Fix vmem_size()

Add a minimal implementation of vmem_size() which accounts for the
virtual memory usage of the SPL's kmem cache.  This functionality
is only useful on 32-bit systems with a small virtual address space.

The following assumptions are made:

  1) The major SPL consumer of virtual memory is the kmem cache.
  2) Memory allocated with vmem_alloc() is short lived and can be ignored.
  3) Allow a 4MB floor as a generous pad given normal consumption.
  4) The spl_kmem_cache_sem only contends with cache create/destroy.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/spl/spl-vmem.c

@@ -24,6 +24,7 @@
 
 #include <sys/debug.h>
 #include <sys/vmem.h>
+#include <sys/kmem_cache.h>
 #include <linux/mm_compat.h>
 #include <linux/module.h>
 
@@ -36,14 +37,39 @@ EXPORT_SYMBOL(zio_alloc_arena);
 vmem_t *zio_arena = NULL;
 EXPORT_SYMBOL(zio_arena);
 
+#define	VMEM_FLOOR_SIZE		(4 * 1024 * 1024)	/* 4MB floor */
+
+/*
+ * Return approximate virtual memory usage based on these assumptions:
+ *
+ * 1) The major SPL consumer of virtual memory is the kmem cache.
+ * 2) Memory allocated with vmem_alloc() is short lived and can be ignored.
+ * 3) Allow a 4MB floor as a generous pad given normal consumption.
+ * 4) The spl_kmem_cache_sem only contends with cache create/destroy.
+ */
 size_t
 vmem_size(vmem_t *vmp, int typemask)
 {
-	ASSERT3P(vmp, ==, NULL);
+	spl_kmem_cache_t *skc;
-	ASSERT3S(typemask & VMEM_ALLOC, ==, VMEM_ALLOC);
+	size_t alloc = VMEM_FLOOR_SIZE;
-	ASSERT3S(typemask & VMEM_FREE, ==, VMEM_FREE);
 
+	if ((typemask & VMEM_ALLOC) && (typemask & VMEM_FREE))
 		return (VMALLOC_TOTAL);
+
+
+	down_read(&spl_kmem_cache_sem);
+	list_for_each_entry(skc, &spl_kmem_cache_list, skc_list) {
+		if (skc->skc_flags & KMC_VMEM)
+			alloc += skc->skc_slab_size * skc->skc_slab_total;
+	}
+	up_read(&spl_kmem_cache_sem);
+
+	if (typemask & VMEM_ALLOC)
+		return (MIN(alloc, VMALLOC_TOTAL));
+	else if (typemask & VMEM_FREE)
+		return (MAX(VMALLOC_TOTAL - alloc, 0));
+	else
+		return (0);
 }
 EXPORT_SYMBOL(vmem_size);
 

module/splat/splat-kmem.c

@@ -1131,9 +1131,15 @@ out:
 static int
 splat_kmem_test10(struct file *file, void *arg)
 {
-	uint64_t size, alloc, rc = 0;
+	uint64_t size, alloc, maxsize, limit, rc = 0;
 
-	for (size = 32; size <= 1024*1024; size *= 2) {
+#if defined(CONFIG_64BIT)
+	maxsize = (1024 * 1024);
+#else
+	maxsize = (128 * 1024);
+#endif
+
+	for (size = 32; size <= maxsize; size *= 2) {
 
 		splat_vprint(file, SPLAT_KMEM_TEST10_NAME, "%-22s  %s", "name",
 			     "time (sec)\tslabs       \tobjs	\thash\n");
@@ -1142,8 +1148,10 @@ splat_kmem_test10(struct file *file, void *arg)
 
 		for (alloc = 1; alloc <= 1024; alloc *= 2) {
 
-			/* Skip tests which exceed 1/2 of physical memory. */
+			/* Skip tests which exceed 1/2 of memory. */
-			if (size * alloc * SPLAT_KMEM_THREADS > physmem / 2)
+			limit = MIN(physmem * PAGE_SIZE,
+			    vmem_size(NULL, VMEM_ALLOC | VMEM_FREE)) / 2;
+			if (size * alloc * SPLAT_KMEM_THREADS > limit)
 				continue;
 
 			rc = splat_kmem_cache_thread_test(file, arg,
@@ -1223,7 +1231,8 @@ splat_kmem_test13(struct file *file, void *arg)
 	int i, rc = 0, max_time = 10;
 
 	size = 128 * 1024;
-	count = ((physmem * PAGE_SIZE) / 4 / size);
+	count = MIN(physmem * PAGE_SIZE, vmem_size(NULL,
+	    VMEM_ALLOC | VMEM_FREE)) / 4 / size;
 
 	kcp = splat_kmem_cache_test_kcp_alloc(file, SPLAT_KMEM_TEST13_NAME,
 	                                      size, 0, 0);