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Date:   Mon, 19 Nov 2018 16:35:20 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Omar Sandoval <osandov@...ndov.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
        linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>,
        linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 13/19] iomap & xfs: only account for new added page

On Thu, Nov 15, 2018 at 05:46:58PM -0800, Omar Sandoval wrote:
> On Thu, Nov 15, 2018 at 04:53:00PM +0800, Ming Lei wrote:
> > After multi-page is enabled, one new page may be merged to a segment
> > even though it is a new added page.
> > 
> > This patch deals with this issue by post-check in case of merge, and
> > only a freshly new added page need to be dealt with for iomap & xfs.
> > 
> > Cc: Dave Chinner <dchinner@...hat.com>
> > Cc: Kent Overstreet <kent.overstreet@...il.com>
> > Cc: Mike Snitzer <snitzer@...hat.com>
> > Cc: dm-devel@...hat.com
> > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > Cc: linux-fsdevel@...r.kernel.org
> > Cc: Shaohua Li <shli@...nel.org>
> > Cc: linux-raid@...r.kernel.org
> > Cc: linux-erofs@...ts.ozlabs.org
> > Cc: David Sterba <dsterba@...e.com>
> > Cc: linux-btrfs@...r.kernel.org
> > Cc: Darrick J. Wong <darrick.wong@...cle.com>
> > Cc: linux-xfs@...r.kernel.org
> > Cc: Gao Xiang <gaoxiang25@...wei.com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Theodore Ts'o <tytso@....edu>
> > Cc: linux-ext4@...r.kernel.org
> > Cc: Coly Li <colyli@...e.de>
> > Cc: linux-bcache@...r.kernel.org
> > Cc: Boaz Harrosh <ooo@...ctrozaur.com>
> > Cc: Bob Peterson <rpeterso@...hat.com>
> > Cc: cluster-devel@...hat.com
> > Signed-off-by: Ming Lei <ming.lei@...hat.com>
> > ---
> >  fs/iomap.c          | 22 ++++++++++++++--------
> >  fs/xfs/xfs_aops.c   | 10 ++++++++--
> >  include/linux/bio.h | 11 +++++++++++
> >  3 files changed, 33 insertions(+), 10 deletions(-)
> > 
> > diff --git a/fs/iomap.c b/fs/iomap.c
> > index df0212560b36..a1b97a5c726a 100644
> > --- a/fs/iomap.c
> > +++ b/fs/iomap.c
> > @@ -288,6 +288,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> >  	loff_t orig_pos = pos;
> >  	unsigned poff, plen;
> >  	sector_t sector;
> > +	bool need_account = false;
> >  
> >  	if (iomap->type == IOMAP_INLINE) {
> >  		WARN_ON_ONCE(pos);
> > @@ -313,18 +314,15 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> >  	 */
> >  	sector = iomap_sector(iomap, pos);
> >  	if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
> > -		if (__bio_try_merge_page(ctx->bio, page, plen, poff))
> > +		if (__bio_try_merge_page(ctx->bio, page, plen, poff)) {
> > +			need_account = iop && bio_is_last_segment(ctx->bio,
> > +					page, plen, poff);
> 
> It's redundant to make this iop && ... since you already check
> iop && need_account below. Maybe rename it to added_page? Also, this
> indentation is wack.

We may avoid to call bio_is_last_segment() in case of !iop, and will
fix the indentation.

Looks added_page is one better name.

> 
> >  			goto done;
> > +		}
> >  		is_contig = true;
> >  	}
> >  
> > -	/*
> > -	 * If we start a new segment we need to increase the read count, and we
> > -	 * need to do so before submitting any previous full bio to make sure
> > -	 * that we don't prematurely unlock the page.
> > -	 */
> > -	if (iop)
> > -		atomic_inc(&iop->read_count);
> > +	need_account = true;
> >  
> >  	if (!ctx->bio || !is_contig || bio_full(ctx->bio)) {
> >  		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
> > @@ -347,6 +345,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> >  	__bio_add_page(ctx->bio, page, plen, poff);
> >  done:
> >  	/*
> > +	 * If we add a new page we need to increase the read count, and we
> > +	 * need to do so before submitting any previous full bio to make sure
> > +	 * that we don't prematurely unlock the page.
> > +	 */
> > +	if (iop && need_account)
> > +		atomic_inc(&iop->read_count);
> > +
> > +	/*
> >  	 * Move the caller beyond our range so that it keeps making progress.
> >  	 * For that we have to include any leading non-uptodate ranges, but
> >  	 * we can skip trailing ones as they will be handled in the next
> > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> > index 1f1829e506e8..d8e9cc9f751a 100644
> > --- a/fs/xfs/xfs_aops.c
> > +++ b/fs/xfs/xfs_aops.c
> > @@ -603,6 +603,7 @@ xfs_add_to_ioend(
> >  	unsigned		len = i_blocksize(inode);
> >  	unsigned		poff = offset & (PAGE_SIZE - 1);
> >  	sector_t		sector;
> > +	bool			need_account;
> >  
> >  	sector = xfs_fsb_to_db(ip, wpc->imap.br_startblock) +
> >  		((offset - XFS_FSB_TO_B(mp, wpc->imap.br_startoff)) >> 9);
> > @@ -617,13 +618,18 @@ xfs_add_to_ioend(
> >  	}
> >  
> >  	if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff)) {
> > -		if (iop)
> > -			atomic_inc(&iop->write_count);
> > +		need_account = true;
> >  		if (bio_full(wpc->ioend->io_bio))
> >  			xfs_chain_bio(wpc->ioend, wbc, bdev, sector);
> >  		__bio_add_page(wpc->ioend->io_bio, page, len, poff);
> > +	} else {
> > +		need_account = iop && bio_is_last_segment(wpc->ioend->io_bio,
> > +				page, len, poff);
> 
> Same here, no need for iop &&, rename it added_page, indentation is off.
> 
> >  	}
> >  
> > +	if (iop && need_account)
> > +		atomic_inc(&iop->write_count);
> > +
> >  	wpc->ioend->io_size += len;
> >  }
> >  
> > diff --git a/include/linux/bio.h b/include/linux/bio.h
> > index 1a2430a8b89d..5040e9a2eb09 100644
> > --- a/include/linux/bio.h
> > +++ b/include/linux/bio.h
> > @@ -341,6 +341,17 @@ static inline struct bio_vec *bio_last_bvec_all(struct bio *bio)
> >  	return &bio->bi_io_vec[bio->bi_vcnt - 1];
> >  }
> >  
> > +/* iomap needs this helper to deal with sub-pagesize bvec */
> > +static inline bool bio_is_last_segment(struct bio *bio, struct page *page,
> > +		unsigned int len, unsigned int off)
> 
> Indentation.

OK.

Thanks,
Ming

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