Fix arc after r326347 broke various memory limit queries. Use UMA features

rather than kmem arena size to determine available memory.

Initialize the UMA limit to LONG_MAX to avoid spurious wakeups on boot before
the real limit is set.

PR:		224330 (partial), 224080
Reviewed by:	markj, avg
Sponsored by:	Netflix / Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D13494

3 files changed, 18 insertions, 6 deletions

diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index 1ea8ee06245b..1bd366416cbc 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -698,4 +698,12 @@ struct uma_percpu_stat {
 void uma_reclaim_wakeup(void);
 void uma_reclaim_worker(void *);
 
+unsigned long uma_limit(void);
+
+/* Return the amount of memory managed by UMA. */
+unsigned long uma_size(void);
+
+/* Return the amount of memory remaining.  May be negative. */
+long uma_avail(void);
+
 #endif	/* _VM_UMA_H_ */
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 81c953a48383..0dd16dd9c325 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -62,6 +62,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/eventhandler.h>
 #include <sys/kernel.h>
 #include <sys/types.h>
+#include <sys/limits.h>
 #include <sys/queue.h>
 #include <sys/malloc.h>
 #include <sys/ktr.h>
@@ -148,7 +149,7 @@ static struct mtx uma_boot_pages_mtx;
 static struct sx uma_drain_lock;
 
 /* kmem soft limit. */
-static unsigned long uma_kmem_limit;
+static unsigned long uma_kmem_limit = LONG_MAX;
 static volatile unsigned long uma_kmem_total;
 
 /* Is the VM done starting up? */
@@ -3265,7 +3266,14 @@ unsigned long
 uma_size(void)
 {
 
-	return uma_kmem_total;
+	return (uma_kmem_total);
+}
+
+long
+uma_avail(void)
+{
+
+	return (uma_kmem_limit - uma_kmem_total);
 }
 
 void
diff --git a/sys/vm/uma_int.h b/sys/vm/uma_int.h
index 158c2383c885..a8aca454f066 100644
--- a/sys/vm/uma_int.h
+++ b/sys/vm/uma_int.h
@@ -428,10 +428,6 @@ void uma_small_free(void *mem, vm_size_t size, uint8_t flags);
 
 /* Set a global soft limit on UMA managed memory. */
 void uma_set_limit(unsigned long limit);
-unsigned long uma_limit(void);
-
-/* Return the amount of memory managed by UMA. */
-unsigned long uma_size(void);
 #endif /* _KERNEL */
 
 #endif /* VM_UMA_INT_H */