mm, mempolicy: stop adjusting current->il_next in mpol_rebind_nodemask()

The task->il_next variable stores the next allocation node id for task's
MPOL_INTERLEAVE policy.  mpol_rebind_nodemask() updates interleave and
bind mempolicies due to changing cpuset mems.  Currently it also tries
to make sure that current->il_next is valid within the updated nodemask.
This is bogus, because 1) we are updating potentially any task's
mempolicy, not just current, and 2) we might be updating a per-vma
mempolicy, not task one.

The interleave_nodes() function that uses il_next can cope fine with the
value not being within the currently allowed nodes, so this hasn't
manifested as an actual issue.

We can remove the need for updating il_next completely by changing it to
il_prev and store the node id of the previous interleave allocation
instead of the next id.  Then interleave_nodes() can calculate the next
id using the current nodemask and also store it as il_prev, except when
querying the next node via do_get_mempolicy().

Link: http://lkml.kernel.org/r/20170517081140.30654-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Christoph Lameter <cl@linux.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9c4ca7433d9d6d89aa6bad857b5299ae1bbe5577..5e8759b1b428082e4f90909107583b4caa1e5b3f 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -904,7 +904,7 @@ struct task_struct {
 #ifdef CONFIG_NUMA
        /* Protected by alloc_lock: */
        struct mempolicy                *mempolicy;
-       short                           il_next;
+       short                           il_prev;
        short                           pref_node_fork;
 #endif
 #ifdef CONFIG_NUMA_BALANCING

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 37d0b334bfe9f09222a9626a99b91f4bfca9d784..d77177c7283b397dde420c2f0680b2e290105987 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -349,12 +349,6 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes,
                pol->v.nodes = tmp;
        else
                BUG();
-
-       if (!node_isset(current->il_next, tmp)) {
-               current->il_next = next_node_in(current->il_next, tmp);
-               if (current->il_next >= MAX_NUMNODES)
-                       current->il_next = numa_node_id();
-       }
 }
 
 static void mpol_rebind_preferred(struct mempolicy *pol,
@@ -812,9 +806,8 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
        }
        old = current->mempolicy;
        current->mempolicy = new;
-       if (new && new->mode == MPOL_INTERLEAVE &&
-           nodes_weight(new->v.nodes))
-               current->il_next = first_node(new->v.nodes);
+       if (new && new->mode == MPOL_INTERLEAVE)
+               current->il_prev = MAX_NUMNODES-1;
        task_unlock(current);
        mpol_put(old);
        ret = 0;
@@ -916,7 +909,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
                        *policy = err;
                } else if (pol == current->mempolicy &&
                                pol->mode == MPOL_INTERLEAVE) {
-                       *policy = current->il_next;
+                       *policy = next_node_in(current->il_prev, pol->v.nodes);
                } else {
                        err = -EINVAL;
                        goto out;
@@ -1697,14 +1690,13 @@ static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy,
 /* Do dynamic interleaving for a process */
 static unsigned interleave_nodes(struct mempolicy *policy)
 {
-       unsigned nid, next;
+       unsigned next;
        struct task_struct *me = current;
 
-       nid = me->il_next;
-       next = next_node_in(nid, policy->v.nodes);
+       next = next_node_in(me->il_prev, policy->v.nodes);
        if (next < MAX_NUMNODES)
-               me->il_next = next;
-       return nid;
+               me->il_prev = next;
+       return next;
 }
 
 /*