Re: [pnfs] [PATCH 2/5] nfsd41: change from page to memory based drc limits

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Jun 24, 2009 at 03:37:46PM -0400, andros@netapp.com wrote:
> From: Andy Adamson <andros@netapp.com>
> 
> NFSD_SLOT_CACHE_SIZE is the size of all encoded operation responses (excluding
> the sequence operation) that we want to cache.
> 
> Adjust NFSD_DRC_SIZE_SHIFT to reflect using 512 bytes instead of PAGE_SIZE.
> 
> Signed-off-by: Andy Adamson <andros@netapp.com>
> ---
>  fs/nfsd/nfs4state.c        |   30 ++++++++++++++----------------
>  fs/nfsd/nfssvc.c           |   17 +++++++++--------
>  include/linux/nfsd/nfsd.h  |    4 ++--
>  include/linux/nfsd/state.h |    1 +
>  4 files changed, 26 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 2e6a44e..b4a536d 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -414,35 +414,33 @@ gen_sessionid(struct nfsd4_session *ses)
>  
>  /*
>   * Give the client the number of slots it requests bound by
> - * NFSD_MAX_SLOTS_PER_SESSION and by sv_drc_max_pages.
> + * NFSD_MAX_SLOTS_PER_SESSION and by nfsd_drc_max_mem.
>   *
> - * If we run out of pages (sv_drc_pages_used == sv_drc_max_pages) we
> - * should (up to a point) re-negotiate active sessions and reduce their
> - * slot usage to make rooom for new connections. For now we just fail the
> - * create session.
> + * If we run out of reserved DRC memory we should (up to a point) re-negotiate
> + * active sessions and reduce their slot usage to make rooom for new
> + * connections. For now we just fail the create session.
>   */
>  static int set_forechannel_maxreqs(struct nfsd4_channel_attrs *fchan)
>  {
> -	int status = 0, np = fchan->maxreqs * NFSD_PAGES_PER_SLOT;
> +	int mem;
>  
>  	if (fchan->maxreqs < 1)
>  		return nfserr_inval;
>  	else if (fchan->maxreqs > NFSD_MAX_SLOTS_PER_SESSION)
>  		fchan->maxreqs = NFSD_MAX_SLOTS_PER_SESSION;
>  
> +	mem = fchan->maxreqs * NFSD_SLOT_CACHE_SIZE;
> +
>  	spin_lock(&nfsd_drc_lock);
> -	if (np + nfsd_drc_pages_used > nfsd_drc_max_pages)
> -		np = nfsd_drc_max_pages - nfsd_drc_pages_used;
> -	nfsd_drc_pages_used += np;
> +	if (mem + nfsd_drc_mem_used > nfsd_drc_max_mem)
> +		mem = nfsd_drc_max_mem - nfsd_drc_mem_used;
> +	nfsd_drc_mem_used += mem;

There's a small bug here: in the case where

	0 < mem < NFSD_PAGES_PER_SLOT,

we add mem into nfsd_drc_mem_used, but never subtract it back off.

>  	spin_unlock(&nfsd_drc_lock);
>  
> -	if (np <= 0) {
> -		status = nfserr_resource;
> -		fchan->maxreqs = 0;
> -	} else
> -		fchan->maxreqs = np / NFSD_PAGES_PER_SLOT;
> -
> -	return status;
> +	fchan->maxreqs = mem / NFSD_SLOT_CACHE_SIZE;
> +	if (fchan->maxreqs == 0)
> +		return nfserr_resource;
> +	return 0;
>  }
>  
>  /*
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index 78d8fcd..1793dba 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -74,8 +74,8 @@ struct svc_serv 		*nfsd_serv;
>   * nfsd_drc_pages_used tracks the current version 4.1 DRC memory usage.
>   */
>  spinlock_t	nfsd_drc_lock;
> -unsigned int	nfsd_drc_max_pages;
> -unsigned int	nfsd_drc_pages_used;
> +unsigned int	nfsd_drc_max_mem;
> +unsigned int	nfsd_drc_mem_used;
>  
>  #if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
>  static struct svc_stat	nfsd_acl_svcstats;
> @@ -247,13 +247,14 @@ void nfsd_reset_versions(void)
>  static void set_max_drc(void)
>  {
>  	/* The percent of nr_free_buffer_pages used by the V4.1 server DRC */
> -	#define NFSD_DRC_SIZE_SHIFT	7
> -	nfsd_drc_max_pages = nr_free_buffer_pages()
> -						>> NFSD_DRC_SIZE_SHIFT;
> -	nfsd_drc_pages_used = 0;
> +	#define NFSD_DRC_SIZE_SHIFT	10
> +	nfsd_drc_max_mem = (nr_free_buffer_pages()
> +					>> NFSD_DRC_SIZE_SHIFT) * PAGE_SIZE;
> +	nfsd_drc_mem_used = 0;
>  	spin_lock_init(&nfsd_drc_lock);
> -	dprintk("%s nfsd_drc_max_pages %u\n", __func__,
> -		nfsd_drc_max_pages);
> +	dprintk("%s nfsd_drc_max_mem %u [in pages %lu]\n", __func__,
> +		nfsd_drc_max_mem,
> +		nfsd_drc_max_mem / PAGE_SIZE);

The reader can do the "in pages" for him/herself if necessary.

>  }
>  
>  int nfsd_create_serv(void)
> diff --git a/include/linux/nfsd/nfsd.h b/include/linux/nfsd/nfsd.h
> index 2571f85..2812ed5 100644
> --- a/include/linux/nfsd/nfsd.h
> +++ b/include/linux/nfsd/nfsd.h
> @@ -57,8 +57,8 @@ extern u32			nfsd_supported_minorversion;
>  extern struct mutex		nfsd_mutex;
>  extern struct svc_serv		*nfsd_serv;
>  extern spinlock_t		nfsd_drc_lock;
> -extern unsigned int		nfsd_drc_max_pages;
> -extern unsigned int		nfsd_drc_pages_used;
> +extern unsigned int		nfsd_drc_max_mem;
> +extern unsigned int		nfsd_drc_mem_used;
>  
>  extern struct seq_operations nfs_exports_op;
>  
> diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
> index f5a95fd..10b6b30 100644
> --- a/include/linux/nfsd/state.h
> +++ b/include/linux/nfsd/state.h
> @@ -98,6 +98,7 @@ struct nfs4_cb_conn {
>  /* Maximum number of pages per slot cache entry */
>  #define NFSD_PAGES_PER_SLOT	1
>  /* Maximum number of operations per session compound */
> +#define NFSD_SLOT_CACHE_SIZE		512

Whoops--the above comment's misplaced now.

Also, this patch leaves the code in an inconsistent state where some
places still uses page size, others don't.  (E.g. we promise to cache
page_size, and still will, I think, and allocate that much, but we
calculate the maximum requests by the new smaller 512 byte value.)

Either fix all that at once, or just keep NFSD_SLOT_CACHE_SIZE 4k for
now.

--b.

>  #define NFSD_MAX_OPS_PER_COMPOUND	16
>  
>  struct nfsd4_cache_entry {
> -- 
> 1.5.4.3
> 
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