diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 1fbb5da17dd27ffa2ceb26e09614111e0955a3a9..e47761cdcb98fe4f13bdb3fd395b439ab9b5405a 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -1093,7 +1093,7 @@ static int show_spu_loadavg(struct seq_file *s, void *private)
 		LOAD_INT(c), LOAD_FRAC(c),
 		count_active_contexts(),
 		atomic_read(&nr_spu_contexts),
-		task_active_pid_ns(current)->last_pid);
+		idr_get_cursor(&task_active_pid_ns(current)->idr));
 	return 0;
 }
 
diff --git a/fs/proc/loadavg.c b/fs/proc/loadavg.c
index 9bc5c58c00ee7a97964482ccd0ad78fd73a4406c..a000d7547479e8849acbea6dea406dc5b2bb7c46 100644
--- a/fs/proc/loadavg.c
+++ b/fs/proc/loadavg.c
@@ -24,7 +24,7 @@ static int loadavg_proc_show(struct seq_file *m, void *v)
 		LOAD_INT(avnrun[1]), LOAD_FRAC(avnrun[1]),
 		LOAD_INT(avnrun[2]), LOAD_FRAC(avnrun[2]),
 		nr_running(), nr_threads,
-		task_active_pid_ns(current)->last_pid);
+		idr_get_cursor(&task_active_pid_ns(current)->idr));
 	return 0;
 }
 
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index c78af6061644f35f4dec749665a6422da2aba8ad..92c6aa509d2ea7a16f6c3fcf355ba27c64fbe5f3 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -10,15 +10,8 @@
 #include <linux/nsproxy.h>
 #include <linux/kref.h>
 #include <linux/ns_common.h>
+#include <linux/idr.h>
 
-struct pidmap {
-       atomic_t nr_free;
-       void *page;
-};
-
-#define BITS_PER_PAGE		(PAGE_SIZE * 8)
-#define BITS_PER_PAGE_MASK	(BITS_PER_PAGE-1)
-#define PIDMAP_ENTRIES		((PID_MAX_LIMIT+BITS_PER_PAGE-1)/BITS_PER_PAGE)
 
 struct fs_pin;
 
@@ -30,9 +23,8 @@ enum { /* definitions for pid_namespace's hide_pid field */
 
 struct pid_namespace {
 	struct kref kref;
-	struct pidmap pidmap[PIDMAP_ENTRIES];
+	struct idr idr;
 	struct rcu_head rcu;
-	int last_pid;
 	unsigned int nr_hashed;
 	struct task_struct *child_reaper;
 	struct kmem_cache *pid_cachep;
@@ -106,6 +98,6 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 
 extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk);
 void pidhash_init(void);
-void pidmap_init(void);
+void pid_idr_init(void);
 
 #endif /* _LINUX_PID_NS_H */
diff --git a/init/main.c b/init/main.c
index 859a786f7c0abfc32d7a7c873bc047f92585f84c..d0cbcfc06124c3040b91e3e6df5fbb9fe654eda4 100644
--- a/init/main.c
+++ b/init/main.c
@@ -669,7 +669,7 @@ asmlinkage __visible void __init start_kernel(void)
 	if (late_time_init)
 		late_time_init();
 	calibrate_delay();
-	pidmap_init();
+	pid_idr_init();
 	anon_vma_init();
 #ifdef CONFIG_X86
 	if (efi_enabled(EFI_RUNTIME_SERVICES))
diff --git a/kernel/pid.c b/kernel/pid.c
index 020dedbdf066bccbc370cba20be8dc7dbc914629..0ce59369632fec9fc7e9e7cfd2308a194f82b913 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -39,6 +39,7 @@
 #include <linux/proc_ns.h>
 #include <linux/proc_fs.h>
 #include <linux/sched/task.h>
+#include <linux/idr.h>
 
 #define pid_hashfn(nr, ns)	\
 	hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@@ -53,14 +54,6 @@ int pid_max = PID_MAX_DEFAULT;
 int pid_max_min = RESERVED_PIDS + 1;
 int pid_max_max = PID_MAX_LIMIT;
 
-static inline int mk_pid(struct pid_namespace *pid_ns,
-		struct pidmap *map, int off)
-{
-	return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
-}
-
-#define find_next_offset(map, off)					\
-		find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
 
 /*
  * PID-map pages start out as NULL, they get allocated upon
@@ -70,10 +63,7 @@ static inline int mk_pid(struct pid_namespace *pid_ns,
  */
 struct pid_namespace init_pid_ns = {
 	.kref = KREF_INIT(2),
-	.pidmap = {
-		[ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
-	},
-	.last_pid = 0,
+	.idr = IDR_INIT,
 	.nr_hashed = PIDNS_HASH_ADDING,
 	.level = 0,
 	.child_reaper = &init_task,
@@ -101,138 +91,6 @@ EXPORT_SYMBOL_GPL(init_pid_ns);
 
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
 
-static void free_pidmap(struct upid *upid)
-{
-	int nr = upid->nr;
-	struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
-	int offset = nr & BITS_PER_PAGE_MASK;
-
-	clear_bit(offset, map->page);
-	atomic_inc(&map->nr_free);
-}
-
-/*
- * If we started walking pids at 'base', is 'a' seen before 'b'?
- */
-static int pid_before(int base, int a, int b)
-{
-	/*
-	 * This is the same as saying
-	 *
-	 * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
-	 * and that mapping orders 'a' and 'b' with respect to 'base'.
-	 */
-	return (unsigned)(a - base) < (unsigned)(b - base);
-}
-
-/*
- * We might be racing with someone else trying to set pid_ns->last_pid
- * at the pid allocation time (there's also a sysctl for this, but racing
- * with this one is OK, see comment in kernel/pid_namespace.c about it).
- * We want the winner to have the "later" value, because if the
- * "earlier" value prevails, then a pid may get reused immediately.
- *
- * Since pids rollover, it is not sufficient to just pick the bigger
- * value.  We have to consider where we started counting from.
- *
- * 'base' is the value of pid_ns->last_pid that we observed when
- * we started looking for a pid.
- *
- * 'pid' is the pid that we eventually found.
- */
-static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
-{
-	int prev;
-	int last_write = base;
-	do {
-		prev = last_write;
-		last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
-	} while ((prev != last_write) && (pid_before(base, last_write, pid)));
-}
-
-static int alloc_pidmap(struct pid_namespace *pid_ns)
-{
-	int i, offset, max_scan, pid, last = pid_ns->last_pid;
-	struct pidmap *map;
-
-	pid = last + 1;
-	if (pid >= pid_max)
-		pid = RESERVED_PIDS;
-	offset = pid & BITS_PER_PAGE_MASK;
-	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
-	/*
-	 * If last_pid points into the middle of the map->page we
-	 * want to scan this bitmap block twice, the second time
-	 * we start with offset == 0 (or RESERVED_PIDS).
-	 */
-	max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
-	for (i = 0; i <= max_scan; ++i) {
-		if (unlikely(!map->page)) {
-			void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-			/*
-			 * Free the page if someone raced with us
-			 * installing it:
-			 */
-			spin_lock_irq(&pidmap_lock);
-			if (!map->page) {
-				map->page = page;
-				page = NULL;
-			}
-			spin_unlock_irq(&pidmap_lock);
-			kfree(page);
-			if (unlikely(!map->page))
-				return -ENOMEM;
-		}
-		if (likely(atomic_read(&map->nr_free))) {
-			for ( ; ; ) {
-				if (!test_and_set_bit(offset, map->page)) {
-					atomic_dec(&map->nr_free);
-					set_last_pid(pid_ns, last, pid);
-					return pid;
-				}
-				offset = find_next_offset(map, offset);
-				if (offset >= BITS_PER_PAGE)
-					break;
-				pid = mk_pid(pid_ns, map, offset);
-				if (pid >= pid_max)
-					break;
-			}
-		}
-		if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
-			++map;
-			offset = 0;
-		} else {
-			map = &pid_ns->pidmap[0];
-			offset = RESERVED_PIDS;
-			if (unlikely(last == offset))
-				break;
-		}
-		pid = mk_pid(pid_ns, map, offset);
-	}
-	return -EAGAIN;
-}
-
-int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
-{
-	int offset;
-	struct pidmap *map, *end;
-
-	if (last >= PID_MAX_LIMIT)
-		return -1;
-
-	offset = (last + 1) & BITS_PER_PAGE_MASK;
-	map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
-	end = &pid_ns->pidmap[PIDMAP_ENTRIES];
-	for (; map < end; map++, offset = 0) {
-		if (unlikely(!map->page))
-			continue;
-		offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
-		if (offset < BITS_PER_PAGE)
-			return mk_pid(pid_ns, map, offset);
-	}
-	return -1;
-}
-
 void put_pid(struct pid *pid)
 {
 	struct pid_namespace *ns;
@@ -266,7 +124,7 @@ void free_pid(struct pid *pid)
 		struct upid *upid = pid->numbers + i;
 		struct pid_namespace *ns = upid->ns;
 		hlist_del_rcu(&upid->pid_chain);
-		switch(--ns->nr_hashed) {
+		switch (--ns->nr_hashed) {
 		case 2:
 		case 1:
 			/* When all that is left in the pid namespace
@@ -284,12 +142,11 @@ void free_pid(struct pid *pid)
 			schedule_work(&ns->proc_work);
 			break;
 		}
+
+		idr_remove(&ns->idr, upid->nr);
 	}
 	spin_unlock_irqrestore(&pidmap_lock, flags);
 
-	for (i = 0; i <= pid->level; i++)
-		free_pidmap(pid->numbers + i);
-
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
@@ -308,8 +165,29 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 
 	tmp = ns;
 	pid->level = ns->level;
+
 	for (i = ns->level; i >= 0; i--) {
-		nr = alloc_pidmap(tmp);
+		int pid_min = 1;
+
+		idr_preload(GFP_KERNEL);
+		spin_lock_irq(&pidmap_lock);
+
+		/*
+		 * init really needs pid 1, but after reaching the maximum
+		 * wrap back to RESERVED_PIDS
+		 */
+		if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
+			pid_min = RESERVED_PIDS;
+
+		/*
+		 * Store a null pointer so find_pid_ns does not find
+		 * a partially initialized PID (see below).
+		 */
+		nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
+				      pid_max, GFP_ATOMIC);
+		spin_unlock_irq(&pidmap_lock);
+		idr_preload_end();
+
 		if (nr < 0) {
 			retval = nr;
 			goto out_free;
@@ -339,6 +217,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 	for ( ; upid >= pid->numbers; --upid) {
 		hlist_add_head_rcu(&upid->pid_chain,
 				&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
+		/* Make the PID visible to find_pid_ns. */
+		idr_replace(&upid->ns->idr, pid, upid->nr);
 		upid->ns->nr_hashed++;
 	}
 	spin_unlock_irq(&pidmap_lock);
@@ -350,8 +230,11 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 	put_pid_ns(ns);
 
 out_free:
+	spin_lock_irq(&pidmap_lock);
 	while (++i <= ns->level)
-		free_pidmap(pid->numbers + i);
+		idr_remove(&ns->idr, (pid->numbers + i)->nr);
+
+	spin_unlock_irq(&pidmap_lock);
 
 	kmem_cache_free(ns->pid_cachep, pid);
 	return ERR_PTR(retval);
@@ -553,16 +436,7 @@ EXPORT_SYMBOL_GPL(task_active_pid_ns);
  */
 struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 {
-	struct pid *pid;
-
-	do {
-		pid = find_pid_ns(nr, ns);
-		if (pid)
-			break;
-		nr = next_pidmap(ns, nr);
-	} while (nr > 0);
-
-	return pid;
+	return idr_get_next(&ns->idr, &nr);
 }
 
 /*
@@ -578,7 +452,7 @@ void __init pidhash_init(void)
 					   0, 4096);
 }
 
-void __init pidmap_init(void)
+void __init pid_idr_init(void)
 {
 	/* Verify no one has done anything silly: */
 	BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
@@ -590,10 +464,7 @@ void __init pidmap_init(void)
 				PIDS_PER_CPU_MIN * num_possible_cpus());
 	pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
 
-	init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	/* Reserve PID 0. We never call free_pidmap(0) */
-	set_bit(0, init_pid_ns.pidmap[0].page);
-	atomic_dec(&init_pid_ns.pidmap[0].nr_free);
+	idr_init(&init_pid_ns.idr);
 
 	init_pid_ns.pid_cachep = KMEM_CACHE(pid,
 			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 4918314893bc6620ae95660c78588d6d5ac9129c..ca7c8a8823b1fea26d4bb2074c85301b98336630 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -21,6 +21,7 @@
 #include <linux/export.h>
 #include <linux/sched/task.h>
 #include <linux/sched/signal.h>
+#include <linux/idr.h>
 
 struct pid_cache {
 	int nr_ids;
@@ -98,7 +99,6 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	struct pid_namespace *ns;
 	unsigned int level = parent_pid_ns->level + 1;
 	struct ucounts *ucounts;
-	int i;
 	int err;
 
 	err = -EINVAL;
@@ -117,17 +117,15 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	if (ns == NULL)
 		goto out_dec;
 
-	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!ns->pidmap[0].page)
-		goto out_free;
+	idr_init(&ns->idr);
 
 	ns->pid_cachep = create_pid_cachep(level + 1);
 	if (ns->pid_cachep == NULL)
-		goto out_free_map;
+		goto out_free_idr;
 
 	err = ns_alloc_inum(&ns->ns);
 	if (err)
-		goto out_free_map;
+		goto out_free_idr;
 	ns->ns.ops = &pidns_operations;
 
 	kref_init(&ns->kref);
@@ -138,17 +136,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	ns->nr_hashed = PIDNS_HASH_ADDING;
 	INIT_WORK(&ns->proc_work, proc_cleanup_work);
 
-	set_bit(0, ns->pidmap[0].page);
-	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
-
-	for (i = 1; i < PIDMAP_ENTRIES; i++)
-		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
-
 	return ns;
 
-out_free_map:
-	kfree(ns->pidmap[0].page);
-out_free:
+out_free_idr:
+	idr_destroy(&ns->idr);
 	kmem_cache_free(pid_ns_cachep, ns);
 out_dec:
 	dec_pid_namespaces(ucounts);
@@ -168,11 +159,9 @@ static void delayed_free_pidns(struct rcu_head *p)
 
 static void destroy_pid_namespace(struct pid_namespace *ns)
 {
-	int i;
-
 	ns_free_inum(&ns->ns);
-	for (i = 0; i < PIDMAP_ENTRIES; i++)
-		kfree(ns->pidmap[i].page);
+
+	idr_destroy(&ns->idr);
 	call_rcu(&ns->rcu, delayed_free_pidns);
 }
 
@@ -213,6 +202,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	int rc;
 	struct task_struct *task, *me = current;
 	int init_pids = thread_group_leader(me) ? 1 : 2;
+	struct pid *pid;
 
 	/* Don't allow any more processes into the pid namespace */
 	disable_pid_allocation(pid_ns);
@@ -239,20 +229,16 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	 * 	  maintain a tasklist for each pid namespace.
 	 *
 	 */
+	rcu_read_lock();
 	read_lock(&tasklist_lock);
-	nr = next_pidmap(pid_ns, 1);
-	while (nr > 0) {
-		rcu_read_lock();
-
-		task = pid_task(find_vpid(nr), PIDTYPE_PID);
+	nr = 2;
+	idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
+		task = pid_task(pid, PIDTYPE_PID);
 		if (task && !__fatal_signal_pending(task))
 			send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
-
-		rcu_read_unlock();
-
-		nr = next_pidmap(pid_ns, nr);
 	}
 	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 
 	/*
 	 * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
@@ -301,6 +287,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 {
 	struct pid_namespace *pid_ns = task_active_pid_ns(current);
 	struct ctl_table tmp = *table;
+	int ret, next;
 
 	if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
@@ -311,8 +298,14 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 	 * it should synchronize its usage with external means.
 	 */
 
-	tmp.data = &pid_ns->last_pid;
-	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+	next = idr_get_cursor(&pid_ns->idr) - 1;
+
+	tmp.data = &next;
+	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+	if (!ret && write)
+		idr_set_cursor(&pid_ns->idr, next + 1);
+
+	return ret;
 }
 
 extern int pid_max;