Re: [PATCH] f2fs: remove the own bi_private allocation

[Chao Yu <chao2.yu@samsung.com>]

Hi Kim,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> Sent: Monday, December 02, 2013 4:15 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] f2fs: remove the own bi_private allocation
> 
> 2013-12-02 (월), 14:14 +0800, Chao Yu:
> > Hi Kim,
> >
> > > -----Original Message-----
> > > From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> > > Sent: Saturday, November 30, 2013 9:48 AM
> > > Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net
> > > Subject: [f2fs-dev] [PATCH] f2fs: remove the own bi_private allocation
> > >
> > > Previously f2fs allocates its own bi_private data structure all the time even
> > > though we don't use it. But, can we remove this bi_private allocation?
> > >
> > > This patch removes such the additional bi_private allocation.
> > >
> > > 1. Retrieve f2fs_sb_info from its page->mapping->host->i_sb.
> > >  - This removes the usecases of bi_private in end_io.
> > >
> > > 2. Use bi_private only when we really need it.
> > >  - The bi_private is used only when the checkpoint procedure is conducted.
> > >  - When conducting the checkpoint, f2fs submits a META_FLUSH bio to wait its bio
> > > completion.
> > >  - Since we have no dependancies to remove bi_private now, let's just use
> > >  bi_private pointer as the completion pointer.
> > >
> > > Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
> > > ---
> > >  fs/f2fs/segment.c | 43 ++++++++++++++++---------------------------
> > >  fs/f2fs/segment.h |  7 -------
> > >  2 files changed, 16 insertions(+), 34 deletions(-)
> > >
> > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > index 0387863..0db4027 100644
> > > --- a/fs/f2fs/segment.c
> > > +++ b/fs/f2fs/segment.c
> > > @@ -791,7 +791,7 @@ static void f2fs_end_io_write(struct bio *bio, int err)
> > >  {
> > >  	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
> > >  	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
> > > -	struct bio_private *p = bio->bi_private;

		f2fs_bug_on(unlikely(!bvec->bv_page->mapping));

> > > +	struct f2fs_sb_info *sbi = F2FS_SB(bvec->bv_page->mapping->host->i_sb);
> >
> > I'm not sure whether bvec->bv_page->mapping will be set to NULL in the flow
> > where may not check WRITEBACK flag of page. Is it possible?
> 
> The mapping should be not NULL cause it is a writebacking page.
> Otherwise, it's a bug.

If so, should we add additional code as above?

Regards,
Yu

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


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