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

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On Thu, Mar 12, 2009 at 9:43 PM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote:
> On Thu, Mar 12, 2009 at 11:16 AM, Sandeep K Sinha
> <sandeepksinha@xxxxxxxxx> 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.
>

probably the reason being that the ext2 has some issues with sync.
http://kerneltrap.org/index.php?q=mailarchive/linux-fsdevel/2007/2/14/316836/thread

Hence, if we don't do this we see a difference in the original and
reallocated file.



> 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
> First 99 Days Litigation White Paper -
> http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf
>
> The Norcross Group
> The Intersection of Evidence & Technology
> http://www.norcrossgroup.com
>



-- 
Regards,
Sandeep.





 	
“To learn is to change. Education is a process that changes the learner.”
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