[Ocfs2-devel] [PATCH 2/2] Ocfs2: Add a new code 'OCFS2_INFO_FREEFRAG' for o2info ioctl.

[Joel Becker]

On Wed, Nov 03, 2010 at 07:02:06PM +0800, Tristan Ye wrote:
> This new code is a bit more complicated than former ones, the goal is to
> show user all statistics required to take a deep insight into filesystem
> on how the disk is being fragmentaed.
> 
> The goal is achieved by scaning global bitmap from (cluster)group to group
> to figure out following factors in the filesystem:
> 
> 	- How many free chunks in a fixed size as user requested.
> 	- How many real free chunks in all size.

	Let me see if I understand the above requirements.  In the same
call, you are going build a list of free chunk sizes.  Then you will
also count how many chunks of a user-specified size.  Why can't the user
just take the list and look at the size they want?  What do they get
from specifying a size to the ioctl(2)?

  
> +void ocfs2_info_update_ffg(struct ocfs2_info_freefrag *ffg, __u32 chunksize)
> +{
> +	int index;
> +
> +	index = __ilog2_u32(chunksize);
> +	if (index >= OCFS2_INFO_MAX_HIST)
> +		index = OCFS2_INFO_MAX_HIST - 1;
> +
> +	ffg->iff_ffs.ffs_fc_hist.fc_chunks[index]++;
> +	ffg->iff_ffs.ffs_fc_hist.fc_clusters[index] += chunksize;
> +
> +	if (chunksize > ffg->iff_ffs.ffs_max)
> +		ffg->iff_ffs.ffs_max = chunksize;
> +
> +	if (chunksize < ffg->iff_ffs.ffs_min)
> +		ffg->iff_ffs.ffs_min = chunksize;
> +
> +	ffg->iff_ffs.ffs_avg += chunksize;
> +	ffg->iff_ffs.ffs_free_chunks_real++;
> +}

	I'm sorry, but this is just unreadable.  I get that we can only
abbreviate 'free-frag-scan' so many ways, but there is no way people
will understand this.
	I don't think renaming helps too much.  These names are always
going to be bad.  I think we *can* reduce the long structure strings,
mostly with helper functions.
	For example, here we could have:

static void o2ffg_update_histogram(struct ocfs2_info_free_chunk_list *hist,
                                   unsigned int chunksize)
{
	int index;

	index = __ilog2_u32(chunksize);
	if (index >= OCFS2_INFO_MAX_HIST)
		index = OCFS2_INFO_MAX_HIST - 1;

	hist->fc_chunks[index]++;
	hist->fc_clusters[index] += chunksize;
}

static void ocfs2_info_update_ffg(struct ocfs2_info_freefrag *ffg,
                                  unsigned int chunksize)
{
	o2ffg_update_histogram(&ffg->iff_ffs.ffs_fc_hist, chunksize);

 	...
}

and so on.  Btw, the chunksize can be an unsigned int, as the calling
function uses that type and not the more specific __u32.

> +int ocfs2_info_freefrag_scan_bitmap(struct inode *gb_inode,
> +				    struct ocfs2_info_freefrag *ffg)
> +{
> +	__u32 chunks_in_group;
> +	int status = 0, unlock = 0, i;
> +
> +	struct buffer_head *bh = NULL;
> +	struct ocfs2_chain_list *cl = NULL;
> +	struct ocfs2_chain_rec *rec = NULL;
> +	struct ocfs2_dinode *gb_dinode = NULL;
> +
> +	mutex_lock(&gb_inode->i_mutex);
> +
> +	if (!(ffg->iff_req.ir_flags & OCFS2_INFO_FL_NON_COHERENT)) {
> +		status = ocfs2_inode_lock(gb_inode, &bh, 0);
> +		if (status < 0) {
> +			mlog_errno(status);
> +			goto bail;
> +		}
> +		unlock = 1;
> +	} else {
> +		status = ocfs2_read_inode_block(gb_inode, &bh);
> +		if (status < 0) {
> +			mlog_errno(status);
> +			goto bail;
> +		}
> +	}

	Same thoughts about ocfs2_ilookup() here.

Joel

-- 

Life's Little Instruction Book #347

	"Never waste the oppourtunity to tell someone you love them."

Joel Becker
Senior Development Manager
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127