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Date:   Wed, 16 Nov 2016 19:31:45 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH v3] f2fs: don't wait writeback for datas during checkpoint

On Thu, Nov 17, 2016 at 11:06:09AM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2016/11/17 3:18, Jaegeuk Kim wrote:
> > Hi Chao,
> > 
> > On Wed, Nov 16, 2016 at 10:41:20AM +0800, Chao Yu wrote:
> >> Normally, while committing checkpoint, we will wait on all pages to be
> >> writebacked no matter the page is data or metadata, so in scenario where
> >> there are lots of data IO being submitted with metadata, we may suffer
> >> long latency for waiting writeback during checkpoint.
> >>
> >> Indeed, we only care about persistence for pages with metadata, but not
> >> pages with data, as file system consistent are only related to metadate,
> >> so in order to avoid encountering long latency in above scenario, let's
> >> recognize and reference metadata in submitted IOs, wait writeback only
> >> for metadatas.
> >>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >> v3: clean up codes as Jaegeuk suggested.
> >>  fs/f2fs/checkpoint.c |  2 +-
> >>  fs/f2fs/data.c       | 37 +++++++++++++++++++++++++++++++------
> >>  fs/f2fs/debug.c      |  7 ++++---
> >>  fs/f2fs/f2fs.h       |  8 +++++---
> >>  fs/f2fs/file.c       |  2 --
> >>  fs/f2fs/gc.c         |  2 --
> >>  fs/f2fs/segment.c    |  1 -
> >>  7 files changed, 41 insertions(+), 18 deletions(-)
> >>
> >> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >> index 7bece59..5039ed8 100644
> >> --- a/fs/f2fs/checkpoint.c
> >> +++ b/fs/f2fs/checkpoint.c
> >> @@ -1003,7 +1003,7 @@ static void wait_on_all_pages_writeback(struct f2fs_sb_info *sbi)
> >>  	for (;;) {
> >>  		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
> >>  
> >> -		if (!atomic_read(&sbi->nr_wb_bios))
> >> +		if (!get_pages(sbi, F2FS_WB_CP_DATA))
> >>  			break;
> >>  
> >>  		io_schedule_timeout(5*HZ);
> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >> index 66d2aee..4115689 100644
> >> --- a/fs/f2fs/data.c
> >> +++ b/fs/f2fs/data.c
> >> @@ -29,6 +29,28 @@
> >>  #include "trace.h"
> >>  #include <trace/events/f2fs.h>
> >>  
> >> +static bool __is_cp_guaranteed(struct page *page)
> >> +{
> >> +	struct address_space *mapping = page->mapping;
> >> +	struct inode *inode;
> >> +	struct f2fs_sb_info *sbi;
> >> +
> >> +	if (!mapping)
> >> +		return false;
> >> +
> >> +	inode = mapping->host;
> >> +	sbi = F2FS_I_SB(inode);
> >> +
> >> +	if (inode->i_ino == F2FS_META_INO(sbi) ||
> >> +			inode->i_ino ==  F2FS_NODE_INO(sbi) ||
> >> +			S_ISDIR(inode->i_mode) ||
> >> +			is_cold_data(page))
> >> +		return true;
> >> +	return false;
> >> +}
> >> +
> >> +#define WB_DATA_TYPE(p)	(__is_cp_guaranteed(p) ? F2FS_WB_CP_DATA : F2FS_WB_DATA)
> > 
> > I moved this into f2fs.h.
> 
> Indeed, I wanted to, but it looks that they are invoked only in data.c, and
> f2fs.h grows bigger and bigger, so I keep it in data.c. Anyway, agree and thanks
> for the cleanup.
> 
> How do you think of letting me clean up f2fs.h by split *.c related macros and
> function in f2fs.h into *.h (data.h extent.h...)?

Hmm, IMO, current f2fs.h would be fine, since f2fs-tools can use this.

Thanks,

> 
> Thanks,
> 
> > 
> > Thanks,
> > 
> >> +
> >>  static void f2fs_read_end_io(struct bio *bio)
> >>  {
> >>  	struct bio_vec *bvec;
> >> @@ -73,6 +95,7 @@ static void f2fs_write_end_io(struct bio *bio)
> >>  
> >>  	bio_for_each_segment_all(bvec, bio, i) {
> >>  		struct page *page = bvec->bv_page;
> >> +		enum count_type type = WB_DATA_TYPE(page);
> >>  
> >>  		fscrypt_pullback_bio_page(&page, true);
> >>  
> >> @@ -80,9 +103,11 @@ static void f2fs_write_end_io(struct bio *bio)
> >>  			mapping_set_error(page->mapping, -EIO);
> >>  			f2fs_stop_checkpoint(sbi, true);
> >>  		}
> >> +		dec_page_count(sbi, type);
> >> +		clear_cold_data(page);
> >>  		end_page_writeback(page);
> >>  	}
> >> -	if (atomic_dec_and_test(&sbi->nr_wb_bios) &&
> >> +	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> >>  				wq_has_sleeper(&sbi->cp_wait))
> >>  		wake_up(&sbi->cp_wait);
> >>  
> >> @@ -111,7 +136,6 @@ static inline void __submit_bio(struct f2fs_sb_info *sbi,
> >>  				struct bio *bio, enum page_type type)
> >>  {
> >>  	if (!is_read_io(bio_op(bio))) {
> >> -		atomic_inc(&sbi->nr_wb_bios);
> >>  		if (f2fs_sb_mounted_blkzoned(sbi->sb) &&
> >>  			current->plug && (type == DATA || type == NODE))
> >>  			blk_finish_plug(current->plug);
> >> @@ -272,6 +296,11 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
> >>  		verify_block_addr(sbi, fio->old_blkaddr);
> >>  	verify_block_addr(sbi, fio->new_blkaddr);
> >>  
> >> +	bio_page = fio->encrypted_page ? fio->encrypted_page : fio->page;
> >> +
> >> +	if (!is_read)
> >> +		inc_page_count(sbi, WB_DATA_TYPE(bio_page));
> >> +
> >>  	down_write(&io->io_rwsem);
> >>  
> >>  	if (io->bio && (io->last_block_in_bio != fio->new_blkaddr - 1 ||
> >> @@ -284,8 +313,6 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
> >>  		io->fio = *fio;
> >>  	}
> >>  
> >> -	bio_page = fio->encrypted_page ? fio->encrypted_page : fio->page;
> >> -
> >>  	if (bio_add_page(io->bio, bio_page, PAGE_SIZE, 0) <
> >>  							PAGE_SIZE) {
> >>  		__submit_merged_bio(io);
> >> @@ -1296,7 +1323,6 @@ static int f2fs_write_data_page(struct page *page,
> >>  	if (err && err != -ENOENT)
> >>  		goto redirty_out;
> >>  
> >> -	clear_cold_data(page);
> >>  out:
> >>  	inode_dec_dirty_pages(inode);
> >>  	if (err)
> >> @@ -1699,7 +1725,6 @@ static int f2fs_write_end(struct file *file,
> >>  		goto unlock_out;
> >>  
> >>  	set_page_dirty(page);
> >> -	clear_cold_data(page);
> >>  
> >>  	if (pos + copied > i_size_read(inode))
> >>  		f2fs_i_size_write(inode, pos + copied);
> >> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> >> index 2fdf233..67a04d8 100644
> >> --- a/fs/f2fs/debug.c
> >> +++ b/fs/f2fs/debug.c
> >> @@ -50,7 +50,8 @@ static void update_general_status(struct f2fs_sb_info *sbi)
> >>  	si->ndirty_files = sbi->ndirty_inode[FILE_INODE];
> >>  	si->ndirty_all = sbi->ndirty_inode[DIRTY_META];
> >>  	si->inmem_pages = get_pages(sbi, F2FS_INMEM_PAGES);
> >> -	si->wb_bios = atomic_read(&sbi->nr_wb_bios);
> >> +	si->nr_wb_cp_data = get_pages(sbi, F2FS_WB_CP_DATA);
> >> +	si->nr_wb_data = get_pages(sbi, F2FS_WB_DATA);
> >>  	si->total_count = (int)sbi->user_block_count / sbi->blocks_per_seg;
> >>  	si->rsvd_segs = reserved_segments(sbi);
> >>  	si->overp_segs = overprovision_segments(sbi);
> >> @@ -313,8 +314,8 @@ static int stat_show(struct seq_file *s, void *v)
> >>  		seq_printf(s, "  - Inner Struct Count: tree: %d(%d), node: %d\n",
> >>  				si->ext_tree, si->zombie_tree, si->ext_node);
> >>  		seq_puts(s, "\nBalancing F2FS Async:\n");
> >> -		seq_printf(s, "  - inmem: %4d, wb_bios: %4d\n",
> >> -			   si->inmem_pages, si->wb_bios);
> >> +		seq_printf(s, "  - inmem: %4d, wb_cp_data: %4d, wb_data: %4d\n",
> >> +			   si->inmem_pages, si->nr_wb_cp_data, si->nr_wb_data);
> >>  		seq_printf(s, "  - nodes: %4d in %4d\n",
> >>  			   si->ndirty_node, si->node_pages);
> >>  		seq_printf(s, "  - dents: %4d in dirs:%4d (%4d)\n",
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >> index f264c1b..34405dc 100644
> >> --- a/fs/f2fs/f2fs.h
> >> +++ b/fs/f2fs/f2fs.h
> >> @@ -682,6 +682,8 @@ enum count_type {
> >>  	F2FS_DIRTY_META,
> >>  	F2FS_INMEM_PAGES,
> >>  	F2FS_DIRTY_IMETA,
> >> +	F2FS_WB_CP_DATA,
> >> +	F2FS_WB_DATA,
> >>  	NR_COUNT_TYPE,
> >>  };
> >>  
> >> @@ -849,7 +851,6 @@ struct f2fs_sb_info {
> >>  	block_t discard_blks;			/* discard command candidats */
> >>  	block_t last_valid_block_count;		/* for recovery */
> >>  	u32 s_next_generation;			/* for NFS support */
> >> -	atomic_t nr_wb_bios;			/* # of writeback bios */
> >>  
> >>  	/* # of pages, see count_type */
> >>  	atomic_t nr_pages[NR_COUNT_TYPE];
> >> @@ -1263,7 +1264,8 @@ static inline void inc_page_count(struct f2fs_sb_info *sbi, int count_type)
> >>  {
> >>  	atomic_inc(&sbi->nr_pages[count_type]);
> >>  
> >> -	if (count_type == F2FS_DIRTY_DATA || count_type == F2FS_INMEM_PAGES)
> >> +	if (count_type == F2FS_DIRTY_DATA || count_type == F2FS_INMEM_PAGES ||
> >> +		count_type == F2FS_WB_CP_DATA || count_type == F2FS_WB_DATA)
> >>  		return;
> >>  
> >>  	set_sbi_flag(sbi, SBI_IS_DIRTY);
> >> @@ -2219,7 +2221,7 @@ struct f2fs_stat_info {
> >>  	unsigned int ndirty_dirs, ndirty_files, ndirty_all;
> >>  	int nats, dirty_nats, sits, dirty_sits, free_nids, alloc_nids;
> >>  	int total_count, utilization;
> >> -	int bg_gc, wb_bios;
> >> +	int bg_gc, nr_wb_cp_data, nr_wb_data;
> >>  	int inline_xattr, inline_inode, inline_dir, orphans;
> >>  	unsigned int valid_count, valid_node_count, valid_inode_count, discard_blks;
> >>  	unsigned int bimodal, avg_vblocks;
> >> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >> index e821c39..dd1c5c3 100644
> >> --- a/fs/f2fs/file.c
> >> +++ b/fs/f2fs/file.c
> >> @@ -96,8 +96,6 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
> >>  	if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
> >>  		f2fs_wait_on_encrypted_page_writeback(sbi, dn.data_blkaddr);
> >>  
> >> -	/* if gced page is attached, don't write to cold segment */
> >> -	clear_cold_data(page);
> >>  out:
> >>  	sb_end_pagefault(inode->i_sb);
> >>  	f2fs_update_time(sbi, REQ_TIME);
> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index 11ff05e..c4b3c32 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -695,8 +695,6 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
> >>  			congestion_wait(BLK_RW_ASYNC, HZ/50);
> >>  			goto retry;
> >>  		}
> >> -
> >> -		clear_cold_data(page);
> >>  	}
> >>  out:
> >>  	f2fs_put_page(page, 1);
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index 078c571..d8aa703 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -290,7 +290,6 @@ static int __commit_inmem_pages(struct inode *inode,
> >>  			/* record old blkaddr for revoking */
> >>  			cur->old_addr = fio.old_blkaddr;
> >>  
> >> -			clear_cold_data(page);
> >>  			submit_bio = true;
> >>  		}
> >>  		unlock_page(page);
> >> -- 
> >> 2.8.2.311.gee88674
> > 
> > .
> > 

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