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Date:	Tue, 12 Feb 2008 17:10:31 -0700
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Jackson <pj@....com>,
	Christoph Lameter <clameter@....com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] mempolicy: convert MPOL constants to enum

On Mon, 2008-02-11 at 07:30 -0800, David Rientjes wrote: 
> The mempolicy mode constants, MPOL_DEFAULT, MPOL_PREFERRED, MPOL_BIND,
> and MPOL_INTERLEAVE, are better declared as part of an enum for type
> checking.
> 
> The policy member of struct mempolicy is also converted from type short
> to type unsigned short.  A negative policy does not have any legitimate
> meaning, so it is possible to change its type in preparation for adding
> optional mode flags later.
> 
> The equivalent member of struct shmem_sb_info is also changed from int
> to unsigned short.
> 
> For compatibility, the policy formal to get_mempolicy() remains as a
> pointer to an int:
> 
> 	int get_mempolicy(int *policy, unsigned long *nmask,
> 			  unsigned long maxnode, unsigned long addr,
> 			  unsigned long flags);
> 
> although the only possible values is the range of type unsigned short.
> 
> Cc: Paul Jackson <pj@....com>
> Cc: Christoph Lameter <clameter@....com>
> Cc: Lee Schermerhorn <Lee.Schermerhorn@...com>
> Cc: Andi Kleen <ak@...e.de>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  Applies on top of V3 of Lee Schermerhorn's mempolicy patch posted to
>  LKML on February 8.
> 
>  include/linux/mempolicy.h |   21 +++++++++++----------
>  include/linux/shmem_fs.h  |    2 +-
>  mm/mempolicy.c            |   29 +++++++++++++++++------------
>  mm/shmem.c                |   11 ++++++-----
>  4 files changed, 35 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -9,12 +9,13 @@
>   */
>  
>  /* Policies */
> -#define MPOL_DEFAULT	0
> -#define MPOL_PREFERRED	1
> -#define MPOL_BIND	2
> -#define MPOL_INTERLEAVE	3
> -
> -#define MPOL_MAX MPOL_INTERLEAVE
> +enum mempolicy_mode {
> +	MPOL_DEFAULT,
> +	MPOL_PREFERRED,
> +	MPOL_BIND,
> +	MPOL_INTERLEAVE,
> +	MPOL_MAX,	/* always last member of mempolicy_mode */
> +};
>  
>  /* Flags for get_mem_policy */
>  #define MPOL_F_NODE	(1<<0)	/* return next IL mode instead of node mask */
> @@ -62,7 +63,7 @@ struct mm_struct;
>   */
>  struct mempolicy {
>  	atomic_t refcnt;
> -	short policy; 	/* See MPOL_* above */
> +	unsigned short policy; 	/* See MPOL_* above */
>  	union {
>  		struct zonelist  *zonelist;	/* bind */
>  		short 		 preferred_node; /* preferred */
> @@ -133,8 +134,8 @@ struct shared_policy {
>  	spinlock_t lock;
>  };
>  
> -void mpol_shared_policy_init(struct shared_policy *info, int policy,
> -				nodemask_t *nodes);
> +void mpol_shared_policy_init(struct shared_policy *info,
> +		enum mempolicy_mode policy, nodemask_t *nodes);

Perhaps just my own myopia, but I don't see the benefit of this change;
especially when taken with the subsequent patch [2/4].  The only place
we pass around a "naked" policy member [outside of a mempolicy struct]
is between the sys call interface [and shmem_sb_info] and the
mpol_check_policy()/mpol_new() functions.  In the subsequent patch,
you'll add the optional flags to this member and this type change either
requires a separate argument [as you've done] or requires undoing this
change [as I'd like to see].

Why not leave it as an int.  Will simplify this and subsequent patch.
See comments there.

Other than that, I'm fine with this patch.

>  int mpol_set_shared_policy(struct shared_policy *info,
>  				struct vm_area_struct *vma,
>  				struct mempolicy *new);
> @@ -200,7 +201,7 @@ static inline int mpol_set_shared_policy(struct shared_policy *info,
>  }
>  
>  static inline void mpol_shared_policy_init(struct shared_policy *info,
> -					int policy, nodemask_t *nodes)
> +			enum mempolicy_type policy, nodemask_t *nodes)
>  {
>  }
>  
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -34,7 +34,7 @@ struct shmem_sb_info {
>  	uid_t uid;		    /* Mount uid for root directory */
>  	gid_t gid;		    /* Mount gid for root directory */
>  	mode_t mode;		    /* Mount mode for root directory */
> -	int policy;		    /* Default NUMA memory alloc policy */
> +	unsigned short policy;	    /* Default NUMA memory alloc policy */
>  	nodemask_t policy_nodes;    /* nodemask for preferred and bind */
>  };
>  
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -114,7 +114,7 @@ static void mpol_rebind_policy(struct mempolicy *pol,
>                                 const nodemask_t *newmask);
>  
>  /* Do sanity checking on a policy */
> -static int mpol_check_policy(int mode, nodemask_t *nodes)
> +static int mpol_check_policy(enum mempolicy_mode mode, nodemask_t *nodes)
>  {
>  	int was_empty, is_empty;
>  
> @@ -159,6 +159,8 @@ static int mpol_check_policy(int mode, nodemask_t *nodes)
>  		if (!was_empty && is_empty)
>  			return -EINVAL;
>  		break;
> +	default:
> +		BUG();
>  	}
>  	return 0;
>  }
> @@ -201,7 +203,7 @@ static struct zonelist *bind_zonelist(nodemask_t *nodes)
>  }
>  
>  /* Create a new policy */
> -static struct mempolicy *mpol_new(int mode, nodemask_t *nodes)
> +static struct mempolicy *mpol_new(enum mempolicy_mode mode, nodemask_t *nodes)
>  {
>  	struct mempolicy *policy;
>  
> @@ -235,6 +237,8 @@ static struct mempolicy *mpol_new(int mode, nodemask_t *nodes)
>  			return error_code;
>  		}
>  		break;
> +	default:
> +		BUG();
>  	}
>  	policy->policy = mode;
>  	policy->cpuset_mems_allowed = cpuset_mems_allowed(current);
> @@ -479,7 +483,7 @@ static void mpol_set_task_struct_flag(void)
>  }
>  
>  /* Set the process memory policy */
> -static long do_set_mempolicy(int mode, nodemask_t *nodes)
> +static long do_set_mempolicy(enum mempolicy_mode mode, nodemask_t *nodes)
>  {
>  	struct mempolicy *new;
>  
> @@ -781,7 +785,7 @@ static struct page *new_vma_page(struct page *page, unsigned long private, int *
>  #endif
>  
>  static long do_mbind(unsigned long start, unsigned long len,
> -		     unsigned long mode, nodemask_t *nmask,
> +		     enum mempolicy_mode mode, nodemask_t *nmask,
>  		     unsigned long flags)
>  {
>  	struct vm_area_struct *vma;
> @@ -791,9 +795,8 @@ static long do_mbind(unsigned long start, unsigned long len,
>  	int err;
>  	LIST_HEAD(pagelist);
>  
> -	if ((flags & ~(unsigned long)(MPOL_MF_STRICT |
> +	if (flags & ~(unsigned long)(MPOL_MF_STRICT |
>  				      MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
> -	    || mode > MPOL_MAX)
>  		return -EINVAL;
>  	if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
>  		return -EPERM;
> @@ -826,7 +829,7 @@ static long do_mbind(unsigned long start, unsigned long len,
>  	if (!new)
>  		flags |= MPOL_MF_DISCONTIG_OK;
>  
> -	pr_debug("mbind %lx-%lx mode:%ld nodes:%lx\n",start,start+len,
> +	pr_debug("mbind %lx-%lx mode:%d nodes:%lx\n",start,start+len,
>  		 mode, nmask ? nodes_addr(*nmask)[0] : -1);
>  
>  	down_write(&mm->mmap_sem);
> @@ -927,6 +930,8 @@ asmlinkage long sys_mbind(unsigned long start, unsigned long len,
>  	nodemask_t nodes;
>  	int err;
>  
> +	if (mode >= MPOL_MAX)
> +		return -EINVAL;
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
>  		return err;
> @@ -940,7 +945,7 @@ asmlinkage long sys_set_mempolicy(int mode, unsigned long __user *nmask,
>  	int err;
>  	nodemask_t nodes;
>  
> -	if (mode < 0 || mode > MPOL_MAX)
> +	if (mode < 0 || mode >= MPOL_MAX)
>  		return -EINVAL;
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
> @@ -1206,7 +1211,7 @@ static unsigned interleave_nodes(struct mempolicy *policy)
>   */
>  unsigned slab_node(struct mempolicy *policy)
>  {
> -	int pol = policy ? policy->policy : MPOL_DEFAULT;
> +	enum mempolicy_mode pol = policy ? policy->policy : MPOL_DEFAULT;
>  
>  	switch (pol) {
>  	case MPOL_INTERLEAVE:
> @@ -1634,8 +1639,8 @@ restart:
>  	return 0;
>  }
>  
> -void mpol_shared_policy_init(struct shared_policy *info, int policy,
> -				nodemask_t *policy_nodes)
> +void mpol_shared_policy_init(struct shared_policy *info,
> +		enum mempolicy_mode policy, nodemask_t *policy_nodes)
>  {
>  	info->root = RB_ROOT;
>  	spin_lock_init(&info->lock);
> @@ -1853,7 +1858,7 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>  	char *p = buffer;
>  	int l;
>  	nodemask_t nodes;
> -	int mode = pol ? pol->policy : MPOL_DEFAULT;
> +	enum mempolicy_mode mode = pol ? pol->policy : MPOL_DEFAULT;
>  
>  	switch (mode) {
>  	case MPOL_DEFAULT:
> diff --git a/mm/shmem.c b/mm/shmem.c
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1082,7 +1082,8 @@ redirty:
>  
>  #ifdef CONFIG_NUMA
>  #ifdef CONFIG_TMPFS
> -static int shmem_parse_mpol(char *value, int *policy, nodemask_t *policy_nodes)
> +static int shmem_parse_mpol(char *value, unsigned short *policy,
> +			    nodemask_t *policy_nodes)
>  {
>  	char *nodelist = strchr(value, ':');
>  	int err = 1;
> @@ -1131,7 +1132,7 @@ out:
>  	return err;
>  }
>  
> -static void shmem_show_mpol(struct seq_file *seq, int policy,
> +static void shmem_show_mpol(struct seq_file *seq, enum mempolicy_mode policy,
>  			    const nodemask_t policy_nodes)
>  {
>  	char *policy_string;
> @@ -1200,14 +1201,14 @@ static struct page *shmem_alloc_page(gfp_t gfp,
>  }
>  #else /* !CONFIG_NUMA */
>  #ifdef CONFIG_TMPFS
> -static inline int shmem_parse_mpol(char *value, int *policy,
> +static inline int shmem_parse_mpol(char *value, unsigned short *policy,
>  						nodemask_t *policy_nodes)
>  {
>  	return 1;
>  }
>  
> -static inline void shmem_show_mpol(struct seq_file *seq, int policy,
> -			    const nodemask_t policy_nodes)
> +static inline void shmem_show_mpol(struct seq_file *seq,
> +		enum mempolicy_mode policy, const nodemask_t policy_nodes)
>  {
>  }
>  #endif /* CONFIG_TMPFS */

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