[f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Chao Yu]

For better read performance, we add a new function to support for merging contiguous read as the one for write.

v1-->v2:
 o add declarations here as Gu Zheng suggested.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
---
 fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
 fs/f2fs/f2fs.h |    4 ++++
 2 files changed, 49 insertions(+)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index aa3438c..18107cb 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 	return 0;
 }
 
+void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
+{
+	down_read(&sbi->bio_sem);
+	if (sbi->read_bio) {
+		submit_bio(rw, sbi->read_bio);
+		sbi->read_bio = NULL;
+	}
+	up_read(&sbi->bio_sem);
+}
+
+void submit_read_page(struct f2fs_sb_info *sbi, struct page *page,
+					block_t blk_addr, int rw)
+{
+	struct block_device *bdev = sbi->sb->s_bdev;
+	int bio_blocks;
+
+	verify_block_addr(sbi, blk_addr);
+
+	down_read(&sbi->bio_sem);
+
+	if (sbi->read_bio && sbi->last_read_block != blk_addr - 1) {
+		submit_bio(rw, sbi->read_bio);
+		sbi->read_bio = NULL;
+	}
+
+alloc_new:
+	if (sbi->read_bio == NULL) {
+		bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
+		sbi->read_bio = f2fs_bio_alloc(bdev, bio_blocks);
+		sbi->read_bio->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
+		sbi->read_bio->bi_end_io = read_end_io;
+	}
+
+	if (bio_add_page(sbi->read_bio, page, PAGE_CACHE_SIZE, 0) <
+							PAGE_CACHE_SIZE) {
+		submit_bio(rw, sbi->read_bio);
+		sbi->read_bio = NULL;
+		goto alloc_new;
+	}
+
+	sbi->last_read_block = blk_addr;
+
+	up_read(&sbi->bio_sem);
+}
+
 /*
  * This function should be used by the data read flow only where it
  * does not check the "create" flag that indicates block allocation.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 89dc750..bfe9d87 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -359,6 +359,8 @@ struct f2fs_sb_info {
 
 	/* for segment-related operations */
 	struct f2fs_sm_info *sm_info;		/* segment manager */
+	struct bio *read_bio;			/* read bios to merge */
+	sector_t last_read_block;		/* last read block number */
 	struct bio *bio[NR_PAGE_TYPE];		/* bios to merge */
 	sector_t last_block_in_bio[NR_PAGE_TYPE];	/* last block number */
 	struct rw_semaphore bio_sem;		/* IO semaphore */
@@ -1111,6 +1113,8 @@ struct page *find_data_page(struct inode *, pgoff_t, bool);
 struct page *get_lock_data_page(struct inode *, pgoff_t);
 struct page *get_new_data_page(struct inode *, struct page *, pgoff_t, bool);
 int f2fs_readpage(struct f2fs_sb_info *, struct page *, block_t, int);
+void f2fs_submit_read_bio(struct f2fs_sb_info *, int);
+void submit_read_page(struct f2fs_sb_info *, struct page *, block_t, int);
 int do_write_data_page(struct page *);
 
 /*
-- 
1.7.9.5

Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Jaegeuk Kim]

Hi Chao,

2013-11-16 (토), 14:14 +0800, Chao Yu:
> For better read performance, we add a new function to support for merging contiguous read as the one for write.

Please consider 80 columns for the description.
I cannot fix this at every time though. :(

> 
> v1-->v2:
>  o add declarations here as Gu Zheng suggested.
> 
> Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> ---
>  fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
>  fs/f2fs/f2fs.h |    4 ++++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index aa3438c..18107cb 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
>  	return 0;
>  }
>  
> +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
> +{
> +	down_read(&sbi->bio_sem);

Is there any reason to use down_read()?
It seems that we need to declare sbi->bio_read and sbi->bio_write
instead of sbi->bio_sem.
In addition to that, we need to use down_write(&sbi->bio_read) here.

> +	if (sbi->read_bio) {
> +		submit_bio(rw, sbi->read_bio);
> +		sbi->read_bio = NULL;
> +	}
> +	up_read(&sbi->bio_sem);

up_write(&sbi->bio_read);

> +}
> +
> +void submit_read_page(struct f2fs_sb_info *sbi, struct page *page,
> +					block_t blk_addr, int rw)
> +{
> +	struct block_device *bdev = sbi->sb->s_bdev;
> +	int bio_blocks;
> +
> +	verify_block_addr(sbi, blk_addr);
> +
> +	down_read(&sbi->bio_sem);

down_write(&sbi->bio_read);

> +
> +	if (sbi->read_bio && sbi->last_read_block != blk_addr - 1) {
> +		submit_bio(rw, sbi->read_bio);
> +		sbi->read_bio = NULL;
> +	}
> +
> +alloc_new:
> +	if (sbi->read_bio == NULL) {
> +		bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
> +		sbi->read_bio = f2fs_bio_alloc(bdev, bio_blocks);
> +		sbi->read_bio->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
> +		sbi->read_bio->bi_end_io = read_end_io;
> +	}
> +
> +	if (bio_add_page(sbi->read_bio, page, PAGE_CACHE_SIZE, 0) <
> +							PAGE_CACHE_SIZE) {
> +		submit_bio(rw, sbi->read_bio);
> +		sbi->read_bio = NULL;
> +		goto alloc_new;
> +	}
> +
> +	sbi->last_read_block = blk_addr;
> +
> +	up_read(&sbi->bio_sem);

up_write(&sbi->bio_read);

> +}
> +
>  /*
>   * This function should be used by the data read flow only where it
>   * does not check the "create" flag that indicates block allocation.
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 89dc750..bfe9d87 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -359,6 +359,8 @@ struct f2fs_sb_info {
>  
>  	/* for segment-related operations */
>  	struct f2fs_sm_info *sm_info;		/* segment manager */
> +	struct bio *read_bio;			/* read bios to merge */
> +	sector_t last_read_block;		/* last read block number */
>  	struct bio *bio[NR_PAGE_TYPE];		/* bios to merge */
>  	sector_t last_block_in_bio[NR_PAGE_TYPE];	/* last block number */
>  	struct rw_semaphore bio_sem;		/* IO semaphore */
> @@ -1111,6 +1113,8 @@ struct page *find_data_page(struct inode *, pgoff_t, bool);
>  struct page *get_lock_data_page(struct inode *, pgoff_t);
>  struct page *get_new_data_page(struct inode *, struct page *, pgoff_t, bool);
>  int f2fs_readpage(struct f2fs_sb_info *, struct page *, block_t, int);
> +void f2fs_submit_read_bio(struct f2fs_sb_info *, int);
> +void submit_read_page(struct f2fs_sb_info *, struct page *, block_t, int);
>  int do_write_data_page(struct page *);
>  
>  /*

-- 
Jaegeuk Kim
Samsung

RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Chao Yu]

Hi Kim,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> Sent: Monday, November 18, 2013 8:29 AM
> To: Chao Yu
> Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net; 谭姝
> Subject: Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read
> 
> Hi Chao,
> 
> 2013-11-16 (토), 14:14 +0800, Chao Yu:
> > For better read performance, we add a new function to support for merging contiguous read as the one for write.
> 
> Please consider 80 columns for the description.
> I cannot fix this at every time though. :(

Got it, sorry about my carelessness in previous patch.

> 
> >
> > v1-->v2:
> >  o add declarations here as Gu Zheng suggested.
> >
> > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> > ---
> >  fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
> >  fs/f2fs/f2fs.h |    4 ++++
> >  2 files changed, 49 insertions(+)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index aa3438c..18107cb 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
> >  	return 0;
> >  }
> >
> > +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
> > +{
> > +	down_read(&sbi->bio_sem);
> 
> Is there any reason to use down_read()?

Isn't that we use bio_sem to let w/r or w/w submitting be mutex?

> It seems that we need to declare sbi->bio_read and sbi->bio_write
> instead of sbi->bio_sem.
> In addition to that, we need to use down_write(&sbi->bio_read) here.

If so, it looks similar between (struct rw_semaphore) sbi->bio_read 
and (struct bio *) sbi->read_bio.
How about using read_bio_sem/rbio_sem to differentiate 
from sbi->read_bio?

> 
> > +	if (sbi->read_bio) {
> > +		submit_bio(rw, sbi->read_bio);
> > +		sbi->read_bio = NULL;
> > +	}
> > +	up_read(&sbi->bio_sem);
> 
> up_write(&sbi->bio_read);
> 
> > +}
> > +
> > +void submit_read_page(struct f2fs_sb_info *sbi, struct page *page,
> > +					block_t blk_addr, int rw)
> > +{
> > +	struct block_device *bdev = sbi->sb->s_bdev;
> > +	int bio_blocks;
> > +
> > +	verify_block_addr(sbi, blk_addr);
> > +
> > +	down_read(&sbi->bio_sem);
> 
> down_write(&sbi->bio_read);
> 
> > +
> > +	if (sbi->read_bio && sbi->last_read_block != blk_addr - 1) {
> > +		submit_bio(rw, sbi->read_bio);
> > +		sbi->read_bio = NULL;
> > +	}
> > +
> > +alloc_new:
> > +	if (sbi->read_bio == NULL) {
> > +		bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
> > +		sbi->read_bio = f2fs_bio_alloc(bdev, bio_blocks);
> > +		sbi->read_bio->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
> > +		sbi->read_bio->bi_end_io = read_end_io;
> > +	}
> > +
> > +	if (bio_add_page(sbi->read_bio, page, PAGE_CACHE_SIZE, 0) <
> > +							PAGE_CACHE_SIZE) {
> > +		submit_bio(rw, sbi->read_bio);
> > +		sbi->read_bio = NULL;
> > +		goto alloc_new;
> > +	}
> > +
> > +	sbi->last_read_block = blk_addr;
> > +
> > +	up_read(&sbi->bio_sem);
> 
> up_write(&sbi->bio_read);
> 
> > +}
> > +
> >  /*
> >   * This function should be used by the data read flow only where it
> >   * does not check the "create" flag that indicates block allocation.
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 89dc750..bfe9d87 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -359,6 +359,8 @@ struct f2fs_sb_info {
> >
> >  	/* for segment-related operations */
> >  	struct f2fs_sm_info *sm_info;		/* segment manager */
> > +	struct bio *read_bio;			/* read bios to merge */
> > +	sector_t last_read_block;		/* last read block number */
> >  	struct bio *bio[NR_PAGE_TYPE];		/* bios to merge */
> >  	sector_t last_block_in_bio[NR_PAGE_TYPE];	/* last block number */
> >  	struct rw_semaphore bio_sem;		/* IO semaphore */
> > @@ -1111,6 +1113,8 @@ struct page *find_data_page(struct inode *, pgoff_t, bool);
> >  struct page *get_lock_data_page(struct inode *, pgoff_t);
> >  struct page *get_new_data_page(struct inode *, struct page *, pgoff_t, bool);
> >  int f2fs_readpage(struct f2fs_sb_info *, struct page *, block_t, int);
> > +void f2fs_submit_read_bio(struct f2fs_sb_info *, int);
> > +void submit_read_page(struct f2fs_sb_info *, struct page *, block_t, int);
> >  int do_write_data_page(struct page *);
> >
> >  /*
> 
> --
> Jaegeuk Kim
> Samsung

RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Jaegeuk Kim]

Hi,

2013-11-18 (월), 09:37 +0800, Chao Yu:
> Hi Kim,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> > Sent: Monday, November 18, 2013 8:29 AM
> > To: Chao Yu
> > Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net; 谭姝
> > Subject: Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read
> > 
> > Hi Chao,
> > 
> > 2013-11-16 (토), 14:14 +0800, Chao Yu:
> > > For better read performance, we add a new function to support for merging contiguous read as the one for write.
> > 
> > Please consider 80 columns for the description.
> > I cannot fix this at every time though. :(
> 
> Got it, sorry about my carelessness in previous patch.
> 
> > 
> > >
> > > v1-->v2:
> > >  o add declarations here as Gu Zheng suggested.
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > > Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> > > ---
> > >  fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
> > >  fs/f2fs/f2fs.h |    4 ++++
> > >  2 files changed, 49 insertions(+)
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index aa3438c..18107cb 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
> > >  	return 0;
> > >  }
> > >
> > > +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
> > > +{
> > > +	down_read(&sbi->bio_sem);
> > 
> > Is there any reason to use down_read()?
> 
> Isn't that we use bio_sem to let w/r or w/w submitting be mutex?

As I examined the bio_sem, I think we don't need to use a semaphore for
read and write IOs.
Just it is enough to use a mutex for writes only.

> 
> > It seems that we need to declare sbi->bio_read and sbi->bio_write
> > instead of sbi->bio_sem.
> > In addition to that, we need to use down_write(&sbi->bio_read) here.
> 
> If so, it looks similar between (struct rw_semaphore) sbi->bio_read 
> and (struct bio *) sbi->read_bio.
> How about using read_bio_sem/rbio_sem to differentiate 
> from sbi->read_bio?

I think sbi->write_mutex and sbi->read_mutex are much better.

Could you refer the following patches?
Thanks,

-- 
Jaegeuk Kim
Samsung

Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Gu Zheng]

On 11/18/2013 05:11 PM, Jaegeuk Kim wrote:

> Hi,
> 
> 2013-11-18 (월), 09:37 +0800, Chao Yu:
>> Hi Kim,
>>
>>> -----Original Message-----
>>> From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
>>> Sent: Monday, November 18, 2013 8:29 AM
>>> To: Chao Yu
>>> Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net; 谭姝
>>> Subject: Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read
>>>
>>> Hi Chao,
>>>
>>> 2013-11-16 (토), 14:14 +0800, Chao Yu:
>>>> For better read performance, we add a new function to support for merging contiguous read as the one for write.
>>>
>>> Please consider 80 columns for the description.
>>> I cannot fix this at every time though. :(
>>
>> Got it, sorry about my carelessness in previous patch.
>>
>>>
>>>>
>>>> v1-->v2:
>>>>  o add declarations here as Gu Zheng suggested.
>>>>
>>>> Signed-off-by: Chao Yu <chao2.yu@samsung.com>
>>>> Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
>>>> ---
>>>>  fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
>>>>  fs/f2fs/f2fs.h |    4 ++++
>>>>  2 files changed, 49 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index aa3438c..18107cb 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
>>>>  	return 0;
>>>>  }
>>>>
>>>> +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
>>>> +{
>>>> +	down_read(&sbi->bio_sem);
>>>
>>> Is there any reason to use down_read()?
>>
>> Isn't that we use bio_sem to let w/r or w/w submitting be mutex?
> 
> As I examined the bio_sem, I think we don't need to use a semaphore for
> read and write IOs.
> Just it is enough to use a mutex for writes only.

Agree. Mutex is more suitable here, we just want to protect the write bio
related fields in the write patch, no relations to read.

> 
>>
>>> It seems that we need to declare sbi->bio_read and sbi->bio_write
>>> instead of sbi->bio_sem.
>>> In addition to that, we need to use down_write(&sbi->bio_read) here.
>>
>> If so, it looks similar between (struct rw_semaphore) sbi->bio_read 
>> and (struct bio *) sbi->read_bio.
>> How about using read_bio_sem/rbio_sem to differentiate 
>> from sbi->read_bio?
> 
> I think sbi->write_mutex and sbi->read_mutex are much better.

It's more reasonable and readable.

Thanks,
Gu

> 
> Could you refer the following patches?
> Thanks,
> 

RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Chao Yu]

Hi

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> Sent: Monday, November 18, 2013 5:11 PM
> To: Chao Yu
> Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net; '谭姝'
> Subject: RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for
> merging contiguous read
> 
> Hi,
> 
> 2013-11-18 (월), 09:37 +0800, Chao Yu:
> > Hi Kim,
> >
> > > -----Original Message-----
> > > From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> > > Sent: Monday, November 18, 2013 8:29 AM
> > > To: Chao Yu
> > > Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net; 谭姝
> > > Subject: Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for
> merging contiguous read
> > >
> > > Hi Chao,
> > >
> > > 2013-11-16 (토), 14:14 +0800, Chao Yu:
> > > > For better read performance, we add a new function to support for merging
> contiguous read as the one for write.
> > >
> > > Please consider 80 columns for the description.
> > > I cannot fix this at every time though. :(
> >
> > Got it, sorry about my carelessness in previous patch.
> >
> > >
> > > >
> > > > v1-->v2:
> > > >  o add declarations here as Gu Zheng suggested.
> > > >
> > > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > > > Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> > > > ---
> > > >  fs/f2fs/data.c |   45
> +++++++++++++++++++++++++++++++++++++++++++++
> > > >  fs/f2fs/f2fs.h |    4 ++++
> > > >  2 files changed, 49 insertions(+)
> > > >
> > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > > index aa3438c..18107cb 100644
> > > > --- a/fs/f2fs/data.c
> > > > +++ b/fs/f2fs/data.c
> > > > @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct
> page *page,
> > > >  	return 0;
> > > >  }
> > > >
> > > > +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
> > > > +{
> > > > +	down_read(&sbi->bio_sem);
> > >
> > > Is there any reason to use down_read()?
> >
> > Isn't that we use bio_sem to let w/r or w/w submitting be mutex?
> 
> As I examined the bio_sem, I think we don't need to use a semaphore for
> read and write IOs.
> Just it is enough to use a mutex for writes only.

Agreed, it could also improve efficiency of read/write request concurrent.

> 
> >
> > > It seems that we need to declare sbi->bio_read and sbi->bio_write
> > > instead of sbi->bio_sem.
> > > In addition to that, we need to use down_write(&sbi->bio_read) here.
> >
> > If so, it looks similar between (struct rw_semaphore) sbi->bio_read
> > and (struct bio *) sbi->read_bio.
> > How about using read_bio_sem/rbio_sem to differentiate
> > from sbi->read_bio?
> 
> I think sbi->write_mutex and sbi->read_mutex are much better.
> 
> Could you refer the following patches?

It's better, I will refer your patch.
And how about this following patch to reduce race of write_mutex 
between DATA/NODE/META writer?

> Thanks,
> 
> --
> Jaegeuk Kim
> Samsung