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

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Date:	Mon, 5 Dec 2011 18:55:46 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Lukas Czerner <lczerner@...hat.com>, tytso@....edu, tm@....ma,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Set the initial TRIM information as TRIMMED

On 12/3/11, Eric Sandeen <sandeen@...hat.com> wrote:
> On 12/1/11 6:01 PM, Kyungmin Park wrote:
>> On 12/2/11, Eric Sandeen <sandeen@...hat.com> wrote:
>>> On 12/1/11 1:00 AM, 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.
>>>>
>>>> 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);
>>>
>> Hi,
>>
>>> Hm, so if there were freed but un-trimmed blocks at this point, we will
>>> never trim them until we free _another_ block in the group, right?  That
>>> might be a reasonable tradeoff, but it is somewhat surprising behavior.
>>>
>>> i.e. say we do:
>>>
>>> mount /mnt
>>> rm -rf /mnt/very_big_file
>>> umount /mnt
>>>
>>> mount /mnt
>>> fitrim /mnt
>> another word, you can run fitrim after rm -rf
>> yes, it's trade-off.
>>
>> In my case, phone scenario, no umount system and data partition. it's
>> burden to trim at boot time. it has still slower boot time.
>> some daemon or program run fitrm at filesystem. it consumes time and
>> hurt other boot processes.
>>>
>>> then we won't trim anything at all, right, despite there being many
>>> new free blocks?  Which would be rather unexpected.
>>>
>>> If we don't store the trimmed state on disk, I think we should
>>> probably stick with the slower first-time trim, and the more obvious
>>> behavior (all free blocks are always trimmed whenever a trim
>>> command is issued).
>>
>> Umm how do you think, introduce the trim force command for this?
>
> Alternately, can we use a bit in bg_flags to keep a better view of this
> state on disk, if this is critical?

BTW, bg_flags in struct ext4_group_desc is same as ext4_group_info's bb_state?

Thank you,
Kyungmin Park
>
> -Eric
>
>> Thank you,
>> Kyungmin Park
>
>
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