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/mm/mempolicy.c b/mm/mempolicy.c
index 37d0b33..d77177c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -349,12 +349,6 @@
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 @@
}
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 @@
*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 @@
/* 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;
}
/*