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Subject: Re: [PATCH v2] f2fs: separate NOCoW and pinfile semantics
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20190719073903.9138-1-yuchao0@huawei.com>
 <20190723023640.GC60778@jaegeuk-macbookpro.roam.corp.google.com>
 <d4d064a2-2b3c-3536-6488-39e7cfdb1ea4@huawei.com>
 <20190729055738.GA95664@jaegeuk-macbookpro.roam.corp.google.com>
 <07cd3aba-3516-9ba5-286e-277abb98e244@huawei.com>
 <20190730180231.GB76478@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <00e70eb1-c4fa-a6c9-69d7-71ff995c7d6c@huawei.com>
Date:   Wed, 31 Jul 2019 17:55:18 +0800
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On 2019/7/31 2:02, Jaegeuk Kim wrote:
> On 07/29, Chao Yu wrote:
>> On 2019/7/29 13:57, Jaegeuk Kim wrote:
>>> On 07/23, Chao Yu wrote:
>>>> On 2019/7/23 10:36, Jaegeuk Kim wrote:
>>>>> On 07/19, Chao Yu wrote:
>>>>>> Pinning a file is heavy, because skipping pinned files make GC
>>>>>> running with heavy load or no effect.
>>>>>
>>>>> Pinned file is a part of NOCOW files, so I don't think we can simply drop it
>>>>> for backward compatibility.
>>>>
>>>> Yes,
>>>>
>>>> But what I concerned is that pin file is too heavy, so in order to satisfy below
>>>> demand, how about introducing pin_file_2 flag to triggering IPU only during
>>>> flush/writeback.
>>>
>>> That can be done by cold files?
>>
>> Then it may inherit property of cold type file, e.g. a) goes into cold area; b)
>> update with very low frequency.
>>
>> Actually pin_file_2 could be used by db-wal/log file, which are updated
>> frequently, and should go to hot/warm area, it does not match above two property.
> 
> How about considering another name like "IPU-only mode"?
> 
>               fallocate         write    Flag         GC
> Pin_file:     preallocate       IPU      FS_NOCOW_FL  Not allowed
> IPU_file:     Not preallocate   IPU      N/A          Default by temperature

One question, do we need preallocate physical block address for IPU_file as
Pin_file? since it can enhance db file's sequential read performance, not sure,
db can handle random data in preallocated blocks.

Other behaviors looks good to me. :)

I plan to use last bit in inode.i_inline to store this flag.

> Cold_file:    Not preallocate   IPU      N/A          Move in cold area
> Hot_file:     Not preallocate   IPU/OPU  N/A          Move in hot area

Should hot file be gced to hot area? That would mix new hot data with old 'hot'
data which actually become cold.

Thanks,

> 
>>
>> Thank,
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>> So that this patch propose to separate nocow and pinfile semantics:
>>>>>> - NOCoW flag can only be set on regular file.
>>>>>> - NOCoW file will only trigger IPU at common writeback/flush.
>>>>>> - NOCow file will do OPU during GC.
>>>>>>
>>>>>> For the demand of 1) avoid fragment of file's physical block and
>>>>>> 2) userspace don't care about file's specific physical address,
>>>>>> tagging file as NOCoW will be cheaper than pinned one.
>>>>
>>>> ^^^
>>>>
>>>> Thanks,
>>>>
>>>>>>
>>>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>>>> ---
>>>>>> v2:
>>>>>> - rebase code to fix compile error.
>>>>>>  fs/f2fs/data.c |  3 ++-
>>>>>>  fs/f2fs/f2fs.h |  1 +
>>>>>>  fs/f2fs/file.c | 22 +++++++++++++++++++---
>>>>>>  3 files changed, 22 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>> index a2a28bb269bf..15fb8954c363 100644
>>>>>> --- a/fs/f2fs/data.c
>>>>>> +++ b/fs/f2fs/data.c
>>>>>> @@ -1884,7 +1884,8 @@ static inline bool check_inplace_update_policy(struct inode *inode,
>>>>>>  
>>>>>>  bool f2fs_should_update_inplace(struct inode *inode, struct f2fs_io_info *fio)
>>>>>>  {
>>>>>> -	if (f2fs_is_pinned_file(inode))
>>>>>> +	if (f2fs_is_pinned_file(inode) ||
>>>>>> +			F2FS_I(inode)->i_flags & F2FS_NOCOW_FL)
>>>>>>  		return true;
>>>>>>  
>>>>>>  	/* if this is cold file, we should overwrite to avoid fragmentation */
>>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>>> index 596ab3e1dd7b..f6c5a3d2e659 100644
>>>>>> --- a/fs/f2fs/f2fs.h
>>>>>> +++ b/fs/f2fs/f2fs.h
>>>>>> @@ -2374,6 +2374,7 @@ static inline void f2fs_change_bit(unsigned int nr, char *addr)
>>>>>>  #define F2FS_NOATIME_FL			0x00000080 /* do not update atime */
>>>>>>  #define F2FS_INDEX_FL			0x00001000 /* hash-indexed directory */
>>>>>>  #define F2FS_DIRSYNC_FL			0x00010000 /* dirsync behaviour (directories only) */
>>>>>> +#define F2FS_NOCOW_FL			0x00800000 /* Do not cow file */
>>>>>>  #define F2FS_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
>>>>>>  
>>>>>>  /* Flags that should be inherited by new inodes from their parent. */
>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>>> index 7ca545874060..ae0fec54cac6 100644
>>>>>> --- a/fs/f2fs/file.c
>>>>>> +++ b/fs/f2fs/file.c
>>>>>> @@ -1692,6 +1692,7 @@ static const struct {
>>>>>>  	{ F2FS_NOATIME_FL,	FS_NOATIME_FL },
>>>>>>  	{ F2FS_INDEX_FL,	FS_INDEX_FL },
>>>>>>  	{ F2FS_DIRSYNC_FL,	FS_DIRSYNC_FL },
>>>>>> +	{ F2FS_NOCOW_FL,	FS_NOCOW_FL },
>>>>>>  	{ F2FS_PROJINHERIT_FL,	FS_PROJINHERIT_FL },
>>>>>>  };
>>>>>>  
>>>>>> @@ -1715,7 +1716,8 @@ static const struct {
>>>>>>  		FS_NODUMP_FL |		\
>>>>>>  		FS_NOATIME_FL |		\
>>>>>>  		FS_DIRSYNC_FL |		\
>>>>>> -		FS_PROJINHERIT_FL)
>>>>>> +		FS_PROJINHERIT_FL |	\
>>>>>> +		FS_NOCOW_FL)
>>>>>>  
>>>>>>  /* Convert f2fs on-disk i_flags to FS_IOC_{GET,SET}FLAGS flags */
>>>>>>  static inline u32 f2fs_iflags_to_fsflags(u32 iflags)
>>>>>> @@ -1753,8 +1755,6 @@ static int f2fs_ioc_getflags(struct file *filp, unsigned long arg)
>>>>>>  		fsflags |= FS_ENCRYPT_FL;
>>>>>>  	if (f2fs_has_inline_data(inode) || f2fs_has_inline_dentry(inode))
>>>>>>  		fsflags |= FS_INLINE_DATA_FL;
>>>>>> -	if (is_inode_flag_set(inode, FI_PIN_FILE))
>>>>>> -		fsflags |= FS_NOCOW_FL;
>>>>>>  
>>>>>>  	fsflags &= F2FS_GETTABLE_FS_FL;
>>>>>>  
>>>>>> @@ -1794,6 +1794,22 @@ static int f2fs_ioc_setflags(struct file *filp, unsigned long arg)
>>>>>>  	if (ret)
>>>>>>  		goto out;
>>>>>>  
>>>>>> +	if ((fsflags ^ old_fsflags) & FS_NOCOW_FL) {
>>>>>> +		if (!S_ISREG(inode->i_mode)) {
>>>>>> +			ret = -EINVAL;
>>>>>> +			goto out;
>>>>>> +		}
>>>>>> +
>>>>>> +		if (f2fs_should_update_outplace(inode, NULL)) {
>>>>>> +			ret = -EINVAL;
>>>>>> +			goto out;
>>>>>> +		}
>>>>>> +
>>>>>> +		ret = f2fs_convert_inline_inode(inode);
>>>>>> +		if (ret)
>>>>>> +			goto out;
>>>>>> +	}
>>>>>> +
>>>>>>  	ret = f2fs_setflags_common(inode, iflags,
>>>>>>  			f2fs_fsflags_to_iflags(F2FS_SETTABLE_FS_FL));
>>>>>>  out:
>>>>>> -- 
>>>>>> 2.18.0.rc1
>>>>> .
>>>>>
>>> .
>>>
> .
>