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Date:   Wed, 6 May 2020 08:05:21 -0700
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 v2] f2fs: shrink spinlock coverage

On 05/06, Chao Yu wrote:
> In f2fs_try_to_free_nids(), .nid_list_lock spinlock critical region will
> increase as expected shrink number increase, to avoid spining other CPUs
> for long time, it's better to implement like extent cache and nats
> shrinker.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
> v2:
> - fix unlock wrong spinlock.
>  fs/f2fs/node.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 4da0d8713df5..ad0b14f4dab8 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -2488,7 +2488,6 @@ void f2fs_alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
>  int f2fs_try_to_free_nids(struct f2fs_sb_info *sbi, int nr_shrink)
>  {
>  	struct f2fs_nm_info *nm_i = NM_I(sbi);
> -	struct free_nid *i, *next;
>  	int nr = nr_shrink;
>  
>  	if (nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> @@ -2498,14 +2497,22 @@ int f2fs_try_to_free_nids(struct f2fs_sb_info *sbi, int nr_shrink)
>  		return 0;
>  
>  	spin_lock(&nm_i->nid_list_lock);
> -	list_for_each_entry_safe(i, next, &nm_i->free_nid_list, list) {
> -		if (nr_shrink <= 0 ||
> -				nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> +	while (nr_shrink) {
> +		struct free_nid *i;
> +
> +		if (nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
>  			break;
>  
> +		i = list_first_entry(&nm_i->free_nid_list,
> +					struct free_nid, list);
> +		list_del(&i->list);
> +		spin_unlock(&nm_i->nid_list_lock);
> +
>  		__remove_free_nid(sbi, i, FREE_NID);

__remove_free_nid() will do list_del again. btw, how about just splitting out
given nr_shrink into multiple trials?

>  		kmem_cache_free(free_nid_slab, i);
>  		nr_shrink--;
> +
> +		spin_lock(&nm_i->nid_list_lock);
>  	}
>  	spin_unlock(&nm_i->nid_list_lock);
>  	mutex_unlock(&nm_i->build_lock);
> -- 
> 2.18.0.rc1

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