Re: [PATCH] f2fs: use BIO_MAX_PAGES for bio allocation

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Thu, Oct 27, 2016 at 06:28:04PM +0800, Chao Yu wrote:
> On 2016/10/19 2:48, Jaegeuk Kim wrote:
> > We don't need to allocate bio partially in order to maximize sequential writes.
> 
> We are going to allocate bio with max size supposing that there will be more
> opportunity to merge small IOs into one bio. Otherwise, if MAX_BIO_BLOCKS is
> smaller than BIO_MAX_PAGES, less IOs can be merged. Is my understanding correct?

Yes. When I test /dev/md0 with ramdisks, this happens and results in lower
performance than other filesystems.

Thanks,

> 
> Thanks,
> 
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >  fs/f2fs/checkpoint.c |  2 +-
> >  fs/f2fs/data.c       |  4 +---
> >  fs/f2fs/node.c       |  3 +--
> >  fs/f2fs/segment.c    |  4 ++--
> >  fs/f2fs/segment.h    | 17 +++--------------
> >  5 files changed, 8 insertions(+), 22 deletions(-)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 654f5d7..157b7fd 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -228,7 +228,7 @@ void ra_meta_pages_cond(struct f2fs_sb_info *sbi, pgoff_t index)
> >  	f2fs_put_page(page, 0);
> >  
> >  	if (readahead)
> > -		ra_meta_pages(sbi, index, MAX_BIO_BLOCKS(sbi), META_POR, true);
> > +		ra_meta_pages(sbi, index, BIO_MAX_PAGES, META_POR, true);
> >  }
> >  
> >  static int f2fs_write_meta_page(struct page *page,
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 77cd9ac..fe8ce5a 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -307,10 +307,8 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
> >  		__submit_merged_bio(io);
> >  alloc_new:
> >  	if (io->bio == NULL) {
> > -		int bio_blocks = MAX_BIO_BLOCKS(sbi);
> > -
> >  		io->bio = __bio_alloc(sbi, fio->new_blkaddr,
> > -						bio_blocks, is_read);
> > +						BIO_MAX_PAGES, is_read);
> >  		io->fio = *fio;
> >  	}
> >  
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > index 69c42e2..285e2a5 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -2101,7 +2101,6 @@ int restore_node_summary(struct f2fs_sb_info *sbi,
> >  	struct f2fs_node *rn;
> >  	struct f2fs_summary *sum_entry;
> >  	block_t addr;
> > -	int bio_blocks = MAX_BIO_BLOCKS(sbi);
> >  	int i, idx, last_offset, nrpages;
> >  
> >  	/* scan the node segment */
> > @@ -2110,7 +2109,7 @@ int restore_node_summary(struct f2fs_sb_info *sbi,
> >  	sum_entry = &sum->entries[0];
> >  
> >  	for (i = 0; i < last_offset; i += nrpages, addr += nrpages) {
> > -		nrpages = min(last_offset - i, bio_blocks);
> > +		nrpages = min(last_offset - i, BIO_MAX_PAGES);
> >  
> >  		/* readahead node pages */
> >  		ra_meta_pages(sbi, addr, nrpages, META_POR, true);
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 7a7e3f1..a21a1a3 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -2355,10 +2355,10 @@ static void build_sit_entries(struct f2fs_sb_info *sbi)
> >  	int sit_blk_cnt = SIT_BLK_CNT(sbi);
> >  	unsigned int i, start, end;
> >  	unsigned int readed, start_blk = 0;
> > -	int nrpages = MAX_BIO_BLOCKS(sbi) * 8;
> >  
> >  	do {
> > -		readed = ra_meta_pages(sbi, start_blk, nrpages, META_SIT, true);
> > +		readed = ra_meta_pages(sbi, start_blk, BIO_MAX_PAGES,
> > +							META_SIT, true);
> >  
> >  		start = start_blk * sit_i->sents_per_block;
> >  		end = (start_blk + readed) * sit_i->sents_per_block;
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index a6efb5c..d8ff069 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -102,8 +102,6 @@
> >  	(((sector_t)blk_addr) << F2FS_LOG_SECTORS_PER_BLOCK)
> >  #define SECTOR_TO_BLOCK(sectors)					\
> >  	(sectors >> F2FS_LOG_SECTORS_PER_BLOCK)
> > -#define MAX_BIO_BLOCKS(sbi)						\
> > -	((int)min((int)max_hw_blocks(sbi), BIO_MAX_PAGES))
> >  
> >  /*
> >   * indicate a block allocation direction: RIGHT and LEFT.
> > @@ -698,13 +696,6 @@ static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
> >  	return false;
> >  }
> >  
> > -static inline unsigned int max_hw_blocks(struct f2fs_sb_info *sbi)
> > -{
> > -	struct block_device *bdev = sbi->sb->s_bdev;
> > -	struct request_queue *q = bdev_get_queue(bdev);
> > -	return SECTOR_TO_BLOCK(queue_max_sectors(q));
> > -}
> > -
> >  /*
> >   * It is very important to gather dirty pages and write at once, so that we can
> >   * submit a big bio without interfering other data writes.
> > @@ -722,7 +713,7 @@ static inline int nr_pages_to_skip(struct f2fs_sb_info *sbi, int type)
> >  	else if (type == NODE)
> >  		return 8 * sbi->blocks_per_seg;
> >  	else if (type == META)
> > -		return 8 * MAX_BIO_BLOCKS(sbi);
> > +		return 8 * BIO_MAX_PAGES;
> >  	else
> >  		return 0;
> >  }
> > @@ -739,11 +730,9 @@ static inline long nr_pages_to_write(struct f2fs_sb_info *sbi, int type,
> >  		return 0;
> >  
> >  	nr_to_write = wbc->nr_to_write;
> > -
> > +	desired = BIO_MAX_PAGES;
> >  	if (type == NODE)
> > -		desired = 2 * max_hw_blocks(sbi);
> > -	else
> > -		desired = MAX_BIO_BLOCKS(sbi);
> > +		desired <<= 1;
> >  
> >  	wbc->nr_to_write = desired;
> >  	return desired - nr_to_write;
> >