linux-kernel - Re: [PATCH 1/2] f2fs: flush dirty nat entries when exceeding threshold

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Date:	Sat, 16 Jan 2016 12:29:58 -0800
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] f2fs: flush dirty nat entries when exceeding
 threshold

Hi Chao,

On Sat, Jan 16, 2016 at 05:36:40PM +0800, Chao Yu wrote:
> When testing f2fs with xfstest, generic/251 is stuck for long time,
> the case uses below serials to obtain fresh released space in device,
> in order to preparing for following fstrim test.
> 
> 1. rm -rf /mnt/dir
> 2. mkdir /mnt/dir/
> 3. cp -axT `pwd`/ /mnt/dir/
> 4. goto 1
> 
> During preparing step, all nat entries will be cached in nat cache,
> most of them are dirty entries with invalid blkaddr, which means
> nodes related to these entries have been truncated, and they could
> be reused after the dirty entries been checkpointed.
> 
> However, there was no checkpoint been triggered, so nid allocators
> (e.g. mkdir, creat) will run into long journey of iterating all NAT
> pages, looking for free nids in alloc_nid->build_free_nids.
> 
> Here, we give another chance to f2fs_balance_fs_bg to do checkpoint
> to flush nat entries for reusing in free nid cache when dirty entry
> count exceeds 10% of max count.
> 
> Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> ---
>  fs/f2fs/node.h    | 8 ++++++++
>  fs/f2fs/segment.c | 3 ++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index d4d1f63..630c62d 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -25,6 +25,8 @@
>  /* control the memory footprint threshold (10MB per 1GB ram) */
>  #define DEF_RAM_THRESHOLD	10
>  
> +#define DEF_DIRTY_NAT_THRESHOLD		10	/* 10% over max nid */
> +
>  /* vector size for gang look-up from nat cache that consists of radix tree */
>  #define NATVEC_SIZE	64
>  #define SETVEC_SIZE	32
> @@ -117,6 +119,12 @@ static inline void raw_nat_from_node_info(struct f2fs_nat_entry *raw_ne,
>  	raw_ne->version = ni->version;
>  }
>  
> +static inline bool excess_dirty_nats(struct f2fs_sb_info *sbi)
> +{
> +	return NM_I(sbi)->dirty_nat_cnt >=
> +			NM_I(sbi)->max_nid * DEF_DIRTY_NAT_THRESHOLD / 100;

Need to add a sysfs entry?

Thanks,

> +}
> +
>  enum mem_type {
>  	FREE_NIDS,	/* indicates the free nid list */
>  	NAT_ENTRIES,	/* indicates the cached nat entry */
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 5904a41..68800e6 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -291,8 +291,9 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
>  
>  	/* checkpoint is the only way to shrink partial cached entries */
>  	if (!available_free_memory(sbi, NAT_ENTRIES) ||
> -			excess_prefree_segs(sbi) ||
>  			!available_free_memory(sbi, INO_ENTRIES) ||
> +			excess_prefree_segs(sbi) ||
> +			excess_dirty_nats(sbi) ||
>  			(is_idle(sbi) && f2fs_time_over(sbi, CP_TIME))) {
>  		if (test_opt(sbi, DATA_FLUSH))
>  			sync_dirty_inodes(sbi, FILE_INODE);
> -- 
> 2.6.3
>