linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: optimize the way of traversing free_nid

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Date:   Wed, 8 Nov 2017 16:52:21 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Fan Li <fanofcode.li@...sung.com>, 'Chao Yu' <chao@...nel.org>,
        "'Jaegeuk Kim'" <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] f2fs: optimize the way of traversing
 free_nid_bitmap

On 2017/11/7 19:14, Fan Li wrote:
> We call scan_free_nid_bits only when there isn't many
> free nids left, it means that marked bits in free_nid_bitmap
> are supposed to be few, use find_next_bit_le is more
> efficient in such case.
> According to my tests, use find_next_bit_le instead of
> test_bit_le will cut down the traversal time to one
> third of its original.
> 
> Signed-off-by: Fan li <fanofcode.li@...sung.com>

Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks,

> ---
>  fs/f2fs/node.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index fef5c68..d234c6e 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1955,6 +1955,7 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>  	struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
>  	struct f2fs_journal *journal = curseg->journal;
>  	unsigned int i, idx;
> +	nid_t nid;
>  
>  	down_read(&nm_i->nat_tree_lock);
>  
> @@ -1964,10 +1965,10 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>  		if (!nm_i->free_nid_count[i])
>  			continue;
>  		for (idx = 0; idx < NAT_ENTRY_PER_BLOCK; idx++) {
> -			nid_t nid;
> -
> -			if (!test_bit_le(idx, nm_i->free_nid_bitmap[i]))
> -				continue;
> +			idx = find_next_bit_le(nm_i->free_nid_bitmap[i],
> +						NAT_ENTRY_PER_BLOCK, idx);
> +			if (idx >= NAT_ENTRY_PER_BLOCK)
> +				break;
>  
>  			nid = i * NAT_ENTRY_PER_BLOCK + idx;
>  			add_free_nid(sbi, nid, true);
> @@ -1980,7 +1981,6 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
>  	down_read(&curseg->journal_rwsem);
>  	for (i = 0; i < nats_in_cursum(journal); i++) {
>  		block_t addr;
> -		nid_t nid;
>  
>  		addr = le32_to_cpu(nat_in_journal(journal, i).block_addr);
>  		nid = le32_to_cpu(nid_in_journal(journal, i));
>