netdev - Re: [PATCH v3 16/32] NFSD: Fix the filecache LRU shrinker

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Date:   Fri, 08 Jul 2022 15:37:05 -0400
From:   Jeff Layton <jlayton@...hat.com>
To:     Chuck Lever <chuck.lever@...cle.com>, linux-nfs@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     david@...morbit.com, tgraf@...g.ch
Subject: Re: [PATCH v3 16/32] NFSD: Fix the filecache LRU shrinker

On Fri, 2022-07-08 at 14:25 -0400, Chuck Lever wrote:
> Without LRU item rotation, the shrinker visits only a few items on
> the end of the LRU list, and those would always be long-term OPEN
> files for NFSv4 workloads. That makes the filecache shrinker
> completely ineffective.
> 
> Adopt the same strategy as the inode LRU by using LRU_ROTATE.
> 
> Suggested-by: Dave Chinner <david@...morbit.com>
> Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
> ---
>  fs/nfsd/filecache.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 6e9e186334ab..bd6ba63f69ae 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -452,6 +452,7 @@ nfsd_file_dispose_list_delayed(struct list_head *dispose)
>   *
>   * Return values:
>   *   %LRU_REMOVED: @item was removed from the LRU
> + *   %LRU_ROTATED: @item is to be moved to the LRU tail

%LRU_ROTATE

>   *   %LRU_SKIP: @item cannot be evicted
>   */
>  static enum lru_status
> @@ -490,7 +491,7 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru,
>  
>  	if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags)) {
>  		trace_nfsd_file_gc_referenced(nf);
> -		return LRU_SKIP;
> +		return LRU_ROTATE;
>  	}
>  
>  	if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
> @@ -532,7 +533,7 @@ nfsd_file_gc(void)
>  	unsigned long ret;
>  
>  	ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb,
> -			    &dispose, LONG_MAX);
> +			    &dispose, list_lru_count(&nfsd_file_lru));
>  	trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru));
>  	nfsd_file_gc_dispose_list(&dispose);
>  }
> 
> 

-- 
Jeff Layton <jlayton@...hat.com>