Try to stabilize ZFS with regard to memory consumption:

- Allow to shrink ARC down to 16MB (instead of 64MB).
- Set arc_max to 1/2 of kmem_map by default.
- Start freeing things earlier when low memory situation is detected.
- Serialize execution of arc_lowmem().

I decided to setup minimum ZFS memory requirements to 512MB of RAM and 256MB of
kmem_map size. If there is less RAM or kmem_map, a warning will be printed.
World is cruel, be no better. In other words: modern file system requires
modern hardware:)

From ZFS administration guide:

"Currently the minimum amount of memory recommended to install a Solaris
 system is 512 Mbytes. However, for good ZFS performance, at least one
 Gbyte or more of memory is recommended."

2 files changed, 26 insertions, 8 deletions

diff --git a/sys/compat/opensolaris/kern/opensolaris_kmem.c b/sys/compat/opensolaris/kern/opensolaris_kmem.c
index 2d6f3e5..a73349f 100644
--- a/sys/compat/opensolaris/kern/opensolaris_kmem.c
+++ b/sys/compat/opensolaris/kern/opensolaris_kmem.c
@@ -31,12 +31,19 @@ __FBSDID("$FreeBSD$");
 #include <sys/kernel.h>
 #include <sys/systm.h>
 #include <sys/malloc.h>
-#include <vm/uma.h>
 #include <sys/kmem.h>
 #include <sys/debug.h>
 #include <sys/mutex.h>
+
+#include <vm/vm_page.h>
+#include <vm/vm_object.h>
+#include <vm/vm_kern.h>
+#include <vm/vm_map.h>
+
+#ifdef KMEM_DEBUG
 #include <sys/queue.h>
 #include <sys/stack.h>
+#endif
 
 #ifdef _KERNEL
 static MALLOC_DEFINE(M_SOLARIS, "solaris", "Solaris");
@@ -82,12 +89,6 @@ zfs_kmem_alloc(size_t size, int kmflags)
 	return (p);
 }
 
-void *
-kmem_zalloc(size_t size, int kmflags)
-{
-	return (kmem_alloc(size, kmflags | M_ZERO));
-}
-
 void
 zfs_kmem_free(void *buf, size_t size __unused)
 {
@@ -107,6 +108,20 @@ zfs_kmem_free(void *buf, size_t size __unused)
 	free(buf, M_SOLARIS);
 }
 
+u_long
+kmem_size(void)
+{
+
+	return ((u_long)vm_kmem_size);
+}
+
+u_long
+kmem_used(void)
+{
+
+	return ((u_long)kmem_map->size);
+}
+
 static int
 kmem_std_constructor(void *mem, int size __unused, void *private, int flags)
 {
diff --git a/sys/compat/opensolaris/sys/kmem.h b/sys/compat/opensolaris/sys/kmem.h
index 288ab7a..89dfac9 100644
--- a/sys/compat/opensolaris/sys/kmem.h
+++ b/sys/compat/opensolaris/sys/kmem.h
@@ -32,6 +32,7 @@
 #include <sys/param.h>
 #include <sys/proc.h>
 #include <sys/malloc.h>
+
 #include <vm/uma.h>
 #include <vm/vm.h>
 #include <vm/vm_extern.h>
@@ -55,8 +56,9 @@ typedef struct kmem_cache {
 } kmem_cache_t;
 
 void *zfs_kmem_alloc(size_t size, int kmflags);
-void *kmem_zalloc(size_t size, int kmflags);
 void zfs_kmem_free(void *buf, size_t size);
+u_long kmem_size(void);
+u_long kmem_used(void);
 kmem_cache_t *kmem_cache_create(char *name, size_t bufsize, size_t align,
     int (*constructor)(void *, void *, int), void (*destructor)(void *, void *),
     void (*reclaim)(void *) __unused, void *private, vmem_t *vmp, int cflags);
@@ -69,6 +71,7 @@ int kmem_debugging(void);
 void *calloc(size_t n, size_t s);
 
 #define	kmem_alloc(size, kmflags)	zfs_kmem_alloc((size), (kmflags))
+#define	kmem_zalloc(size, kmflags)	zfs_kmem_alloc((size), (kmflags) | M_ZERO)
 #define	kmem_free(buf, size)		zfs_kmem_free((buf), (size))
 
 #endif	/* _OPENSOLARIS_SYS_KMEM_H_ */