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Date: Thu, 12 Mar 2009 14:37:17 -0400
From: Greg Freemyer <greg.freemyer@...il.com>
To: Sandeep K Sinha <sandeepksinha@...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 1:59 PM, Sandeep K Sinha
<sandeepksinha@...il.com> wrote:
> 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.
Sandeep,
As I read that bug report, the issue would be resolved by doing:
truncate(a)
fsync(a)
allocate_additional_blocks_for_b()
fsync(b)
But for the reporter the issue is that the code manipulating file A is
independent of the code manipulating file B thus it needs to be fixed
in a different way.
Since you have total control of both the files (inodes & data blocks)
in question, you should be able to find a better way than calling
sync_dirty_buffer() for every block you copy.
Have you actually seen data corruption if you leave out the
sync_dirty_buffer() call, or is it a theoretical issue?
Have you tried calling ext2_sync_inode() at the end of the copy loop
instead of sync_dirty_buffer() on every iteration. I really can't see
why that would be any more dangerous. Yet it would at least allow the
elevators and caches to work for an entire file at a time.
Greg
>> 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.”
>
--
Greg Freemyer
Head of EDD Tape Extraction and Processing team
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
--
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