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Date: Mon, 18 Dec 2017 16:28:27 +0900
From: Hyunchul Lee <hyc.lee@...il.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>,
Chao Yu <chao@...nel.org>
CC: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, kernel-team@....com,
linux-fsdevel@...r.kernel.org, Hyunchul Lee <cheol.lee@....com>
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: pass down write hints to block layer
for bufferd write
Hi Jaegeuk,
Agreed. If Chao agrees with this policy, I will implement it.
Thanks for the comment.
On 12/15/2017 11:06 AM, Jaegeuk Kim wrote:
> On 12/14, Hyunchul Lee wrote:
>> Hi Jaegeuk,
>>
>> I need your comment about the fs_iohint mount option.
>>
>> a) w/o fs_iohint, propagate user hints to low layer.
>> b) w/ fs_iohint, ignore user hints, and use hints which is generated
>> with F2FS.
>>
>> Chao suggests this option. because user hints are more accurate than
>> file system.
>>
>> This is resonable, But I have some concerns about this option.
>> The first thing is that blocks of a segments have different hints. This
>> could make GC less effective.
>> The second is that the separation between LIFE_MEDIUM and LIFE_LONG is
>> really needed. I think that difference between them is a little ambigous
>> for users, and LIFE_SHORT and LIFE_EXTREME is converted to different
>> hints by F2FS.
>
> I think what we really can do would assign many user hints to our 3 DATA
> logs likewise rw_hint_to_seg_type(), since it's just hints for user data.
> Then, we can decide how to keep that as much as possible, since we have
> another filesystem metadata such as meta and nodes. In addition, I don't
> think we have to keep the original user-hints which makes F2FS logs be
> messed up.
>
> With that mind, I can think of the below cases. Especially, if user wants
> to keep their io_hints, we'd better recommend to use direct_io w/o fs_iohints.
> In order to keep this policy, I think fs_iohints would be better to be a
> feature set by mkfs.f2fs and detected by sysfs entries for users.
>
> 1) w/ fs_iohints
>
> User F2FS Block
> -------------------------------------------------------------------
> Meta WRITE_LIFE_MEDIUM
> HOT_NODE WRITE_LIFE_NOTSET
> WARM_NODE -'
> COLD_NODE WRITE_LIFE_NONE
> ioctl(cold) COLD_DATA WRITE_LIFE_EXTREME
> extention list -' -'
> WRITE_LIFE_EXTREME -' -'
> WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
>
> -- buffered_io
> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_LONG
> WRITE_LIFE_NONE -' -'
> WRITE_LIFE_MEDIUM -' -'
> WRITE_LIFE_LONG -' -'
>
> -- direct_io (Not recommendable)
> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
> WRITE_LIFE_NONE -' WRITE_LIFE_NONE
> WRITE_LIFE_MEDIUM -' WRITE_LIFE_MEDIUM
> WRITE_LIFE_LONG -' WRITE_LIFE_LONG
>
> 2) w/o fs_iohints
>
> User F2FS Block
> -------------------------------------------------------------------
> Meta -
> HOT_NODE -
> WARM_NODE -
> COLD_NODE -
> ioctl(cold) COLD_DATA -
> extention list -' -
>
> -- buffered_io
> WRITE_LIFE_EXTREME COLD_DATA -
> WRITE_LIFE_SHORT HOT_DATA -
> WRITE_LIFE_NOT_SET WARM_DATA -
> WRITE_LIFE_NONE -' -
> WRITE_LIFE_MEDIUM -' -
> WRITE_LIFE_LONG -' -
>
> -- direct_io
> WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
> WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
> WRITE_LIFE_NONE -' WRITE_LIFE_NONE
> WRITE_LIFE_MEDIUM -' WRITE_LIFE_MEDIUM
> WRITE_LIFE_LONG -' WRITE_LIFE_LONG
>
>
> Note that, I don't much care about how to manipulate streamid in nvme driver
> in terms of LIFE_NONE or LIFE_NOTSET, since other drivers can handle them
> in different ways. Taking a look at the definition, at least, we don't need
> to assume that those are same at all. For example, if we can expolit this in
> UFS driver, we can pass all the stream ids to the device as context ids.
>
> Thanks,
>
>>
>> Thanks.
>>
>> On 12/12/2017 11:45 AM, Chao Yu wrote:
>>> Hi Hyunchul,
>>>
>>> On 2017/12/12 10:15, Hyunchul Lee wrote:
>>>> Hi Chao,
>>>>
>>>> On 12/11/2017 10:15 PM, Chao Yu wrote:
>>>>> Hi Hyunchul,
>>>>>
>>>>> On 2017/12/1 16:28, Hyunchul Lee wrote:
>>>>>> Hi Chao,
>>>>>>
>>>>>> On 11/30/2017 04:06 PM, Chao Yu wrote:
>>>>>>> Hi Hyunchul,
>>>>>>>
>>>>>>> On 2017/11/28 8:23, Hyunchul Lee wrote:
>>>>>>>> From: Hyunchul Lee <cheol.lee@....com>
>>>>>>>>
>>>>>>>> This implements which hint is passed down to block layer
>>>>>>>> for datas from the specific segment type.
>>>>>>>>
>>>>>>>> segment type hints
>>>>>>>> ------------ -----
>>>>>>>> COLD_NODE & COLD_DATA WRITE_LIFE_EXTREME
>>>>>>>> WARM_DATA WRITE_LIFE_NONE
>>>>>>>> HOT_NODE & WARM_NODE WRITE_LIFE_LONG
>>>>>>>> HOT_DATA WRITE_LIFE_MEDIUM
>>>>>>>> META_DATA WRITE_LIFE_SHORT
>>>>>>>
>>>>>>> Just noticed, if our user do not give the hint via ioctl, f2fs can
>>>>>>> provider hint to lower layer according to hot/cold separation ability,
>>>>>>> it will be okay. But once user give his hint which may be more accurate
>>>>>>> than filesystem, hint converted by f2fs may be wrong.
>>>>>>>
>>>>>>> So what do you think of adding an option to control whether filesystem
>>>>>>> can convert hint user given?
>>>>>>>
>>>>>>
>>>>>> I think it is okay for LIFE_SHORT and LIFE_EXTREME. because they are
>>>>>> converted to different hints.
>>>>>
>>>>> What I mean is introducing a mount option, e.g. fs_iohint,
>>>>> a) w/o fs_iohint, propagate file/inode io_hint to low layer.
>>>>> b) w/ fs_iohint, ignore file/inode io_hint, use io_hint which is generated
>>>>> with filesystem's private rule.
>>>>>
>>>>
>>>> Okay, I will implement this option and send this patch again.
>>>
>>> Let's wait for Jaegeuk's comments first?
>>>
>>>>
>>>> Without fs_iohint, Even if data blocks are moved due to GC,
>>>> we should keep user hints. And if user hints are not given,
>>>> any hints are not passed down to block layer, right?
>>>
>>> Hmm.. that will be a problem, IMO, we can store last user's io_hint into inode
>>> layout, so later when we trigger GC, we can use the last io_hint in inode rather
>>> than giving no hint or fs' hint.
>>>
>>> I think it needs to discuss with original author of IO hint, what is the IO hint
>>> policy when filesystem move block by itself after inode has been released in system.
>>>
>>> Thanks,
>>>
>>>>
>>>> Thank you for comments.
>>>>
>>>>> Thanks,
>>>>>
>>>>>>
>>>>>> file hint segment type io hint
>>>>>> --------- ------------ -------
>>>>>> LIFE_SHORT HOT_DATA LIFE_MEDIUM
>>>>>> LIFE_MEDIUM WARM_DATA LIFE_NONE
>>>>>> LIFE_LONG WARM_DATA LIFE_NONE
>>>>>> LIFE_EXTREME COLD_DATA LIFE_EXTREME
>>>>>>
>>>>>> the problem is that LIFE_MEDIUM and LIFE_LONG are converted to
>>>>>> the same hint, LIFE_NONE. I am not sure that the seperation between
>>>>>> LIFE_MEDIUM and LIFE_LONG is really needed. Because I guess that the
>>>>>> difference between them is a little ambigous for users, and if WARM_DATA
>>>>>> segment has two different hints, it can makes GC non-efficient.
>>>>>>
>>>>>> I wonder your thought about this.
>>>>>>
>>>>>> Thanks.
>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> ------------------------------------------------------------------------------
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>>>>>> _______________________________________________
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>>>>>> Linux-f2fs-devel@...ts.sourceforge.net
>>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>>>
>>>>>
>>>>
>>>> .
>>>>
>>>
>>>
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>
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