[Ocfs2-devel] [PATCH 1/1] Ocfs2: Optimize punching-hole codes v2.

[Joel Becker]

On Thu, Feb 25, 2010 at 05:49:08PM +0800, Tristan Ye wrote:
> ===========================================================================
>  * Former punching-hole mechanism:
> ===========================================================================
> 
>    I waited 1 hour for its completion, unfortunately it's still ongoing.
> 
> ===========================================================================
>  * Patched punching-hode mechanism:
> ===========================================================================
> 
>    real	0m2.518s
>    user	0m0.000s
>    sys	0m2.445s
> 
> That means we've gained up to 1000 times improvement on performance in this
> case, whee! It's fairly cool. and it looks like that performance gain will
> be raising when extent records grow.

	Love the numbers, obviously.

> The patch was based on my former 2 patches, which were about truncating
> codes optimization and fixup to handle CoW on punching hole.

	I've already reviewed these.  I'm waiting on Mark's ack for them
to go to ocfs2.git.

> -	cpos = trunc_start;
> -	while (trunc_len) {
> -		ret = ocfs2_get_clusters(inode, cpos, &phys_cpos,
> -					 &alloc_size, &flags);
> -		if (ret) {
> -			mlog_errno(ret);
> -			goto out;
> -		}
> +	path = ocfs2_new_path_from_et(&et);
> +	if (!path) {
> +		ret = -ENOMEM;
> +		mlog_errno(ret);
> +		goto out;
> +	}
> +
> +start:
> +	if (trunc_end == 0) {
> +		ret = 0;
> +		goto out;
> +	}

	NO!  Don't do loops via goto.  Just Don't.  There are some
convoluted functions that end up being cleaner with gotos, but they are
*convoluted*.  This is a simple loop.  Keep it that way.
	In fact, this all really wants to be a helper function:

	while (trunc_end > 0) {
		do_one_hunk();
		ocfs2_reinit_path(path, 1);
	}

	Actually, looking at the rest of the code, I see a couple
helpers.  If you wrap trunc_start, trunc_len, etc in a structure, you
can pass it through.

>  
> -		if (alloc_size > trunc_len)
> -			alloc_size = trunc_len;
> +	/*
> +	 * Unlike truncating codes, here we want to find a path which contains
> +	 * (trunc_end - 1) cpos, and trunc_end will be decreased after each
> +	 * removal of a record range.
> +	 *
> +	 * Why didn't use trunc_end to search the path?
> +	 * The reason is simple, think about the situation when we cross the
> +	 * extent block, we need to find the adjacent block by decreasing one
> +	 * cluster, otherwise, it will run into loop.
> +	 */
> +	ret = ocfs2_find_path(INODE_CACHE(inode), path, cluster_within_list);
> +	if (ret) {
> +		mlog_errno(ret);
> +		goto out;
> +	}
>  
> -		/* 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;
> -			}
> +	el = path_leaf_el(path);
> +
> +	for (i = le16_to_cpu(el->l_next_free_rec) - 1; i >= 0; i--) {
> +		rec = &el->l_recs[i];
> +		/*
> +		 * Find the rightmost record which contains 'trunc_end' cpos,
> +		 * and we just simply jump to previous record if the trunc_end
> +		 * is the start of a record.
> +		 */
> +		if (le32_to_cpu(rec->e_cpos) < trunc_end) {
> +			/*
> +			 * Skip a hole.
> +			 */
> +			if ((le32_to_cpu(rec->e_cpos) +
> +			     ocfs2_rec_clusters(el, rec)) < trunc_end)
> +				trunc_end = le32_to_cpu(rec->e_cpos) +
> +					ocfs2_rec_clusters(el, rec);
> +			break;
>  		}
>  
> -		cpos += alloc_size;
> -		trunc_len -= alloc_size;
> +		if (le32_to_cpu(rec->e_cpos) == trunc_end) {
> +			i--;
> +			break;
> +		}
> +	}
> +
> +	rec = &el->l_recs[i];

	This is the first helper.  It finds the rec.

> +	flags = rec->e_flags;
> +	range = le32_to_cpu(rec->e_cpos) + ocfs2_rec_clusters(el, rec);
> +
> +	/*
> +	 * Similar with the truncating codes, we also handle the
> +	 * following three cases in order:
> +	 *
> +	 * - remove the entire record
> +	 * - remove a partial record
> +	 * - no record needs to be removed
> +	 */
> +	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
> +		 * - trunc_start was within a hole
> +		 *
> +		 * both two cases mean the completion of hole punching.
> +		 */
> +		ret = 0;
> +		goto out;
>  	}
>  
> +	phys_cpos = ocfs2_blocks_to_clusters(inode->i_sb, blkno);

	This is the second helper.  It computes the actual results from
the found record.

> +	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;

	This is the third helper.  It does the actual punch.

Joel

-- 

"There are only two ways to live your life. One is as though nothing
 is a miracle. The other is as though everything is a miracle."
        - Albert Einstein

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127