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Date: Thu, 12 Mar 2009 23:29:04 +0530
From: Sandeep K Sinha <sandeepksinha@...il.com>
To: Greg Freemyer <greg.freemyer@...il.com>
Cc: ext4 <linux-ext4@...r.kernel.org>,
Kernel Newbies <kernelnewbies@...linux.org>,
Manish Katiyar <mkatiyar@...il.com>
Subject: Re: [ext2/ext3] Re-allocation of blocks for an inode
On Thu, Mar 12, 2009 at 9:43 PM, Greg Freemyer <greg.freemyer@...il.com> wrote:
> On Thu, Mar 12, 2009 at 11:16 AM, Sandeep K Sinha
> <sandeepksinha@...il.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.
>
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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