linux-kernel - Re: [PATCH] NFS: Correct timing for assigning access cache timestamp

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Date:   Wed, 08 Mar 2023 09:45:37 -0500
From:   Benjamin Coddington <bcodding@...hat.com>
To:     Chengen Du <chengen.du@...onical.com>
Cc:     trond.myklebust@...merspace.com, anna@...nel.org,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS: Correct timing for assigning access cache timestamp

On 8 Mar 2023, at 3:03, Chengen Du wrote:

> When the user's login time is newer than the cache's timestamp,
> the original entry in the RB-tree will be replaced by a new entry.
> Currently, the timestamp is only set if the entry is not found in
> the RB-tree, which can cause the timestamp to be undefined when
> the entry exists. This may result in a significant increase in
> ACCESS operations if the timestamp is set to zero.
>
> Signed-off-by: Chengen Du <chengen.du@...onical.com>
> ---
>  fs/nfs/dir.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index a41c3ee4549c..6fbcbb8d6587 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -3089,7 +3089,6 @@ static void nfs_access_add_rbtree(struct inode *inode,
>  		else
>  			goto found;
>  	}
> -	set->timestamp = ktime_get_ns();
>  	rb_link_node(&set->rb_node, parent, p);
>  	rb_insert_color(&set->rb_node, root_node);
>  	list_add_tail(&set->lru, &nfsi->access_cache_entry_lru);
> @@ -3114,6 +3113,7 @@ void nfs_access_add_cache(struct inode *inode, struct nfs_access_entry *set,
>  	cache->fsgid = cred->fsgid;
>  	cache->group_info = get_group_info(cred->group_info);
>  	cache->mask = set->mask;
> +	cache->timestamp = ktime_get_ns();
>
>  	/* The above field assignments must be visible
>  	 * before this item appears on the lru.  We cannot easily
> -- 
> 2.37.2

Looks good to me.

Reviewed-by: Benjamin Coddington <bcodding@...hat.com>