RE: [f2fs-dev] [PATCH] f2fs: remove the own bi_private allocation

[Jaegeuk Kim]

2013-12-02 (ì), 14:14 +0800, Chao Yu:
> Hi Kim,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk.kim@xxxxxxxxxxx]
> > Sent: Saturday, November 30, 2013 9:48 AM
> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> > 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@xxxxxxxxxxx>
> > ---
> >  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;
> > +	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.
Thanks,

-- 
Jaegeuk Kim
Samsung

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