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Date:   Fri, 25 Oct 2019 11:18:20 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: support aligned pinned file
Message-ID: <20191025181820.GA24183@jaegeuk-macbookpro.roam.corp.google.com>
References: <20191022171602.93637-1-jaegeuk@kernel.org>
 <c916c749-0abe-a7b7-e748-f0c4d5599e4a@huawei.com>
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On 10/24, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2019/10/23 1:16, Jaegeuk Kim wrote:
> > This patch supports 2MB-aligned pinned file, which can guarantee no GC at all
> > by allocating fully valid 2MB segment.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >  fs/f2fs/f2fs.h     |  4 +++-
> >  fs/f2fs/file.c     | 39 ++++++++++++++++++++++++++++++++++-----
> >  fs/f2fs/recovery.c |  2 +-
> >  fs/f2fs/segment.c  | 21 ++++++++++++++++++++-
> >  fs/f2fs/segment.h  |  2 ++
> >  fs/f2fs/super.c    |  1 +
> >  fs/f2fs/sysfs.c    |  2 ++
> >  7 files changed, 63 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index ca342f4c7db1..c681f51e351b 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -890,6 +890,7 @@ enum {
> >  	CURSEG_WARM_NODE,	/* direct node blocks of normal files */
> >  	CURSEG_COLD_NODE,	/* indirect node blocks */
> >  	NO_CHECK_TYPE,
> > +	CURSEG_COLD_DATA_PINNED,/* cold data for pinned file */
> >  };
> >  
> >  struct flush_cmd {
> > @@ -1301,6 +1302,7 @@ struct f2fs_sb_info {
> >  
> >  	/* threshold for gc trials on pinned files */
> >  	u64 gc_pin_file_threshold;
> > +	struct rw_semaphore pin_sem;
> >  
> >  	/* maximum # of trials to find a victim segment for SSR and GC */
> >  	unsigned int max_victim_search;
> > @@ -3116,7 +3118,7 @@ void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
> >  int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
> >  void allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type,
> >  					unsigned int start, unsigned int end);
> > -void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi);
> > +void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi, int type);
> >  int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range);
> >  bool f2fs_exist_trim_candidates(struct f2fs_sb_info *sbi,
> >  					struct cp_control *cpc);
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 29bc0a542759..f6c038e8a6a7 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1545,12 +1545,41 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
> >  	if (off_end)
> >  		map.m_len++;
> >  
> > -	if (f2fs_is_pinned_file(inode))
> > -		map.m_seg_type = CURSEG_COLD_DATA;
> > +	if (!map.m_len)
> > +		return 0;
> > +
> > +	if (f2fs_is_pinned_file(inode)) {
> > +		block_t len = (map.m_len >> sbi->log_blocks_per_seg) <<
> > +					sbi->log_blocks_per_seg;
> > +		block_t done = 0;
> > +
> > +		if (map.m_len % sbi->blocks_per_seg)
> > +			len += sbi->blocks_per_seg;
> >  
> > -	err = f2fs_map_blocks(inode, &map, 1, (f2fs_is_pinned_file(inode) ?
> > -						F2FS_GET_BLOCK_PRE_DIO :
> > -						F2FS_GET_BLOCK_PRE_AIO));
> > +		map.m_len = sbi->blocks_per_seg;
> > +next_alloc:
> > +		mutex_lock(&sbi->gc_mutex);
> > +		err = f2fs_gc(sbi, true, false, NULL_SEGNO);
> > +		if (err && err != -ENODATA && err != -EAGAIN)
> > +			goto out_err;
> 
> To grab enough free space?
> 
> Shouldn't we call
> 
> 	if (has_not_enough_free_secs(sbi, 0, 0)) {
> 		mutex_lock(&sbi->gc_mutex);
> 		f2fs_gc(sbi, false, false, NULL_SEGNO);
> 	}

The above calls gc all the time. Do we need this?

> 
> > +
> > +		down_write(&sbi->pin_sem);
> > +		map.m_seg_type = CURSEG_COLD_DATA_PINNED;
> > +		f2fs_allocate_new_segments(sbi, CURSEG_COLD_DATA);
> > +		err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_DIO);
> > +		up_write(&sbi->pin_sem);
> > +
> > +		done += map.m_len;
> > +		len -= map.m_len;
> > +		map.m_lblk += map.m_len;
> > +		if (!err && len)
> > +			goto next_alloc;
> > +
> > +		map.m_len = done;
> > +	} else {
> > +		err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
> > +	}
> > +out_err:
> >  	if (err) {
> >  		pgoff_t last_off;
> >  
> > diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
> > index 783773e4560d..76477f71d4ee 100644
> > --- a/fs/f2fs/recovery.c
> > +++ b/fs/f2fs/recovery.c
> > @@ -711,7 +711,7 @@ static int recover_data(struct f2fs_sb_info *sbi, struct list_head *inode_list,
> >  		f2fs_put_page(page, 1);
> >  	}
> >  	if (!err)
> > -		f2fs_allocate_new_segments(sbi);
> > +		f2fs_allocate_new_segments(sbi, NO_CHECK_TYPE);
> >  	return err;
> >  }
> >  
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 25c750cd0272..253d72c2663c 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -2690,7 +2690,7 @@ void allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type,
> >  	up_read(&SM_I(sbi)->curseg_lock);
> >  }
> >  
> > -void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi)
> > +void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi, int type)
> >  {
> >  	struct curseg_info *curseg;
> >  	unsigned int old_segno;
> > @@ -2699,6 +2699,9 @@ void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi)
> >  	down_write(&SIT_I(sbi)->sentry_lock);
> >  
> >  	for (i = CURSEG_HOT_DATA; i <= CURSEG_COLD_DATA; i++) {
> > +		if (type != NO_CHECK_TYPE && i != type)
> > +			continue;
> > +
> >  		curseg = CURSEG_I(sbi, i);
> >  		old_segno = curseg->segno;
> >  		SIT_I(sbi)->s_ops->allocate_segment(sbi, i, true);
> > @@ -3068,6 +3071,19 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
> >  {
> >  	struct sit_info *sit_i = SIT_I(sbi);
> >  	struct curseg_info *curseg = CURSEG_I(sbi, type);
> > +	bool put_pin_sem = false;
> > +
> > +	if (type == CURSEG_COLD_DATA) {
> > +		/* GC during CURSEG_COLD_DATA_PINNED allocation */
> > +		if (down_read_trylock(&sbi->pin_sem)) {
> > +			put_pin_sem = true;
> > +		} else {
> > +			type = CURSEG_WARM_DATA;
> > +			curseg = CURSEG_I(sbi, type);
> 
> It will mix pending cold data into warm area... rather than recovering curseg to
> write pointer of last cold segment?
> 
> I know maybe that fallocate aligned address could be corner case, but I guess
> there should be some better solutions can handle race case more effectively.
> 
> One solution could be: allocating a virtual log header to select free segment as
> 2m-aligned space target.

I thought about that, but concluded to avoid too much changes.

> 
> Thanks,
> 
> > +		}
> > +	} else if (type == CURSEG_COLD_DATA_PINNED) {
> > +		type = CURSEG_COLD_DATA;
> > +	}
> >  
> >  	down_read(&SM_I(sbi)->curseg_lock);
> >  
> > @@ -3133,6 +3149,9 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
> >  	mutex_unlock(&curseg->curseg_mutex);
> >  
> >  	up_read(&SM_I(sbi)->curseg_lock);
> > +
> > +	if (put_pin_sem)
> > +		up_read(&sbi->pin_sem);
> >  }
> >  
> >  static void update_device_state(struct f2fs_io_info *fio)
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index 325781a1ae4d..a95467b202ea 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -313,6 +313,8 @@ struct sit_entry_set {
> >   */
> >  static inline struct curseg_info *CURSEG_I(struct f2fs_sb_info *sbi, int type)
> >  {
> > +	if (type == CURSEG_COLD_DATA_PINNED)
> > +		type = CURSEG_COLD_DATA;
> >  	return (struct curseg_info *)(SM_I(sbi)->curseg_array + type);
> >  }
> >  
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index f320fd11db48..c02a47ce551b 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -2853,6 +2853,7 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
> >  	spin_lock_init(&sbi->dev_lock);
> >  
> >  	init_rwsem(&sbi->sb_lock);
> > +	init_rwsem(&sbi->pin_sem);
> >  }
> >  
> >  static int init_percpu_info(struct f2fs_sb_info *sbi)
> > diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> > index b558b64a4c9c..f164959e4224 100644
> > --- a/fs/f2fs/sysfs.c
> > +++ b/fs/f2fs/sysfs.c
> > @@ -154,6 +154,8 @@ static ssize_t features_show(struct f2fs_attr *a,
> >  	if (f2fs_sb_has_casefold(sbi))
> >  		len += snprintf(buf + len, PAGE_SIZE - len, "%s%s",
> >  				len ? ", " : "", "casefold");
> > +	len += snprintf(buf + len, PAGE_SIZE - len, "%s%s",
> > +				len ? ", " : "", "pin_file");
> >  	len += snprintf(buf + len, PAGE_SIZE - len, "\n");
> >  	return len;
> >  }
> >