linux-ext4 - Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure delete journal blocks

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Date:	Mon, 10 Oct 2011 16:36:25 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	Jonathan Corbet <corbet@....net>
CC:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure delete
 journal blocks

On 10/10/2011 01:00 PM, Jonathan Corbet wrote:
> On Fri,  7 Oct 2011 00:11:05 -0700
> Allison Henderson<achender@...ux.vnet.ibm.com>  wrote:
>
>> +	/*
>> +	 * If the journal block was not found in the list,
>> +	 * add a new pair to the list
>> +	 */
>> +	if (!b_pair) {
>> +		b_pair = kzalloc(sizeof(struct jbd2_blk_pair), GFP_NOFS);
>> +		if (!b_pair) {
>> +			spin_unlock(&journal->j_pair_lock);
>> +			return -ENOMEM;
>> +		}
>
> Here too...  that really needs to be GFP_ATOMIC.
>
> I'm wondering, though...it looks like, over a short period of time, you
> will create an unordered linked list containing one entry for every
> physical block in the journal.  You'll take a lock and search the whole
> list for every block that is committed.  Wouldn't it be better just to
> have an array indexed by the journal logical block offset?  Less memory,
> faster access...?  Or am I missing something fundamental here?
>
> Thanks,
>
> jon

Hi Jon,

I think that's a good suggestion. Initially I had made it a linked
list since most of the journals existing lists were implemented as
linked lists, but since this list ends up being a fixed size, an
array is a good optimization here. Thx!

Allison

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