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

[Jaegeuk Kim <jaegeuk@kernel.org>]

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@huawei.com>
> > ---
> >  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?

> 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);
> >