Re: [PATCH v2 04/18] nfsd: add a new struct file caching facility to nfsd

[Kinglong Mee <kinglongmee@gmail.com>]

On 8/6/2015 05:13, Jeff Layton wrote:
> Currently, NFSv2/3 reads and writes have to open a file, do the read or
> write and then close it again for each RPC. This is highly inefficient,
> especially when the underlying filesystem has a relatively slow open
> routine.
> 
> This patch adds a new open file cache to knfsd. Rather than doing an
> open for each RPC, the read/write handlers can call into this cache to
> see if there is one already there for the correct filehandle and
> NFS_MAY_READ/WRITE flags.
> 
> If there isn't an entry, then we create a new one and attempt to
> perform the open. If there is, then we wait until the entry is fully
> instantiated and return it if it is at the end of the wait. If it's
> not, then we attempt to take over construction.
> 
> Since the main goal is to speed up NFSv2/3 I/O, we don't want to
> close these files on last put of these objects. We need to keep them
> around for a little while since we never know when the next READ/WRITE
> will come in.
> 
> Cache entries have a hardcoded 1s timeout, and we have a recurring
> workqueue job that walks the cache and purges any entries that have
> expired.
> 
> Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
... snip ... 
> diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> index 9051ee54faa3..adf7e78b8e43 100644
> --- a/fs/nfsd/filecache.h
> +++ b/fs/nfsd/filecache.h
> @@ -4,6 +4,7 @@
>  #include <linux/jhash.h>
>  #include <linux/sunrpc/xdr.h>
>  
> +#include "nfsfh.h"
>  #include "export.h"
>  
>  /* hash table for nfs4_file */
> @@ -22,4 +23,24 @@ file_hashval(struct knfsd_fh *fh)
>  	return nfsd_fh_hashval(fh) & (NFSD_FILE_HASH_SIZE - 1);
>  }
>  
> +struct nfsd_file {

There is a nfs4_file in nfsd, it's not easy to distinguish them for a new folk.
More comments or a meaningful name is better.

> +	struct hlist_node	nf_node;
> +	struct list_head	nf_dispose;
> +	struct rcu_head		nf_rcu;
> +	struct file		*nf_file;
> +	unsigned long		nf_time;
> +#define NFSD_FILE_HASHED	(0)

Why not using hlist_unhashed()? 

thanks,
Kinglong Mee

> +#define NFSD_FILE_PENDING	(1)
> +	unsigned long		nf_flags;
> +	struct knfsd_fh		nf_handle;
> +	unsigned int		nf_hashval;
> +	atomic_t		nf_ref;
> +	unsigned char		nf_may;
> +};
> +
> +int nfsd_file_cache_init(void);
> +void nfsd_file_cache_shutdown(void);
> +void nfsd_file_put(struct nfsd_file *nf);
> +__be32 nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> +		  unsigned int may_flags, struct nfsd_file **nfp);
>  #endif /* _FS_NFSD_FILECACHE_H */
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index ced9944201a0..0572441e23ec 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -23,6 +23,7 @@
>  #include "cache.h"
>  #include "vfs.h"
>  #include "netns.h"
> +#include "filecache.h"
>  
>  #define NFSDDBG_FACILITY	NFSDDBG_SVC
>  
> @@ -233,11 +234,17 @@ static int nfsd_startup_generic(int nrservs)
>  	if (!nfsd_laundry_wq)
>  		goto out_racache;
>  
> -	ret = nfs4_state_start();
> +	ret = nfsd_file_cache_init();
>  	if (ret)
>  		goto out_wq;
> +
> +	ret = nfs4_state_start();
> +	if (ret)
> +		goto out_nfsd_file;
>  	return 0;
>  
> +out_nfsd_file:
> +	nfsd_file_cache_shutdown();
>  out_wq:
>  	destroy_workqueue(nfsd_laundry_wq);
>  	nfsd_laundry_wq = NULL;
> @@ -254,6 +261,7 @@ static void nfsd_shutdown_generic(void)
>  		return;
>  
>  	nfs4_state_shutdown();
> +	nfsd_file_cache_shutdown();
>  	nfsd_racache_shutdown();
>  }
>  
>