /* find free nids from nat blocks */
> +     load_nat_block(sbi, state);
>  
>       /* find free nids from current sum_pages */
> -     scan_curseg_cache(sbi);
> +     scan_curseg_cache(sbi, state);
>  
>       up_read(&nm_i->nat_tree_lock);
>  
> -     ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nm_i->next_scan_nid),
> -                                     nm_i->ra_nid_pages, META_NAT, false);
> +     return false;
>  }
>  
> -void build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
> +bool build_free_nids(struct f2fs_sb_info *sbi, bool sync,
> +                                     bool mount, enum nid_state state)
>  {
> +     bool exhausted;
> +
>       mutex_lock(&NM_I(sbi)->build_lock);
> -     __build_free_nids(sbi, sync, mount);
> +     exhausted = __build_free_nids(sbi, sync, mount, state);
>       mutex_unlock(&NM_I(sbi)->build_lock);
> +
> +     return exhausted;
>  }
>  
> -/*
> - * If this function returns success, caller can obtain a new nid
> - * from second parameter of this function.
> - * The returned nid could be used ino as well as nid when inode is created.
> - */
> -bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
> +enum nid_state default_free_nid_type(struct f2fs_sb_info *sbi, nid_t nid)
> +{
> +     struct f2fs_nm_info *nm_i = NM_I(sbi);
> +     unsigned int hot_start = nm_i->nat_block_start[FREE_HOT_NID];
> +     unsigned int hot_end = nm_i->nat_block_end[FREE_HOT_NID];
> +     unsigned int cold_start = nm_i->nat_block_start[FREE_COLD_NID];
> +     unsigned int cold_end = nm_i->nat_block_end[FREE_COLD_NID];
> +
> +     if (hot_start != hot_end) {
> +             if (nid >= hot_start * NAT_ENTRY_PER_BLOCK &&
> +                     nid < hot_end * NAT_ENTRY_PER_BLOCK)
> +                     return FREE_HOT_NID;
> +     }
> +
> +     if (cold_start != cold_end) {
> +             if (nid >= cold_start * NAT_ENTRY_PER_BLOCK &&
> +                     nid < cold_end * NAT_ENTRY_PER_BLOCK)
> +                     return FREE_COLD_NID;
> +     }
> +
> +     return INVALID_NID_TYPE;
> +}
> +
> +static int __alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid,
> +                                             enum nid_state state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       struct free_nid *i = NULL;
> @@ -2112,38 +2149,61 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
>  #ifdef CONFIG_F2FS_FAULT_INJECTION
>       if (time_to_inject(sbi, FAULT_ALLOC_NID)) {
>               f2fs_show_injection_info(FAULT_ALLOC_NID);
> -             return false;
> +             return 0;
>       }
>  #endif
>       spin_lock(&nm_i->nid_list_lock);
>  
>       if (unlikely(nm_i->available_nids == 0)) {
>               spin_unlock(&nm_i->nid_list_lock);
> -             return false;
> +             return 0;
>       }
>  
>       /* We should not use stale free nids created by build_free_nids */
> -     if (nm_i->nid_cnt[FREE_NID] && !on_build_free_nids(nm_i)) {
> -             f2fs_bug_on(sbi, list_empty(&nm_i->free_nid_list));
> -             i = list_first_entry(&nm_i->free_nid_list,
> +     if (nm_i->nid_cnt[state] && !on_build_free_nids(nm_i)) {
> +             f2fs_bug_on(sbi, list_empty(&nm_i->free_nid_list[state]));
> +             i = list_first_entry(&nm_i->free_nid_list[state],
>                                       struct free_nid, list);
>               *nid = i->nid;
>  
> -             __move_free_nid(sbi, i, FREE_NID, PREALLOC_NID);
> +             __move_free_nid(sbi, i, state, PREALLOC_NID);
>               nm_i->available_nids--;
>  
>               update_free_nid_bitmap(sbi, *nid, false, false);
>  
>               spin_unlock(&nm_i->nid_list_lock);
> -             return true;
> +
> +             f2fs_bug_on(sbi, *nid >= nm_i->max_nid);
> +             return 1;
>       }
>       spin_unlock(&nm_i->nid_list_lock);
>  
>       /* Let's scan nat pages and its caches to get free nids */
> -     build_free_nids(sbi, true, false);
> +     if (build_free_nids(sbi, true, false, state))
> +             return -1;
>       goto retry;
>  }
>  
> +/*
> + * If this function returns success, caller can obtain a new nid
> + * from second parameter of this function.
> + * The returned nid could be used ino as well as nid when inode is created.
> + */
> +int alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid, enum nid_state state)
> +{
> +     int ret;
> +
> +     ret = __alloc_nid(sbi, nid, state);
> +     if (ret >= 0)
> +             return ret;
> +
> +     ret = __alloc_nid(sbi, nid, !state);
> +     if (ret < 0)
> +             ret = 0;
> +
> +     return ret;
> +}
> +
>  /*
>   * alloc_nid() should be called prior to this function.
>   */
> @@ -2164,7 +2224,8 @@ void alloc_nid_done(struct f2fs_sb_info *sbi, nid_t nid)
>  /*
>   * alloc_nid() should be called prior to this function.
>   */
> -void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
> +void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid,
> +                                             enum nid_state state)
>  {
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       struct free_nid *i;
> @@ -2181,7 +2242,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t 
> nid)
>               __remove_free_nid(sbi, i, PREALLOC_NID);
>               need_free = true;
>       } else {
> -             __move_free_nid(sbi, i, PREALLOC_NID, FREE_NID);
> +             __move_free_nid(sbi, i, PREALLOC_NID, state);
>       }
>  
>       nm_i->available_nids++;
> @@ -2199,22 +2260,23 @@ int try_to_free_nids(struct f2fs_sb_info *sbi, int 
> nr_shrink)
>       struct f2fs_nm_info *nm_i = NM_I(sbi);
>       struct free_nid *i, *next;
>       int nr = nr_shrink;
> -
> -     if (nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> -             return 0;
> +     enum nid_state state;
>  
>       if (!mutex_trylock(&nm_i->build_lock))
>               return 0;
>  
>       spin_lock(&nm_i->nid_list_lock);
> -     list_for_each_entry_safe(i, next, &nm_i->free_nid_list, list) {
> -             if (nr_shrink <= 0 ||
> -                             nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> -                     break;
> +     for (state = FREE_HOT_NID; state < MAX_NID_TYPE; state++) {
> +             list_for_each_entry_safe(i, next,
> +                             &nm_i->free_nid_list[state], list) {
> +                     if (nr_shrink <= 0 ||
> +                             nm_i->nid_cnt[state] <= MAX_FREE_NIDS)
> +                             break;
>  
> -             __remove_free_nid(sbi, i, FREE_NID);
> -             kmem_cache_free(free_nid_slab, i);
> -             nr_shrink--;
> +                     __remove_free_nid(sbi, i, state);
> +                     kmem_cache_free(free_nid_slab, i);
> +                     nr_shrink--;
> +             }
>       }
>       spin_unlock(&nm_i->nid_list_lock);
>       mutex_unlock(&nm_i->build_lock);
> @@ -2271,13 +2333,13 @@ int recover_xattr_data(struct inode *inode, struct 
> page *page)
>  
>  recover_xnid:
>       /* 2: update xattr nid in inode */
> -     if (!alloc_nid(sbi, &new_xnid))
> +     if (!alloc_nid(sbi, &new_xnid, FREE_COLD_NID))
>               return -ENOSPC;
>  
>       set_new_dnode(&dn, inode, NULL, NULL, new_xnid);
>       xpage = new_node_page(&dn, XATTR_NODE_OFFSET);
>       if (IS_ERR(xpage)) {
> -             alloc_nid_failed(sbi, new_xnid);
> +             alloc_nid_failed(sbi, new_xnid, FREE_COLD_NID);
>               return PTR_ERR(xpage);
>       }
>  
> @@ -2532,7 +2594,9 @@ static void __flush_nat_entry_set(struct f2fs_sb_info 
> *sbi,
>               nat_reset_flag(ne);
>               __clear_nat_cache_dirty(NM_I(sbi), set, ne);
>               if (nat_get_blkaddr(ne) == NULL_ADDR) {
> -                     add_free_nid(sbi, nid, false, true);
> +                     enum nid_state state = default_free_nid_type(sbi, nid);
> +
> +                     add_free_nid(sbi, nid, false, true, state);
>               } else {
>                       spin_lock(&NM_I(sbi)->nid_list_lock);
>                       update_free_nid_bitmap(sbi, nid, false, false);
> @@ -2691,15 +2755,21 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
>       /* not used nids: 0, node, meta, (and root counted as valid node) */
>       nm_i->available_nids = nm_i->max_nid - sbi->total_valid_node_count -
>                               sbi->nquota_files - F2FS_RESERVED_NODE_NUM;
> -     nm_i->nid_cnt[FREE_NID] = 0;
> +     nm_i->nid_cnt[FREE_HOT_NID] = 0;
> +     nm_i->nid_cnt[FREE_COLD_NID] = 0;
>       nm_i->nid_cnt[PREALLOC_NID] = 0;
> +     nm_i->nat_block_start[FREE_HOT_NID] =
> +                     nm_i->nat_block_end[FREE_HOT_NID] = 0;
> +     nm_i->nat_block_start[FREE_COLD_NID] =
> +                     nm_i->nat_block_end[FREE_COLD_NID] = nm_i->nat_blocks;
>       nm_i->nat_cnt = 0;
>       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;
>  
>       INIT_RADIX_TREE(&nm_i->free_nid_root, GFP_ATOMIC);
> -     INIT_LIST_HEAD(&nm_i->free_nid_list);
> +     INIT_LIST_HEAD(&nm_i->free_nid_list[FREE_HOT_NID]);
> +     INIT_LIST_HEAD(&nm_i->free_nid_list[FREE_COLD_NID]);
>       INIT_RADIX_TREE(&nm_i->nat_root, GFP_NOIO);
>       INIT_RADIX_TREE(&nm_i->nat_set_root, GFP_NOIO);
>       INIT_LIST_HEAD(&nm_i->nat_entries);
> @@ -2782,7 +2852,8 @@ int build_node_manager(struct f2fs_sb_info *sbi)
>       /* load free nid status from nat_bits table */
>       load_free_nid_bitmap(sbi);
>  
> -     build_free_nids(sbi, true, true);
> +     build_free_nids(sbi, true, true, FREE_HOT_NID);
> +     build_free_nids(sbi, true, true, FREE_COLD_NID);
>       return 0;
>  }
>  
> @@ -2794,21 +2865,26 @@ void destroy_node_manager(struct f2fs_sb_info *sbi)
>       struct nat_entry_set *setvec[SETVEC_SIZE];
>       nid_t nid = 0;
>       unsigned int found;
> +     enum nid_state state;
>  
>       if (!nm_i)
>               return;
>  
>       /* destroy free nid list */
>       spin_lock(&nm_i->nid_list_lock);
> -     list_for_each_entry_safe(i, next_i, &nm_i->free_nid_list, list) {
> -             __remove_free_nid(sbi, i, FREE_NID);
> -             spin_unlock(&nm_i->nid_list_lock);
> -             kmem_cache_free(free_nid_slab, i);
> -             spin_lock(&nm_i->nid_list_lock);
> +     for (state = FREE_HOT_NID; state < MAX_NID_TYPE; state++) {
> +             list_for_each_entry_safe(i, next_i,
> +                             &nm_i->free_nid_list[state], list) {
> +                     __remove_free_nid(sbi, i, state);
> +                     spin_unlock(&nm_i->nid_list_lock);
> +                     kmem_cache_free(free_nid_slab, i);
> +                     spin_lock(&nm_i->nid_list_lock);
> +             }
> +             f2fs_bug_on(sbi, nm_i->nid_cnt[state]);
> +             f2fs_bug_on(sbi, !list_empty(&nm_i->free_nid_list[state]));
>       }
> -     f2fs_bug_on(sbi, nm_i->nid_cnt[FREE_NID]);
> +
>       f2fs_bug_on(sbi, nm_i->nid_cnt[PREALLOC_NID]);
> -     f2fs_bug_on(sbi, !list_empty(&nm_i->free_nid_list));
>       spin_unlock(&nm_i->nid_list_lock);
>  
>       /* destroy nat cache */
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index 2129d63ab3d7..732c8e672fe2 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -157,24 +157,9 @@ struct nat_entry_set {
>  struct free_nid {
>       struct list_head list;  /* for free node id list */
>       nid_t nid;              /* node id */
> -     int state;              /* in use or not: FREE_NID or PREALLOC_NID */
> +     int state;              /* in use or not */
>  };
>  
> -static inline void next_free_nid(struct f2fs_sb_info *sbi, nid_t *nid)
> -{
> -     struct f2fs_nm_info *nm_i = NM_I(sbi);
> -     struct free_nid *fnid;
> -
> -     spin_lock(&nm_i->nid_list_lock);
> -     if (nm_i->nid_cnt[FREE_NID] <= 0) {
> -             spin_unlock(&nm_i->nid_list_lock);
> -             return;
> -     }
> -     fnid = list_first_entry(&nm_i->free_nid_list, struct free_nid, list);
> -     *nid = fnid->nid;
> -     spin_unlock(&nm_i->nid_list_lock);
> -}
> -
>  /*
>   * inline functions
>   */
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 720b01461adc..2ffb5c2d205e 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -487,10 +487,12 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
>       if (!available_free_memory(sbi, NAT_ENTRIES))
>               try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK);
>  
> -     if (!available_free_memory(sbi, FREE_NIDS))
> +     if (!available_free_memory(sbi, FREE_NIDS)) {
>               try_to_free_nids(sbi, MAX_FREE_NIDS);
> -     else
> -             build_free_nids(sbi, false, false);
> +     } else {
> +             build_free_nids(sbi, false, false, FREE_HOT_NID);
> +             build_free_nids(sbi, false, false, FREE_COLD_NID);
> +     }
>  
>       if (!is_idle(sbi) && !excess_dirty_nats(sbi))
>               return;
> diff --git a/fs/f2fs/shrinker.c b/fs/f2fs/shrinker.c
> index 0b5664a1a6cc..7b35746fb615 100644
> --- a/fs/f2fs/shrinker.c
> +++ b/fs/f2fs/shrinker.c
> @@ -28,7 +28,8 @@ static unsigned long __count_nat_entries(struct 
> f2fs_sb_info *sbi)
>  
>  static unsigned long __count_free_nids(struct f2fs_sb_info *sbi)
>  {
> -     long count = NM_I(sbi)->nid_cnt[FREE_NID] - MAX_FREE_NIDS;
> +     long count = NM_I(sbi)->nid_cnt[FREE_HOT_NID] +
> +                     NM_I(sbi)->nid_cnt[FREE_COLD_NID] - MAX_FREE_NIDS;
>  
>       return count > 0 ? count : 0;
>  }
> diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> index ae2dfa709f5d..c42a670e17f6 100644
> --- a/fs/f2fs/xattr.c
> +++ b/fs/f2fs/xattr.c
> @@ -397,7 +397,7 @@ static inline int write_all_xattrs(struct inode *inode, 
> __u32 hsize,
>       int err = 0;
>  
>       if (hsize > inline_size && !F2FS_I(inode)->i_xattr_nid)
> -             if (!alloc_nid(sbi, &new_nid))
> +             if (!alloc_nid(sbi, &new_nid, FREE_COLD_NID))
>                       return -ENOSPC;
>  
>       /* write to inline xattr */
> @@ -407,7 +407,7 @@ static inline int write_all_xattrs(struct inode *inode, 
> __u32 hsize,
>               } else {
>                       in_page = get_node_page(sbi, inode->i_ino);
>                       if (IS_ERR(in_page)) {
> -                             alloc_nid_failed(sbi, new_nid);
> +                             alloc_nid_failed(sbi, new_nid, FREE_COLD_NID);
>                               return PTR_ERR(in_page);
>                       }
>                       inline_addr = inline_xattr_addr(inode, in_page);
> @@ -418,7 +418,7 @@ static inline int write_all_xattrs(struct inode *inode, 
> __u32 hsize,
>               /* no need to use xattr node block */
>               if (hsize <= inline_size) {
>                       err = truncate_xattr_node(inode);
> -                     alloc_nid_failed(sbi, new_nid);
> +                     alloc_nid_failed(sbi, new_nid, FREE_COLD_NID);
>                       if (err) {
>                               f2fs_put_page(in_page, 1);
>                               return err;
> @@ -434,7 +434,7 @@ static inline int write_all_xattrs(struct inode *inode, 
> __u32 hsize,
>               xpage = get_node_page(sbi, F2FS_I(inode)->i_xattr_nid);
>               if (IS_ERR(xpage)) {
>                       err = PTR_ERR(xpage);
> -                     alloc_nid_failed(sbi, new_nid);
> +                     alloc_nid_failed(sbi, new_nid, FREE_COLD_NID);
>                       goto in_page_out;
>               }
>               f2fs_bug_on(sbi, new_nid);
> @@ -445,7 +445,7 @@ static inline int write_all_xattrs(struct inode *inode, 
> __u32 hsize,
>               xpage = new_node_page(&dn, XATTR_NODE_OFFSET);
>               if (IS_ERR(xpage)) {
>                       err = PTR_ERR(xpage);
> -                     alloc_nid_failed(sbi, new_nid);
> +                     alloc_nid_failed(sbi, new_nid, FREE_COLD_NID);
>                       goto in_page_out;
>               }
>               alloc_nid_done(sbi, new_nid);
> -- 
> 2.15.0.55.gc2ece9dc4de6

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