Re: [ext2/ext3] Re-allocation of blocks for an inode

[Greg Freemyer <greg.freemyer@gmail.com>]

On Thu, Mar 12, 2009 at 11:16 AM, Sandeep K Sinha
<sandeepksinha@gmail.com> wrote:
> Hi all,
>
> I am listing above two codes for re-allocating new blocks for a given inode.
>
> These code snippets are specific to  ext2.
> The problem here is that it is performing slower than cp and dd.
>
> Can anyone help in determining what can be the possible reason(s) ?

Excessive use of sync_dirty_buffer();

You're calling it for every single block you copy. Pretty sure it is a
very aggressive call that forces the data out to the disk immediately,
thus the benefits of caching and elevators are lost.  And those are
big benefits.

Greg


>
> 1. MEMCPY
> =======
>
>
>
>                src_ind = ext2_iget (sb, inum);
>        if (!src_ind) {
>                printk (KERN_DEBUG "\n OHSM Source Inode Not Found ");
>                goto out_err;
>        }
>
>        /* Getting the ghost inode */
>        dest_ind = ext2_new_inode (nd.path.dentry->d_inode, src_ind->i_mode);
>        if (IS_ERR(dest_ind)) {
>                printk (KERN_ALERT "\n OHSM destination inode unable to allocate.
> err = %ld", PTR_ERR(dest_ind));
>                goto out_err;
>        }
>
>        /* Locking the source inode using mutex */
>        mutex_lock (&src_ind->i_mutex);
>
>        /* Get the source inode size and number of blocks */
>        i_size = i_size_read(src_ind);
>
>        /* Calculating number of block to allocate for ghost inode */
>        nblocks = (i_size >> EXT2_BLOCK_SIZE_BITS(sb)) +
>                   ((i_size & (sb->s_blocksize - 1)) ? 1 : 0);
>
>        memset(&dest_bh, 0, sizeof(struct buffer_head));
>        memset(&src_bh, 0, sizeof(struct buffer_head));
>        for (done = 0; done < nblocks; done++) {
>
>             err = ext2_get_block (src_ind, done, &src_bh, 0);
>                if (err < 0) {
>                        printk (KERN_DEBUG "\n error getting blocks ret_val = %d",err);
>                        goto unlock;
>                }
>
>                dest_bh.b_state = 0;
>                err = ext2_get_block (dest_ind, done, &dest_bh, 1);
>                if (err < 0) {
>                        printk (KERN_DEBUG "\n error getting blocks ret_val = %d",err);
>                        goto unlock;
>                }
>
>                if (!buffer_mapped(&src_bh)){
>                        printk (KERN_DEBUG "\nHOLE ");
>                        continue;
>                }
>
>                src_bhptr = sb_bread(sb, src_bh.b_blocknr);
>                if (!src_bhptr)
>                        goto unlock;
>
>                dst_bhptr = sb_bread(sb, dest_bh.b_blocknr);
>                if (!dst_bhptr)
>                        goto unlock;
>
>                lock_buffer(dst_bhptr);
>                memcpy(dst_bhptr->b_data,src_bhptr->b_data,src_bhptr->b_size);
>                unlock_buffer(dst_bhptr);
>
>                mark_buffer_dirty(dst_bhptr);
>                sync_dirty_buffer(dst_bhptr);
>
>                brelse(src_bhptr);
>                brelse(dst_bhptr);
>
>        }
>
>        for (blk_index = 0; blk_index < 15; blk_index++) {
>                if (EXT2_I (dest_ind)->i_data[blk_index]){
>                        swap = EXT2_I (src_ind)->i_data[blk_index];
>                        EXT2_I (src_ind)->i_data[blk_index] =
>                                EXT2_I (dest_ind)->i_data[blk_index];
>                        EXT2_I (dest_ind)->i_data[blk_index] = swap;
>                }
>        }
>
>        dest_ind->i_blocks = src_ind->i_blocks ;
>        mark_inode_dirty (src_ind);
>        sync_mapping_buffers(src_ind->i_mapping);
>        ohsm_sync_inode(src_ind);
>        iput(src_ind);
>
>        dest_ind->i_nlink = 0;
>        iput(dest_ind);
>        mutex_unlock (&src_ind->i_mutex);
>        goto out_err;
>
> unlock:
>        brelse(src_bhptr);
>        brelse(dst_bhptr);
>        mutex_unlock (&src_ind->i_mutex);
>
> out_err:
>        path_put (&nd.path);
>        return;
>
>
>
> 2. PAGEFLIP
> ========
>
>
> /* Get the source inode */
>
>        src_ind = ext2_iget (sb, inum);
>        if (!src_ind) {
>                printk (KERN_DEBUG "\n OHSM Source Inode Not Found ");
>                goto out_err;
>        }
>
>        /* Getting the ghost inode */
>        dest_ind = ext2_new_inode (nd.path.dentry->d_inode, src_ind->i_mode);
>        if (IS_ERR(dest_ind)) {
>                printk (KERN_ALERT "\n destination inode unable to allocate. err =
> %ld", PTR_ERR(dest_ind));
>                goto out_err;
>        }
>
>        /* Locking the source inode using mutex */
>        mutex_lock (&src_ind->i_mutex);
>
>        /* Get the source inode size and number of blocks */
>        i_size = i_size_read(src_ind);
>
>        /* Calculating number of block to allocate for ghost inode */
>        nblocks = (i_size >> EXT2_BLOCK_SIZE_BITS(sb)) +
>                   ((i_size & (sb->s_blocksize - 1)) ? 1 : 0);
>
>
>        memset(&dest_bh, 0, sizeof(struct buffer_head));
>        memset(&src_bh, 0, sizeof(struct buffer_head));
>        for (done = 0; done < nblocks; done++) {
>
>             err = ext2_get_block (src_ind, done, &src_bh, 0);
>                if (err < 0) {
>                        printk (KERN_DEBUG "\n error getting blocks ret_val = %d",err);
>                        goto unlock;
>                }
>
>                dest_bh.b_state = 0;
>                err = ext2_get_block (dest_ind, done, &dest_bh, 1);
>                if (err < 0) {
>                        printk (KERN_DEBUG "\n error getting blocks ret_val = %d",err);
>                        goto unlock;
>                }
>
>                if (!buffer_mapped(&src_bh)){
>                        printk (KERN_DEBUG "\nHOLE ");
>                        continue;
>                }
>
>                src_bhptr = sb_bread(sb, src_bh.b_blocknr);
>                if (!src_bhptr)
>                        goto unlock;
>
>                dst_bhptr = sb_bread(sb, dest_bh.b_blocknr);
>                if (!dst_bhptr)
>                        goto unlock;
>
>               lock_buffer(dst_bhptr);
>               oldpage = dst_bhptr->b_page;
>               olddata = dst_bhptr->b_data;
>               dst_bhptr->b_data = src_bhptr->b_data;
>               dst_bhptr->b_page = src_bhptr->b_page;
>               flush_dcache_page(dst_bhptr->b_page);
>               unlock_buffer(dst_bhptr);
>
>               mark_buffer_dirty(dst_bhptr);
>               sync_dirty_buffer(dst_bhptr);
>
>               if(buffer_uptodate(dst_bhptr)) {
>                dst_bhptr->b_page  = oldpage;
>                dst_bhptr->b_data = olddata;
>               }
>
>             brelse(src_bhptr);
>             brelse(dst_bhptr);
>        }
>
>        for (blk_index = 0; blk_index < 15; blk_index++) {
>                if (EXT2_I (dest_ind)->i_data[blk_index]){
>                        swap = EXT2_I (src_ind)->i_data[blk_index];
>                        EXT2_I (src_ind)->i_data[blk_index] =
>                                EXT2_I (dest_ind)->i_data[blk_index];
>                        EXT2_I (dest_ind)->i_data[blk_index] = swap;
>                }
>        }
>
>        dest_ind->i_blocks = src_ind->i_blocks ;
>        mark_inode_dirty (src_ind);
>        sync_mapping_buffers(src_ind->i_mapping);
>        ohsm_sync_inode(src_ind);
>        iput(src_ind);
>
>        dest_ind->i_nlink = 0;
>        iput(dest_ind);
>        mutex_unlock (&src_ind->i_mutex);
>        goto out_err;
>
> unlock:
>        brelse(src_bhptr);
>        brelse(dst_bhptr);
>        mutex_unlock (&src_ind->i_mutex);
>
> out_err:
>        path_put (&nd.path);
>        return;
> }
>
>
>
> --
> Regards,
> Sandeep.
>
>
>
>
>
>
> “To learn is to change. Education is a process that changes the learner.”
>



-- 
Greg Freemyer
Litigation Triage Solutions Specialist
http://www.linkedin.com/in/gregfreemyer
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