linux-ext4 - Re: Why max_debt isn't used in ext4's find_group

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Date:	Thu, 19 Jul 2007 20:28:20 +0530
From:	Kalpak Shah <kalpak@...sterfs.com>
To:	Yan Zheng <ukernel@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Why max_debt isn't used in ext4's find_group_orlov(...) ?

On Thu, 2007-07-19 at 21:00 +0800, Yan Zheng wrote:
> Hi all
> 
> max_debt is used in ext2's find_group_orlov .  In ext4's
> find_group_orlov, max_debt is only computed, but not used.  I wonder
> whether it's a typo,  Can anyone give me a answer? The kernel source I
> read is 2.6.22.

I think you are right, max_debt is currently unused in the current
ext3/4 code. In ext2 max_debt is used along with s_debts (in struct
ext2_sb_info) to decide inode allocations. s_debts is no longer present
in ext3/4. 

You can find the reason for removing s_debts here:
http://osdir.com/ml/file-systems.ext2.devel/2004-09/msg00027.html

Basically use of s_debts was unsafe since it performed unlocked byte
increment/decrement on words which may be being accessed simultaneously
on other CPUs and since it was a dynamic in-memory table, it required
extension during online resize which needed proper locking.

Until s_debts is added again, I think the code relating to max_debts
should be removed?

Thanks,
Kalpak.

> 
> Thanks in advance.
> 
> ----------------
> Best Regards
> 
> YZ
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