Re: [PATCH v2] f2fs: don't wait writeback for datas during checkpoint

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Chao,

On Tue, Nov 15, 2016 at 07:33:27PM +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@huawei.com>
> ---
> v2: cover GC + CP + sudden power-off case.
>  fs/f2fs/checkpoint.c |  2 +-
>  fs/f2fs/data.c       | 41 +++++++++++++++++++++++++++++++++++------
>  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, 45 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 7bece59..bdf8a50 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_META))
>  			break;
>  
>  		io_schedule_timeout(5*HZ);
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 66d2aee..e9b9d0f 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -22,6 +22,7 @@
>  #include <linux/mm.h>
>  #include <linux/memcontrol.h>
>  #include <linux/cleancache.h>
> +#include <linux/fscrypto.h>
>  
>  #include "f2fs.h"
>  #include "node.h"
> @@ -29,6 +30,30 @@
>  #include "trace.h"
>  #include <trace/events/f2fs.h>
>  
> +static bool f2fs_is_meta_data(struct page *page, bool clear_cold)

So, we'd better change the names to make all these clear.
How about?

	__is_cp_guaranteed() ?

> +{
> +	struct address_space *mapping = page->mapping;
> +	struct inode *inode;
> +	struct f2fs_sb_info *sbi;
> +	bool is_cold;
> +
> +	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) ||

			is_cold_data(page) ||

> +			S_ISDIR(inode->i_mode))
> +		return true;
> +
> +	is_cold = is_cold_data(page);
> +	if (is_cold && clear_cold)
> +		clear_cold_data(page);

It looks an inappropriate place to do this. How about doing clear_cold_data()
out of this function in end_io.

> +	return is_cold;
> +}
> +
>  static void f2fs_read_end_io(struct bio *bio)
>  {
>  	struct bio_vec *bvec;
> @@ -73,6 +98,7 @@ static void f2fs_write_end_io(struct bio *bio)
>  
>  	bio_for_each_segment_all(bvec, bio, i) {
>  		struct page *page = bvec->bv_page;
> +		bool is_meta = f2fs_is_meta_data(page, true);
>  
>  		fscrypt_pullback_bio_page(&page, true);
>  
> @@ -80,9 +106,10 @@ static void f2fs_write_end_io(struct bio *bio)
>  			mapping_set_error(page->mapping, -EIO);
>  			f2fs_stop_checkpoint(sbi, true);
>  		}
> +		dec_page_count(sbi, is_meta ? F2FS_WB_META : F2FS_WB_DATA);


#define WB_DATA_TYPE(p)	(__is_cp_guaranteed(p) ? F2FS_WB_CP_DATA : F2FS_WB_DATA)

		dec_page_count(sbi, WB_DATA_TYPE(page));
		clear_cold_data(page);

>  		end_page_writeback(page);
>  	}
> -	if (atomic_dec_and_test(&sbi->nr_wb_bios) &&
> +	if (!get_pages(sbi, F2FS_WB_META) &&

	F2FS_WB_CP_DATA

>  				wq_has_sleeper(&sbi->cp_wait))
>  		wake_up(&sbi->cp_wait);
>  
> @@ -111,7 +138,6 @@ 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 +298,13 @@ 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) {
> +		bool is_meta = f2fs_is_meta_data(bio_page, false);
> +		inc_page_count(sbi, is_meta ? F2FS_WB_META : F2FS_WB_DATA);

		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 +317,6 @@ 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 +1327,6 @@ 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 +1729,6 @@ 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..f2d87de 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_meta = get_pages(sbi, F2FS_WB_META);
> +	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_meta: %4d, wb_data: %4d\n",
> +			   si->inmem_pages, si->nr_wb_meta, 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..f440848 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_META,

	F2FS_WB_CP_DATA,

Thanks,

> +	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_META || 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_meta, 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