linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: avoid down_write on nat_tree

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Date:   Sun, 19 Dec 2021 16:53:57 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: avoid down_write on nat_tree_lock
 during checkpoint

On 2021/12/15 2:24, Jaegeuk Kim wrote:
> Let's cache nat entry if there's no lock contention only.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>   fs/f2fs/node.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 556fcd8457f3..b1bc7d76da3b 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -430,6 +430,10 @@ static void cache_nat_entry(struct f2fs_sb_info *sbi, nid_t nid,
>   	struct f2fs_nm_info *nm_i = NM_I(sbi);
>   	struct nat_entry *new, *e;
>   
> +	/* Let's mitigate lock contention of nat_tree_lock during checkpoint */
> +	if (rwsem_is_locked(&sbi->cp_global_sem))

Why not down_write_trylock(nat_tree_lock)? cp_global_sem lock coverage is larger than
nat_tree_lock's in f2fs_write_checkpoint().

Thanks,

> +		return;
> +
>   	new = __alloc_nat_entry(sbi, nid, false);
>   	if (!new)
>   		return;