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SubjectRe: [patch 2/4] mempolicy: support optional mode flags
On Tue, 12 Feb 2008, Lee Schermerhorn wrote:

> 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.
>

Christoph made a similiar suggestion.

> > 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].
>

That looks appropriate. It will also help in the future if certain flags
are only defined for set_mempolicy() or only defined for mbind() to either
mask them out in their respective functions or return -EINVAL.

Thanks for the comments.

David


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