[Ocfs2-devel] [RFC] ocfs2: Make ocfs2_extend_trans really extending.

[Tao Ma <tao.ma@oracle.com>]

Hi Mark,
Mark Fasheh wrote:
> On Mon, Mar 22, 2010 at 04:01:44PM +0800, Tao Ma wrote:
>   
>> Hi Joel/Mark/Sunil,
>> 	This patch just want to make ocfs2_extend_trans(which used
>> to restart the journal with only 'nblocks' in some case) really
>> extending. I have met with many troubles when I used this function
>> in implementing xattr support. And I used to think that it is
>> my fault.
>>
>> But I changed my mind when I saw that Joel(Sorry, Joel, ;) ) also use
>> it wrongly. See
>> http://git.kernel.org/?p=linux/kernel/git/jlbec/ocfs2.git;a=commitdiff;h=991f171d287781ae12d1ec06cb1917dae3334a9b;hp=f5abd5404e8d1551f1bf58b711543e3b5dcc1079
>>
>> Acutally ocfs2_extend_trans in ocfs2_block_group_alloc_discontig
>> has to be
>> 	status = ocfs2_extend_trans(handle,
>> 				    ocfs2_calc_bg_discontig_credits(osb->sb) +
>> 				    handle->h_buffer_credits);
>> because we will modify the bitmap file later which isn't included in
>> ocfs2_calc_bg_discontig_credits.
>>
>> That makes me to think more. So why we don't reserve the old blocks? I just
>> skimmed all the callers of ocfs2_extend_trans, and to my surprise, 12 of 15
>> callers added h_buffer_credits by themself to avoid the problem. Then why
>> handle this in ocfs2_extend_trans? So here comes the patch. Please review.
>>     
>
> Tao, this patch looks good to me. Thank you for taking on the time to fix up
> this old interface. Have you tested the patch much? What are the results
> like? Not only in stability, but does the new math inside
> ocfs2_extend_trans() speed up any long-running operations?
>   
I only did tristan's reflink test cases. And since it is only a RFC, I 
haven't put much time on it.
If you and Joel are both fine with it, I will give it more try, 
especially the stress test case on xattr, since it depends on
it heavily. And also I will run some fill_verify_hole test which will 
stress our b-tree codes.
I think these 2 places may be impacted most by this patch.

Regards,
Tao