[Ocfs2-devel] [PATCH 1/4] Ocfs2: Optimize truncting codes for ocfs2 to use ocfs2_remove_btree_range instead.

[tristan]

Hi Mark,

Thanks for the review:-)


Mark Fasheh wrote:
> On Tue, May 11, 2010 at 05:54:42PM +0800, Tristan Ye wrote:
>> As we known, truncate is just a special case of punching holes(from new i_size
>> to end), we therefore could take advantage of existing ocfs2_remove_btree_range()
>> codes to reduce the comlexity and redundancy in alloc.c, the goal here is to make
>> truncate codes more generic and straightforward.
>>
>> Several former functions only used by ocfs2_commit_truncate() will be simply wiped off.
>>
>> ocfs2_remove_btree_range() was originally used by punching holes codes, which didn't
>> take refcount into account(definitely it's a BUG), we therefore need to change that
>> func a bit to handle refcount treee lock, calculate and reserve block for refcount
>> tree changes, also decrease refcount at the end, to move these logics in, we needs
>> to replace the ocfs2_lock_allocators() by adding a new func ocfs2_reserve_blocks_for_rec_trunc()
>> which accepts some extra blocks to reserve. such changes will not hurt any other codes
>> who're using ocfs2_remove_btree_range(such as dir truncate and punching holes), actually
>> punching holes codes do benefit from this.
>>
>> I merge the following steps into one patch since they may be logically doing one thing,
>> Though I knew it looks a little bit fat to review.
>>
>> 1). Remove redundant codes used by ocfs2_commit_truncate before, since we're moving to
>>     ocfs2_remove_btree_range anyway.
>>
>> 2). Add a new func ocfs2_reserve_blocks_for_rec_trunc() for purpose of accepting  some
>>     extra blocks to reserve.
>>
>> 3). Change ocfs2_prepare_refcount_change_for_del() a bit to fit our needs, it's safe to
>>     do this since it's only being called by truncating codes.
>>
>> 4). Change ocfs2_remove_btree_range() a bit to take refcount case into account.
>>
>> 5). Finally, we change ocfs2_commit_truncate() to call ocfs2_remove_btree_range() in
>>     a proper way.
>>
>> The patch has been tested normally for sanity check, stress tests with heavier workload
>> will be expected.
>>
>> Based on this patch, our fixing to punching holes bug will be fairly easy.
>>
>> Signed-off-by: Tristan Ye <tristan.ye at oracle.com>
>> ---
>>  fs/ocfs2/alloc.c        |  685 +++++++++++------------------------------------
>
> Excellent - that's a lot of redundant code we get to remove  :) Thanks
> Tristan for taking this on!
>
>
>>  fs/ocfs2/alloc.h        |    8 +-
>>  fs/ocfs2/dir.c          |    4 +-
>>  fs/ocfs2/file.c         |   11 +-
>>  fs/ocfs2/inode.c        |    9 +-
>>  fs/ocfs2/refcounttree.c |   29 +--
>>  fs/ocfs2/refcounttree.h |    4 +-
>>  7 files changed, 178 insertions(+), 572 deletions(-)
>>
>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>> index 0cb2945..0cb4248 100644
>> --- a/fs/ocfs2/alloc.c
>> +++ b/fs/ocfs2/alloc.c
>> @@ -5587,19 +5587,97 @@ out:
>>  	return ret;
>>  }
>>  
>> +/*
>> + * ocfs2_reserve_blocks_for_rec_trunc() would look basically the
>> + * same as ocfs2_lock_alloctors(), except for it accepts a blocks
>> + * number to reserve some extra blocks, and it only handles meta
>> + * data allocations.
>> + *
>> + * Currently, only ocfs2_remove_btree_range() uses it for truncating
>> + * and punching holes.
>> + */
>> +static int ocfs2_reserve_blocks_for_rec_trunc(struct inode *inode,
>> +					      struct ocfs2_extent_tree *et,
>> +					      u32 extents_to_split,
>> +					      struct ocfs2_alloc_context **ac,
>> +					      int extra_blocks)
>> +{
>> +	int ret = 0, num_free_extents;
>> +	unsigned int max_recs_needed = 2 * extents_to_split;
>> +	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>> +
>> +	*ac = NULL;
>> +
>> +	num_free_extents = ocfs2_num_free_extents(osb, et);
>> +	if (num_free_extents < 0) {
>> +		ret = num_free_extents;
>> +		mlog_errno(ret);
>> +		goto out;
>> +	}
>> +
>> +	if (!num_free_extents ||
>> +	    (ocfs2_sparse_alloc(osb) && num_free_extents < max_recs_needed))
>> +		extra_blocks += ocfs2_extend_meta_needed(et->et_root_el);
>> +
>> +	if (extra_blocks) {
>> +		ret = ocfs2_reserve_new_metadata_blocks(osb, extra_blocks, ac);
>> +		if (ret < 0) {
>> +			if (ret != -ENOSPC)
>> +				mlog_errno(ret);
>
> This means we could possibly -ENOSPC while trying to truncate a reflinked
> file (to free space perhaps). This problem is out of the scope of your patch
> so I'm not asking you to fix it here, but it seems worth noting.

Look at former code piece:

/* Always lock for any unwritten extents - we might want to
* add blocks during a split.
*/
if (!num_free_extents ||
(ocfs2_sparse_alloc(osb) && num_free_extents < max_recs_needed)) {
ret = ocfs2_reserve_new_metadata(osb, et->et_root_el, meta_ac);
if (ret < 0) {
if (ret != -ENOSPC)
mlog_errno(ret);
goto out;
}
}

It also has the possibility to meet -ENOSPC.

Tao,

Do we really have to free space in that case when being failed to ask 
blocks for refcounting stuffs.

>
>
>
> Rest of the patch looks good. The testing results are promising too.
>
> Silly question - did you test that a 'punch hole' for the entire range of a
> file produces a result identical to that of truncating the file to zero size?

I've tested this for sure:-), they're totally the same except for 
punching-hole change
nothing on i_size.


>
>
> Acked-by: Mark Fasheh <mfasheh at suse.com>
> 	--Mark
>
> --
> Mark Fasheh