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 <[email protected]>

1 files changed, 30 insertions, 4 deletions

diff --git a/module/spl/spl-vmem.c b/module/spl/spl-vmem.c
index e177988a7..dd10607dc 100644
--- a/module/spl/spl-vmem.c
+++ b/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);
-	ASSERT3S(typemask & VMEM_ALLOC, ==, VMEM_ALLOC);
-	ASSERT3S(typemask & VMEM_FREE, ==, VMEM_FREE);
+	spl_kmem_cache_t *skc;
+	size_t alloc = VMEM_FLOOR_SIZE;
+
+	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);
 
-	return (VMALLOC_TOTAL);
+	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);