linux-ext4 - Re: [PATCH] Set the initial TRIM information as TRIMMED

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Date:	Thu, 01 Dec 2011 16:30:11 +0800
From:	Tao Ma <tm@....ma>
To:	Kyungmin Park <kmpark@...radead.org>
CC:	tytso@....edu, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Set the initial TRIM information as TRIMMED

On 12/01/2011 04:19 PM, Kyungmin Park wrote:
> On 12/1/11, Tao Ma <tm@....ma> wrote:
>> Hi Kyungmin,
>> On 12/01/2011 03:00 PM, Kyungmin Park wrote:
>>> From: Kyungmin Park <kyungmin.park@...sung.com>
>>>
>>> Now trim information doesn't stored at disk so every boot time. it's
>>> cleared.
>>> and do the trim all disk groups.
>>> But assume that it's already trimmed at previous time so don't need to
>>> trim it again. So set the intial state as trimmed.
>> sorry, I don't get your meaning here.
>> Why can we assume that the group is already trimmed since it isn't
>> stored in the disk?
> To avoid the first time trim operation.
> Every boot time. run the fitrim then it trims all block groups again.
> but it's already done at previous time. so don't need to trim it
> again.
> Doesn't make sense? I think it's not designed behavior.
You make the assumption that we run the fitrim every time at boot time.
But what if the user don't run it at all? I guess "run fitrim during
boot" is your firmware's behaviour and it isn't an assumption for all
the other users.

Having said that, this flag will be cleared whenever some
blocks/clusters are freed. So maybe it doesn't matter for setting this
flag during the group initialization.

Thanks
Tao
> 
> In your patch at http://patchwork.ozlabs.org/patch/102918/
> 
> with the patch:
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m5.625s
> user	0m0.000s
> sys	0m1.269s
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m0.002s
> user	0m0.000s
> sys	0m0.001s
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m0.002s
> user	0m0.000s
> sys	0m0.001s
> 
> After reboot. it maybe become below
> 
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m0.002s
> user	0m0.000s
> sys	0m0.001s
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m0.002s
> user	0m0.000s
> sys	0m0.001s
> [root@...u-tm linux-2.6]# time ./ftrim /mnt/ext4/a
> real	0m0.002s
> user	0m0.000s
> sys	0m0.001s
> 
> Thank you,
> Kyungmin Park
>>
>> Thanks
>> Tao
>>>
>>> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
>>> ---
>>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>>> index e2d8be8..97ef342 100644
>>> --- a/fs/ext4/mballoc.c
>>> +++ b/fs/ext4/mballoc.c
>>> @@ -1098,6 +1098,12 @@ int ext4_mb_init_group(struct super_block *sb,
>>> ext4_group_t group)
>>>  		goto err;
>>>  	}
>>>  	mark_page_accessed(page);
>>> +
>>> +	/*
>>> +	 * TRIM information is not stored at disk so set the initial
>>> +	 * state as trimmed. Since previous time it's already trimmed all
>>> +	 */
>>> +	EXT4_MB_GRP_SET_TRIMMED(this_grp);
>>>  err:
>>>  	ext4_mb_put_buddy_page_lock(&e4b);
>>>  	return ret;
>>
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