Re: [patch 2/4] mempolicy: support optional mode flags

[Lee Schermerhorn]

On Mon, 2008-02-11 at 07:30 -0800, David Rientjes wrote: 
> With the evolution of mempolicies, it is necessary to support mempolicy
> mode flags that specify how the policy shall behave in certain
> circumstances.  The most immediate need for mode flag support is to
> suppress remapping the nodemask of a policy at the time of rebind.
> 
> With the small number of possible mempolicy modes (currently four) and
> the large size of the struct mempolicy member that stores this mode
> (unsigned short), it is possible to store both the mode and optional mode
> flags in the same member.
> 
> To do this, it is necessary to mask off the optional mode flag bits when
> testing the mempolicy mode.  A new constant, MPOL_FLAG_SHIFT, indicates
> the shift necessary to find the flag bits within struct mempolicy's
> policy member.  With this, MPOL_MODE_MASK can be defined to mask off the
> optional flags, yielding just the mode itself.
> 
> A helper function:
> 
> 	unsigned char mpol_mode(unsigned short mode)
> 
> has been implemented to return only a policy's mode.  Notice that the
> return type is unsigned char since MPOL_FLAG_SHIFT is currently defined
> at eight.  mpol_flags(unsigned short mode) does the inverse.
> 
> While this requires frequent use of mpol_mode() within the internal
> mempolicy code, it is easy to distinguish between actuals that contain
> only modes and those that contain the entire policy member (modes and
> flags).  If the formal uses enum mempolicy_mode, only the mode itself
> may successfully be passed because of type checking.

What is the benefit of pulling the flags and mode apart at the user
interface, passing them as separate args to mpol_new(), do_* and
mpol_shared_policy_init() and then stitching them back together in
mpol_new()?   Modes passed in via [sys_]{set_mempolicy|mbind}() and
those stored in the the shmem_sb_info can already have the flags there,
so this seems like extra work.

I think this patch and the previous one [1/4] would be simplified if the
formal parameters were left as an int [mabye, unsigned]  and the flags
were masked of when necessary in mpol_new() and elsewhere.

[more comments below]

> 
> Note that this does not break userspace code that relies on
> get_mempolicy(&policy, ...) and either 'switch (policy)' statements or
> 'if (policy == MPOL_INTERLEAVE)' statements.  Such applications would
> need to use optional mode flags when calling set_mempolicy() or mbind()
> for these previously implemented statements to stop working.  If an
> application does start using optional mode flags, it will need to use
> mpol_mode() in switch and conditional statements that only test mode.

> Cc: Paul Jackson <pj@xxxxxxx>
> Cc: Christoph Lameter <clameter@xxxxxxx>
> Cc: Lee Schermerhorn <Lee.Schermerhorn@xxxxxx>
> Cc: Andi Kleen <ak@xxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
>  fs/hugetlbfs/inode.c      |    2 +-
>  include/linux/mempolicy.h |   39 +++++++++++++++++++++--
>  mm/mempolicy.c            |   77 ++++++++++++++++++++++++++------------------
>  mm/shmem.c                |   15 ++++++--
>  4 files changed, 93 insertions(+), 40 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -504,7 +504,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb, uid_t uid,
>  		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
>  		INIT_LIST_HEAD(&inode->i_mapping->private_list);
>  		info = HUGETLBFS_I(inode);
> -		mpol_shared_policy_init(&info->policy, MPOL_DEFAULT, NULL);
> +		mpol_shared_policy_init(&info->policy, MPOL_DEFAULT, 0, NULL);
>  		switch (mode & S_IFMT) {
>  		default:
>  			init_special_inode(inode, mode, dev);
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -17,7 +17,18 @@ enum mempolicy_mode {
>  	MPOL_MAX,	/* always last member of mempolicy_mode */
>  };
>  
> -/* Flags for get_mem_policy */
> +/*
> + * The lower MPOL_FLAG_SHIFT bits of the policy mode represent the MPOL_*
> + * constants defined in enum mempolicy_mode.  The upper bits represent
> + * optional set_mempolicy() MPOL_F_* mode flags.
> + */
> +#define MPOL_FLAG_SHIFT	(8)
> +#define MPOL_MODE_MASK	((1 << MPOL_FLAG_SHIFT) - 1)
> +
> +/* Flags for set_mempolicy */
> +#define MPOL_MODE_FLAGS	(0)	/* legal set_mempolicy() MPOL_* mode flags */
> +
> +/* Flags for get_mempolicy */
>  #define MPOL_F_NODE	(1<<0)	/* return next IL mode instead of node mask */
>  #define MPOL_F_ADDR	(1<<1)	/* look up vma using address */
>  #define MPOL_F_MEMS_ALLOWED (1<<2) /* return allowed memories */
> @@ -115,6 +126,16 @@ static inline int mpol_equal(struct mempolicy *a, struct mempolicy *b)
>  
>  #define mpol_set_vma_default(vma) ((vma)->vm_policy = NULL)
>  
> +static inline unsigned char mpol_mode(unsigned short mode)
> +{
> +	return mode & MPOL_MODE_MASK;
> +}
> +
> +static inline unsigned short mpol_flags(unsigned short mode)
> +{
> +	return mode & ~MPOL_MODE_MASK;
> +}
> +
>  /*
>   * Tree of shared policies for a shared memory region.
>   * Maintain the policies in a pseudo mm that contains vmas. The vmas
> @@ -135,7 +156,8 @@ struct shared_policy {
>  };
>  
>  void mpol_shared_policy_init(struct shared_policy *info,
> -		enum mempolicy_mode policy, nodemask_t *nodes);
> +		enum mempolicy_mode policy, unsigned short flags,
> +		nodemask_t *nodes);
>  int mpol_set_shared_policy(struct shared_policy *info,
>  				struct vm_area_struct *vma,
>  				struct mempolicy *new);
> @@ -176,6 +198,16 @@ static inline int mpol_equal(struct mempolicy *a, struct mempolicy *b)
>  }
>  #define vma_mpol_equal(a,b) 1
>  
> +static inline unsigned char mpol_mode(unsigned short mode)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned short mpol_flags(unsigned short mode)
> +{
> +	return 0;
> +}
> +
>  #define mpol_set_vma_default(vma) do {} while(0)
>  
>  static inline void mpol_free(struct mempolicy *p)
> @@ -201,7 +233,8 @@ static inline int mpol_set_shared_policy(struct shared_policy *info,
>  }
>  
>  static inline void mpol_shared_policy_init(struct shared_policy *info,
> -			enum mempolicy_type policy, nodemask_t *nodes)
> +			enum mempolicy_type policy, unsigned short flags,
> +			nodemask_t *nodes)
>  {
>  }
>  
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -203,18 +203,20 @@ static struct zonelist *bind_zonelist(nodemask_t *nodes)
>  }
>  
>  /* Create a new policy */
> -static struct mempolicy *mpol_new(enum mempolicy_mode mode, nodemask_t *nodes)
> +static struct mempolicy *mpol_new(enum mempolicy_mode mode,
> +				  unsigned short flags, nodemask_t *nodes)
>  {
>  	struct mempolicy *policy;
>  
> -	pr_debug("setting mode %d nodes[0] %lx\n",
> -		 mode, nodes ? nodes_addr(*nodes)[0] : -1);
> +	pr_debug("setting mode %d flags %d nodes[0] %lx\n",
> +		 mode, flags, nodes ? nodes_addr(*nodes)[0] : -1);
>  
>  	if (mode == MPOL_DEFAULT)
>  		return NULL;
>  	policy = kmem_cache_alloc(policy_cache, GFP_KERNEL);
>  	if (!policy)
>  		return ERR_PTR(-ENOMEM);
> +	flags &= MPOL_MODE_FLAGS;
>  	atomic_set(&policy->refcnt, 1);
>  	switch (mode) {
>  	case MPOL_INTERLEAVE:
> @@ -240,7 +242,7 @@ static struct mempolicy *mpol_new(enum mempolicy_mode mode, nodemask_t *nodes)
>  	default:
>  		BUG();
>  	}
> -	policy->policy = mode;
> +	policy->policy = mode | flags;
>  	policy->cpuset_mems_allowed = cpuset_mems_allowed(current);
>  	return policy;
>  }
> @@ -483,19 +485,20 @@ static void mpol_set_task_struct_flag(void)
>  }
>  
>  /* Set the process memory policy */
> -static long do_set_mempolicy(enum mempolicy_mode mode, nodemask_t *nodes)
> +static long do_set_mempolicy(enum mempolicy_mode mode, unsigned short flags,
> +			     nodemask_t *nodes)
>  {
>  	struct mempolicy *new;
>  
>  	if (mpol_check_policy(mode, nodes))
>  		return -EINVAL;
> -	new = mpol_new(mode, nodes);
> +	new = mpol_new(mode, flags, nodes);
>  	if (IS_ERR(new))
>  		return PTR_ERR(new);
>  	mpol_free(current->mempolicy);
>  	current->mempolicy = new;
>  	mpol_set_task_struct_flag();
> -	if (new && new->policy == MPOL_INTERLEAVE)
> +	if (new && mpol_mode(new->policy) == MPOL_INTERLEAVE)
>  		current->il_next = first_node(new->v.nodes);
>  	return 0;
>  }
> @@ -506,7 +509,7 @@ static void get_zonemask(struct mempolicy *p, nodemask_t *nodes)
>  	int i;
>  
>  	nodes_clear(*nodes);
> -	switch (p->policy) {
> +	switch (mpol_mode(p->policy)) {
>  	case MPOL_BIND:
>  		for (i = 0; p->v.zonelist->zones[i]; i++)
>  			node_set(zone_to_nid(p->v.zonelist->zones[i]),
> @@ -588,7 +591,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
>  				goto out;
>  			*policy = err;
>  		} else if (pol == current->mempolicy &&
> -				pol->policy == MPOL_INTERLEAVE) {
> +				mpol_mode(pol->policy) == MPOL_INTERLEAVE) {
>  			*policy = current->il_next;
>  		} else {
>  			err = -EINVAL;
> @@ -785,8 +788,8 @@ static struct page *new_vma_page(struct page *page, unsigned long private, int *
>  #endif
>  
>  static long do_mbind(unsigned long start, unsigned long len,
> -		     enum mempolicy_mode mode, nodemask_t *nmask,
> -		     unsigned long flags)
> +		     enum mempolicy_mode mode, unsigned short mode_flags,
> +		     nodemask_t *nmask, unsigned long flags)
>  {
>  	struct vm_area_struct *vma;
>  	struct mm_struct *mm = current->mm;
> @@ -818,7 +821,7 @@ static long do_mbind(unsigned long start, unsigned long len,
>  	if (mpol_check_policy(mode, nmask))
>  		return -EINVAL;
>  
> -	new = mpol_new(mode, nmask);
> +	new = mpol_new(mode, mode_flags, nmask);
>  	if (IS_ERR(new))
>  		return PTR_ERR(new);
>  
> @@ -829,8 +832,9 @@ static long do_mbind(unsigned long start, unsigned long len,
>  	if (!new)
>  		flags |= MPOL_MF_DISCONTIG_OK;
>  
> -	pr_debug("mbind %lx-%lx mode:%d nodes:%lx\n",start,start+len,
> -		 mode, nmask ? nodes_addr(*nmask)[0] : -1);
> +	pr_debug("mbind %lx-%lx mode:%d flags:%d nodes:%lx\n",
> +		 start, start + len, mode, mode_flags,
> +		 nmask ? nodes_addr(*nmask)[0] : -1);
>  
>  	down_write(&mm->mmap_sem);
>  	vma = check_range(mm, start, end, nmask,
> @@ -929,13 +933,16 @@ asmlinkage long sys_mbind(unsigned long start, unsigned long len,
>  {
>  	nodemask_t nodes;
>  	int err;
> +	unsigned short mode_flags;
>  
> +	mode_flags = mpol_flags(mode);
> 
> 
I suggest restricting the flags to the defined flags here.  This gives
us the ability to defined new flags w/o breaking [changing behavior of]
applications that accidently pass undefined flags.  An error return
forced the user to fix the application [assuming they check error
returns].

> +	mode = mpol_mode(mode);
>  	if (mode >= MPOL_MAX)
>  		return -EINVAL;
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
>  		return err;
> -	return do_mbind(start, len, mode, &nodes, flags);
> +	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
>  }
>  
>  /* Set the process memory policy */
> @@ -944,13 +951,16 @@ asmlinkage long sys_set_mempolicy(int mode, unsigned long __user *nmask,
>  {
>  	int err;
>  	nodemask_t nodes;
> +	unsigned short flags;
>  
> +	flags = mpol_flags(mode);

Suggest similar arg checking here.

> +	mode = mpol_mode(mode);
>  	if (mode < 0 || mode >= MPOL_MAX)

Now that we're extracting an unsigned char from the mode via
mpol_mode(), I think we can drop the 'mode < 0 ||'.  This would also be
the case if we didn't pull the flags and mode apart and just used:

if (mpol_mode(mode) < MPOL_MAX)
...

>  		return -EINVAL;
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
>  		return err;
> -	return do_set_mempolicy(mode, &nodes);
> +	return do_set_mempolicy(mode, flags, &nodes);
>  }
>  
>  asmlinkage long sys_migrate_pages(pid_t pid, unsigned long maxnode,
> @@ -1152,7 +1162,7 @@ static struct mempolicy * get_vma_policy(struct task_struct *task,
>  			pol = vma->vm_ops->get_policy(vma, addr);
>  			shared_pol = 1;	/* if pol non-NULL, add ref below */
>  		} else if (vma->vm_policy &&
> -				vma->vm_policy->policy != MPOL_DEFAULT)
> +			   mpol_mode(vma->vm_policy->policy) != MPOL_DEFAULT)
>  			pol = vma->vm_policy;
>  	}
>  	if (!pol)
> @@ -1167,7 +1177,7 @@ static struct zonelist *zonelist_policy(gfp_t gfp, struct mempolicy *policy)
>  {
>  	int nd;
>  
> -	switch (policy->policy) {
> +	switch (mpol_mode(policy->policy)) {
>  	case MPOL_PREFERRED:
>  		nd = policy->v.preferred_node;
>  		if (nd < 0)
> @@ -1211,7 +1221,8 @@ static unsigned interleave_nodes(struct mempolicy *policy)
>   */
>  unsigned slab_node(struct mempolicy *policy)
>  {
> -	enum mempolicy_mode pol = policy ? policy->policy : MPOL_DEFAULT;
> +	enum mempolicy_mode pol = policy ? mpol_mode(policy->policy) :
> +					   MPOL_DEFAULT;
>  
>  	switch (pol) {
>  	case MPOL_INTERLEAVE:
> @@ -1297,7 +1308,7 @@ struct zonelist *huge_zonelist(struct vm_area_struct *vma, unsigned long addr,
>  	struct zonelist *zl;
>  
>  	*mpol = NULL;		/* probably no unref needed */
> -	if (pol->policy == MPOL_INTERLEAVE) {
> +	if (mpol_mode(pol->policy) == MPOL_INTERLEAVE) {
>  		unsigned nid;
>  
>  		nid = interleave_nid(pol, vma, addr, HPAGE_SHIFT);
> @@ -1307,7 +1318,7 @@ struct zonelist *huge_zonelist(struct vm_area_struct *vma, unsigned long addr,
>  
>  	zl = zonelist_policy(GFP_HIGHUSER, pol);
>  	if (unlikely(pol != &default_policy && pol != current->mempolicy)) {
> -		if (pol->policy != MPOL_BIND)
> +		if (mpol_mode(pol->policy) != MPOL_BIND)
>  			__mpol_free(pol);	/* finished with pol */
>  		else
>  			*mpol = pol;	/* unref needed after allocation */
> @@ -1361,7 +1372,7 @@ alloc_page_vma(gfp_t gfp, struct vm_area_struct *vma, unsigned long addr)
>  
>  	cpuset_update_task_memory_state();
>  
> -	if (unlikely(pol->policy == MPOL_INTERLEAVE)) {
> +	if (unlikely(mpol_mode(pol->policy) == MPOL_INTERLEAVE)) {
>  		unsigned nid;
>  
>  		nid = interleave_nid(pol, vma, addr, PAGE_SHIFT);
> @@ -1409,7 +1420,7 @@ struct page *alloc_pages_current(gfp_t gfp, unsigned order)
>  		cpuset_update_task_memory_state();
>  	if (!pol || in_interrupt() || (gfp & __GFP_THISNODE))
>  		pol = &default_policy;
> -	if (pol->policy == MPOL_INTERLEAVE)
> +	if (mpol_mode(pol->policy) == MPOL_INTERLEAVE)
>  		return alloc_page_interleave(gfp, order, interleave_nodes(pol));
>  	return __alloc_pages(gfp, order, zonelist_policy(gfp, pol));
>  }
> @@ -1436,7 +1447,7 @@ struct mempolicy *__mpol_copy(struct mempolicy *old)
>  	}
>  	*new = *old;
>  	atomic_set(&new->refcnt, 1);
> -	if (new->policy == MPOL_BIND) {
> +	if (mpol_mode(new->policy) == MPOL_BIND) {
>  		int sz = ksize(old->v.zonelist);
>  		new->v.zonelist = kmemdup(old->v.zonelist, sz, GFP_KERNEL);
>  		if (!new->v.zonelist) {
> @@ -1454,7 +1465,7 @@ int __mpol_equal(struct mempolicy *a, struct mempolicy *b)
>  		return 0;
>  	if (a->policy != b->policy)
>  		return 0;
> -	switch (a->policy) {
> +	switch (mpol_mode(a->policy)) {
>  	case MPOL_DEFAULT:
>  		return 1;
>  	case MPOL_INTERLEAVE:
> @@ -1479,7 +1490,7 @@ void __mpol_free(struct mempolicy *p)
>  {
>  	if (!atomic_dec_and_test(&p->refcnt))
>  		return;
> -	if (p->policy == MPOL_BIND)
> +	if (mpol_mode(p->policy) == MPOL_BIND)
>  		kfree(p->v.zonelist);
>  	p->policy = MPOL_DEFAULT;
>  	kmem_cache_free(policy_cache, p);
> @@ -1640,7 +1651,8 @@ restart:
>  }
>  
>  void mpol_shared_policy_init(struct shared_policy *info,
> -		enum mempolicy_mode policy, nodemask_t *policy_nodes)
> +		enum mempolicy_mode policy, unsigned short flags,
> +		nodemask_t *policy_nodes)
>  {
>  	info->root = RB_ROOT;
>  	spin_lock_init(&info->lock);
> @@ -1649,7 +1661,7 @@ void mpol_shared_policy_init(struct shared_policy *info,
>  		struct mempolicy *newpol;
>  
>  		/* Falls back to MPOL_DEFAULT on any error */
> -		newpol = mpol_new(policy, policy_nodes);
> +		newpol = mpol_new(policy, flags, policy_nodes);
>  		if (!IS_ERR(newpol)) {
>  			/* Create pseudo-vma that contains just the policy */
>  			struct vm_area_struct pvma;
> @@ -1745,14 +1757,14 @@ void __init numa_policy_init(void)
>  	if (unlikely(nodes_empty(interleave_nodes)))
>  		node_set(prefer, interleave_nodes);
>  
> -	if (do_set_mempolicy(MPOL_INTERLEAVE, &interleave_nodes))
> +	if (do_set_mempolicy(MPOL_INTERLEAVE, 0, &interleave_nodes))
>  		printk("numa_policy_init: interleaving failed\n");
>  }
>  
>  /* Reset policy of current process to default */
>  void numa_default_policy(void)
>  {
> -	do_set_mempolicy(MPOL_DEFAULT, NULL);
> +	do_set_mempolicy(MPOL_DEFAULT, 0, NULL);
>  }
>  
>  /* Migrate a policy to a different set of nodes */
> @@ -1768,7 +1780,7 @@ static void mpol_rebind_policy(struct mempolicy *pol,
>  	if (nodes_equal(*mpolmask, *newmask))
>  		return;
>  
> -	switch (pol->policy) {
> +	switch (mpol_mode(pol->policy)) {
>  	case MPOL_DEFAULT:
>  		break;
>  	case MPOL_INTERLEAVE:
> @@ -1858,7 +1870,8 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>  	char *p = buffer;
>  	int l;
>  	nodemask_t nodes;
> -	enum mempolicy_mode mode = pol ? pol->policy : MPOL_DEFAULT;
> +	enum mempolicy_mode mode = pol ? mpol_mode(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
> @@ -1086,6 +1086,7 @@ static int shmem_parse_mpol(char *value, unsigned short *policy,
>  			    nodemask_t *policy_nodes)
>  {
>  	char *nodelist = strchr(value, ':');
> +	char *flags = strchr(value, '=');
>  	int err = 1;
>  
>  	if (nodelist) {
> @@ -1096,6 +1097,8 @@ static int shmem_parse_mpol(char *value, unsigned short *policy,
>  		if (!nodes_subset(*policy_nodes, node_states[N_HIGH_MEMORY]))
>  			goto out;
>  	}
> +	if (flags)
> +		*flags++ = '\0';
>  	if (!strcmp(value, "default")) {
>  		*policy = MPOL_DEFAULT;
>  		/* Don't allow a nodelist */
> @@ -1125,6 +1128,8 @@ static int shmem_parse_mpol(char *value, unsigned short *policy,
>  			*policy_nodes = node_states[N_HIGH_MEMORY];
>  		err = 0;
>  	}
> +	if (flags) {
> +	}
>  out:
>  	/* Restore string for error message */
>  	if (nodelist)
> @@ -1154,7 +1159,7 @@ static void shmem_show_mpol(struct seq_file *seq, enum mempolicy_mode policy,
>  
>  	seq_printf(seq, ",mpol=%s", policy_string);
>  
> -	if (policy != MPOL_INTERLEAVE ||
> +	if (mpol_mode(policy) != MPOL_INTERLEAVE ||
>  	    !nodes_equal(policy_nodes, node_states[N_HIGH_MEMORY])) {
>  		char buffer[64];
>  		int len;
> @@ -1577,8 +1582,10 @@ shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
>  		case S_IFREG:
>  			inode->i_op = &shmem_inode_operations;
>  			inode->i_fop = &shmem_file_operations;
> -			mpol_shared_policy_init(&info->policy, sbinfo->policy,
> -							&sbinfo->policy_nodes);
> +			mpol_shared_policy_init(&info->policy,
> +						mpol_mode(sbinfo->policy),
> +						mpol_flags(sbinfo->policy),
> +						&sbinfo->policy_nodes);
>  			break;
>  		case S_IFDIR:
>  			inc_nlink(inode);
> @@ -1592,7 +1599,7 @@ shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
>  			 * Must not load anything in the rbtree,
>  			 * mpol_free_shared_policy will not be called.
>  			 */
> -			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT,
> +			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT, 0,
>  						NULL);
>  			break;
>  		}

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