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

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Message-id: <001101cee4c8$a51286d0$ef379470$@samsung.com>
Date:	Tue, 19 Nov 2013 09:41:54 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	jaegeuk.kim@...sung.com
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	'谭姝' <shu.tan@...sung.com>
Subject: RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for
 merging contiguous read

Hi

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk.kim@...sung.com]
> Sent: Monday, November 18, 2013 5:11 PM
> To: Chao Yu
> Cc: linux-fsdevel@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-f2fs-devel@...ts.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@...sung.com]
> > > Sent: Monday, November 18, 2013 8:29 AM
> > > To: Chao Yu
> > > Cc: linux-fsdevel@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-f2fs-devel@...ts.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@...sung.com>
> > > > Acked-by: Gu Zheng <guz.fnst@...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

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