[patch 03/11] mm, mempolicy: remove per-process flag

David Rientjes
2014-03-05T03:59:16Z

PF_MEMPOLICY is an unnecessary optimization for CONFIG_SLAB users.
There's no significant performance degradation to checking
current->mempolicy rather than current->flags & PF_MEMPOLICY in the
allocation path, especially since this is considered unlikely().

Running TCP_RR with netperf-2.4.5 through localhost on 16 cpu machine
with 64GB of memory and without a mempolicy:

threads before after
16 1249409 1244487
32 1281786 1246783
48 1239175 1239138
64 1244642 1241841
80 1244346 1248918
96 1266436 1254316
112 1307398 1312135
128 1327607 1326502

Per-process flags are a scarce resource so we should free them up
whenever possible and make them available. We'll be using it shortly for
memcg oom reserves.

Signed-off-by: David Rientjes <rientjes@google.com>
---
include/linux/mempolicy.h | 1 -
include/linux/sched.h | 1 -
kernel/fork.c | 1 -
mm/mempolicy.c | 31 -------------------------------
mm/slab.c | 4 ++--
5 files changed, 2 insertions(+), 36 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -143,7 +143,6 @@ extern void numa_policy_init(void);
extern void mpol_rebind_task(struct task_struct *tsk, const nodemask_t *new,
enum mpol_rebind_step step);
extern void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new);
-extern void mpol_fix_fork_child_flag(struct task_struct *p);

extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
unsigned long addr, gfp_t gfp_flags,
diff --git a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1821,7 +1821,6 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
#define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_allowed */
#define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
-#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */
#define PF_SUSPEND_TASK 0x80000000 /* this thread called freeze_processes and should not be frozen */
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1265,7 +1265,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->mempolicy = NULL;
goto bad_fork_cleanup_cgroup;
}
- mpol_fix_fork_child_flag(p);
#endif
#ifdef CONFIG_CPUSETS
p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -795,36 +795,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
return err;
}

-/*
- * Update task->flags PF_MEMPOLICY bit: set iff non-default
- * mempolicy. Allows more rapid checking of this (combined perhaps
- * with other PF_* flag bits) on memory allocation hot code paths.
- *
- * If called from outside this file, the task 'p' should -only- be
- * a newly forked child not yet visible on the task list, because
- * manipulating the task flags of a visible task is not safe.
- *
- * The above limitation is why this routine has the funny name
- * mpol_fix_fork_child_flag().
- *
- * It is also safe to call this with a task pointer of current,
- * which the static wrapper mpol_set_task_struct_flag() does,
- * for use within this file.
- */
-
-void mpol_fix_fork_child_flag(struct task_struct *p)
-{
- if (p->mempolicy)
- p->flags |= PF_MEMPOLICY;
- else
- p->flags &= ~PF_MEMPOLICY;
-}
-
-static void mpol_set_task_struct_flag(void)
-{
- mpol_fix_fork_child_flag(current);
-}
-
/* Set the process memory policy */
static long do_set_mempolicy(unsigned short mode, unsigned short flags,
nodemask_t *nodes)
@@ -861,7 +831,6 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
}
old = current->mempolicy;
current->mempolicy = new;
- mpol_set_task_struct_flag();
if (new && new->mode == MPOL_INTERLEAVE &&
nodes_weight(new->v.nodes))
current->il_next = first_node(new->v.nodes);
diff --git a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3027,7 +3027,7 @@ out:

#ifdef CONFIG_NUMA
/*
- * Try allocating on another node if PF_SPREAD_SLAB|PF_MEMPOLICY.
+ * Try allocating on another node if PF_SPREAD_SLAB is a mempolicy is set.
*
* If we are in_interrupt, then process context, including cpusets and
* mempolicy, may not apply and should not be used for allocation policy.
@@ -3259,7 +3259,7 @@ __do_cache_alloc(struct kmem_cache *cache, gfp_t flags)
{
void *objp;

- if (unlikely(current->flags & (PF_SPREAD_SLAB | PF_MEMPOLICY))) {
+ if (current->mempolicy || unlikely(current->flags & PF_SPREAD_SLAB)) {
objp = alternate_node_alloc(cache, flags);
if (objp)
goto out;