[Ocfs2-devel] [PATCH 1/1] Ocfs2: Optimize punching-hole codes v3.

[Tao Ma <tao.ma@oracle.com>]

Hi Tristan,
	here comes the review.

Tristan Ye wrote:
> Changes from v2 to v3:
> 
<snip>
> +/*
> + * Hepler to find the rightmost record which contains 'pos' cpos,
> + * skip the holes if any, also adjust the 'pos' accordingly.
You don't mentioned what 'pos' indicates here, so it is very hard to 
read this function and I have to guess. ;) So please describe it in detail.
> + */
> +static void ocfs2_find_rec_with_pos(struct ocfs2_extent_list *el,
> +				    struct ocfs2_extent_rec **rec_got,
> +				    u32 *pos)
> +{
> +	int i;
> +	u32 range;
> +	struct ocfs2_extent_rec *rec = NULL;
> +
> +	for (i = le16_to_cpu(el->l_next_free_rec) - 1; i >= 0; i--) {
> +
> +		rec = &el->l_recs[i];
> +		range = le32_to_cpu(rec->e_cpos) +
> +				ocfs2_rec_clusters(el, rec);
> +
> +		if (le32_to_cpu(rec->e_cpos) < *pos) {
> +			/*
> +			 * Skip a hole.
> +			 */
> +			if (range < *pos)
> +				*pos = range;
> +
> +			break;
> +		}
> +
> +		/*
> +		 * Simply jump to previous record if the pos is
> +		 * the start of a record.
> +		 */
> +		if (le32_to_cpu(rec->e_cpos) == *pos) {
> +			i--;
> +			if (i < 0) {
> +				*rec_got = NULL;
> +				return;
> +			}
> +
> +			rec = &el->l_recs[i];
> +			range = le32_to_cpu(rec->e_cpos) +
> +					ocfs2_rec_clusters(el, rec);
> +			/*
> +			 * Skip a hole.
> +			 */
> +			if (range < *pos)
> +				*pos = range;
do we still need to check range < *pos? As you have already check
le32_to_cpu(rec->e_cpos) == *pos.
> +
> +			break;
> +		}
> +	}
> +
> +	*rec_got = &el->l_recs[i];
> +}
> +
> +/*
> + * Helper to calculate the punching pos and length in one run, we handle the
> + * following three cases in order:
> + *
> + * - remove the entire record
> + * - remove a partial record
> + * - no record needs to be removed (hole-punching completed)
> +*/
> +static void ocfs2_calc_trunc_pos(struct inode *inode,
> +				 struct ocfs2_extent_list *el,
> +				 struct ocfs2_extent_rec *rec,
> +				 u32 trunc_start, u32 *trunc_cpos,
> +				 u32 *trunc_len, u32 *trunc_end,
> +				 u64 *blkno, int *done)
> +{
> +	int ret = 0;
> +	u32 coff, range;
> +
> +	range = le32_to_cpu(rec->e_cpos) + ocfs2_rec_clusters(el, rec);
> +
> +	if (le32_to_cpu(rec->e_cpos) >= trunc_start) {
> +		*trunc_cpos = le32_to_cpu(rec->e_cpos);
> +		*trunc_len = *trunc_end - le32_to_cpu(rec->e_cpos);
> +		*blkno = le64_to_cpu(rec->e_blkno);
> +		*trunc_end = le32_to_cpu(rec->e_cpos);
> +	} else if (range > trunc_start) {
> +		*trunc_cpos = trunc_start;
> +		*trunc_len = range - trunc_start;
> +		coff = trunc_start - le32_to_cpu(rec->e_cpos);
> +		*blkno = le64_to_cpu(rec->e_blkno) +
> +				ocfs2_clusters_to_blocks(inode->i_sb, coff);
> +		*trunc_end = trunc_start;
> +	} else {
> +		/*
> +		 * It may have two following possibilities:
> +		 *
> +		 * - last record has been removed
what do you mean last record here? Sorry, I don't understand this case.
> +		 * - trunc_start was within a hole
> +		 *
> +		 * both two cases mean the completion of hole punching.
> +		 */
> +		ret = 1;
> +	}
> +
> +	*done = ret;
> +}
> +
>  static int ocfs2_remove_inode_range(struct inode *inode,
>  				    struct buffer_head *di_bh, u64 byte_start,
>  				    u64 byte_len)
>  {
> -	int ret = 0, flags = 0;
> -	u32 trunc_start, trunc_len, cpos, phys_cpos, alloc_size;
> +	int ret = 0, flags = 0, done = 0;
> +	u32 trunc_start, trunc_len, trunc_end, trunc_cpos, phys_cpos;
> +	u32 cluster_within_list;
>  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>  	struct ocfs2_cached_dealloc_ctxt dealloc;
>  	struct address_space *mapping = inode->i_mapping;
>  	struct ocfs2_extent_tree et;
> +	struct ocfs2_path *path = NULL;
> +	struct ocfs2_extent_list *el = NULL;
> +	struct ocfs2_extent_rec *rec = NULL;
>  	struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;
> -	u64 refcount_loc = le64_to_cpu(di->i_refcount_loc);
> +	u64 blkno, refcount_loc = le64_to_cpu(di->i_refcount_loc);
>  
>  	ocfs2_init_dinode_extent_tree(&et, INODE_CACHE(inode), di_bh);
>  	ocfs2_init_dealloc_ctxt(&dealloc);
> @@ -1482,16 +1588,13 @@ static int ocfs2_remove_inode_range(struct inode *inode,
>  	}
>  
>  	trunc_start = ocfs2_clusters_for_bytes(osb->sb, byte_start);
> -	trunc_len = (byte_start + byte_len) >> osb->s_clustersize_bits;
> -	if (trunc_len >= trunc_start)
> -		trunc_len -= trunc_start;
> -	else
> -		trunc_len = 0;
> +	trunc_end = (byte_start + byte_len) >> osb->s_clustersize_bits;
> +	cluster_within_list = trunc_end;
You said in the comments below that "we want to find a path which 
contains (trunc_end - 1)". So we also need to set trunc_end -1 here? 
Otherwise you may enter the wrong extent block in some case?
>  
> -	mlog(0, "Inode: %llu, start: %llu, len: %llu, cstart: %u, clen: %u\n",
> +	mlog(0, "Inode: %llu, start: %llu, len: %llu, cstart: %u, cend: %u\n",
>  	     (unsigned long long)OCFS2_I(inode)->ip_blkno,
>  	     (unsigned long long)byte_start,
> -	     (unsigned long long)byte_len, trunc_start, trunc_len);
> +	     (unsigned long long)byte_len, trunc_start, trunc_end);
>  
>  	ret = ocfs2_zero_partial_clusters(inode, byte_start, byte_len);
>  	if (ret) {
> @@ -1499,32 +1602,65 @@ static int ocfs2_remove_inode_range(struct inode *inode,
>  		goto out;
>  	}
>  
> -	cpos = trunc_start;
> -	while (trunc_len) {
> -		ret = ocfs2_get_clusters(inode, cpos, &phys_cpos,
> -					 &alloc_size, &flags);
> +	path = ocfs2_new_path_from_et(&et);
> +	if (!path) {
> +		ret = -ENOMEM;
> +		mlog_errno(ret);
> +		goto out;
> +	}
> +
> +	while (trunc_end > 0) {
I am just curious of this check. trunc_end seems to be a cluster offset. 
So how could it be 0 in case we don't punch from the 0 and where do you 
set it to 0?
> +		/*
> +		 * Unlike truncate codes, here we want to find a path which
> +		 * contains (trunc_end - 1) cpos, and then trunc_end will be
> +		 * decreased after each removal of a record range.
> +		 *
> +		 * Why not using trunc_end to search the path?
> +		 * The reason is simple, think about the situation of crossing
> +		 * the extent block, we need to find the adjacent block by
> +		 * decreasing one cluster, otherwise, it will run into a loop.
> +		 */
> +		ret = ocfs2_find_path(INODE_CACHE(inode), path,
> +				      cluster_within_list);
>  		if (ret) {
>  			mlog_errno(ret);
>  			goto out;
>  		}
>  
> -		if (alloc_size > trunc_len)
> -			alloc_size = trunc_len;
> +		el = path_leaf_el(path);
>  
> -		/* Only do work for non-holes */
> -		if (phys_cpos != 0) {
> -			ret = ocfs2_remove_btree_range(inode, &et, cpos,
> -						       phys_cpos, alloc_size,
> -						       &dealloc, refcount_loc,
> -						       flags);
> -			if (ret) {
> -				mlog_errno(ret);
> -				goto out;
> -			}
> +		ocfs2_find_rec_with_pos(el, &rec, &trunc_end);
> +		/*
> +		 * Go to next extent block directly when last rec was truncated.
> +		 */
> +		if (!rec) {
> +			cluster_within_list = trunc_end - 1;
> +			ocfs2_reinit_path(path, 1);
> +			break;
ocfs2_find_rec_with_pos will find a rec contains trunc_end and if there 
is no such rec and trunc_end < el->l_recs[0].e_cpos, rec will be set 
NULL, right?
So what if the el is in the left most extent block? Your function will 
iterate again and again with every time trunc_end--?
another problem is that your comments is "Go to next extent block 
directly when last rec was truncated", I guess you mean 'previous'? And 
  you 'break' here, so how could the previous extent block get punched? 
Am I wrong somehow?
>  		}
>  
> -		cpos += alloc_size;
> -		trunc_len -= alloc_size;
> +		ocfs2_calc_trunc_pos(inode, el, rec, trunc_start, &trunc_cpos,
> +				     &trunc_len, &trunc_end, &blkno, &done);
> +		if (done)
> +			break;
> +
> +		flags = rec->e_flags;
> +		phys_cpos = ocfs2_blocks_to_clusters(inode->i_sb, blkno);
> +
> +		ret = ocfs2_remove_btree_range(inode, &et, trunc_cpos,
> +					       phys_cpos, trunc_len, &dealloc,
> +					       refcount_loc, flags);
> +		if (ret < 0) {
> +			mlog_errno(ret);
> +			goto out;
> +		}
> +
> +		if (trunc_end > 0)
> +			cluster_within_list = trunc_end - 1;
> +		else
> +			break;
> +
> +		ocfs2_reinit_path(path, 1);
>  	}
>  
>  	ocfs2_truncate_cluster_pages(inode, byte_start, byte_len);

Regards,
Tao