Merge branch 'zfsonlinux/merge-spl'

Merge a minimal version of the zfsonlinux/spl repository in to the
zfsonlinux/zfs repository.  Care was taken to prevent file conflicts
when merging and to preserve the spl repository history.  The spl
kernel module remains under the GPLv2 license as documented by the
additional THIRDPARTYLICENSE.gplv2 file.

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 1769 insertions, 0 deletions

diff --git a/module/spl/spl-kmem-cache.c b/module/spl/spl-kmem-cache.c
new file mode 100644
index 000000000..5492c6a46
--- /dev/null
+++ b/module/spl/spl-kmem-cache.c
@@ -0,0 +1,1769 @@
+/*
+ *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
+ *  Copyright (C) 2007 The Regents of the University of California.
+ *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
+ *  Written by Brian Behlendorf <[email protected]>.
+ *  UCRL-CODE-235197
+ *
+ *  This file is part of the SPL, Solaris Porting Layer.
+ *  For details, see <http://zfsonlinux.org/>.
+ *
+ *  The SPL is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the
+ *  Free Software Foundation; either version 2 of the License, or (at your
+ *  option) any later version.
+ *
+ *  The SPL is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ *  for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <sys/kmem.h>
+#include <sys/kmem_cache.h>
+#include <sys/shrinker.h>
+#include <sys/taskq.h>
+#include <sys/timer.h>
+#include <sys/vmem.h>
+#include <sys/wait.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/prefetch.h>
+
+/*
+ * Within the scope of spl-kmem.c file the kmem_cache_* definitions
+ * are removed to allow access to the real Linux slab allocator.
+ */
+#undef kmem_cache_destroy
+#undef kmem_cache_create
+#undef kmem_cache_alloc
+#undef kmem_cache_free
+
+
+/*
+ * Linux 3.16 replaced smp_mb__{before,after}_{atomic,clear}_{dec,inc,bit}()
+ * with smp_mb__{before,after}_atomic() because they were redundant. This is
+ * only used inside our SLAB allocator, so we implement an internal wrapper
+ * here to give us smp_mb__{before,after}_atomic() on older kernels.
+ */
+#ifndef smp_mb__before_atomic
+#define	smp_mb__before_atomic(x) smp_mb__before_clear_bit(x)
+#endif
+
+#ifndef smp_mb__after_atomic
+#define	smp_mb__after_atomic(x) smp_mb__after_clear_bit(x)
+#endif
+
+/*
+ * Cache expiration was implemented because it was part of the default Solaris
+ * kmem_cache behavior.  The idea is that per-cpu objects which haven't been
+ * accessed in several seconds should be returned to the cache.  On the other
+ * hand Linux slabs never move objects back to the slabs unless there is
+ * memory pressure on the system.  By default the Linux method is enabled
+ * because it has been shown to improve responsiveness on low memory systems.
+ * This policy may be changed by setting KMC_EXPIRE_AGE or KMC_EXPIRE_MEM.
+ */
+/* BEGIN CSTYLED */
+unsigned int spl_kmem_cache_expire = KMC_EXPIRE_MEM;
+EXPORT_SYMBOL(spl_kmem_cache_expire);
+module_param(spl_kmem_cache_expire, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_expire, "By age (0x1) or low memory (0x2)");
+
+/*
+ * Cache magazines are an optimization designed to minimize the cost of
+ * allocating memory.  They do this by keeping a per-cpu cache of recently
+ * freed objects, which can then be reallocated without taking a lock. This
+ * can improve performance on highly contended caches.  However, because
+ * objects in magazines will prevent otherwise empty slabs from being
+ * immediately released this may not be ideal for low memory machines.
+ *
+ * For this reason spl_kmem_cache_magazine_size can be used to set a maximum
+ * magazine size.  When this value is set to 0 the magazine size will be
+ * automatically determined based on the object size.  Otherwise magazines
+ * will be limited to 2-256 objects per magazine (i.e per cpu).  Magazines
+ * may never be entirely disabled in this implementation.
+ */
+unsigned int spl_kmem_cache_magazine_size = 0;
+module_param(spl_kmem_cache_magazine_size, uint, 0444);
+MODULE_PARM_DESC(spl_kmem_cache_magazine_size,
+	"Default magazine size (2-256), set automatically (0)");
+
+/*
+ * The default behavior is to report the number of objects remaining in the
+ * cache.  This allows the Linux VM to repeatedly reclaim objects from the
+ * cache when memory is low satisfy other memory allocations.  Alternately,
+ * setting this value to KMC_RECLAIM_ONCE limits how aggressively the cache
+ * is reclaimed.  This may increase the likelihood of out of memory events.
+ */
+unsigned int spl_kmem_cache_reclaim = 0 /* KMC_RECLAIM_ONCE */;
+module_param(spl_kmem_cache_reclaim, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_reclaim, "Single reclaim pass (0x1)");
+
+unsigned int spl_kmem_cache_obj_per_slab = SPL_KMEM_CACHE_OBJ_PER_SLAB;
+module_param(spl_kmem_cache_obj_per_slab, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_obj_per_slab, "Number of objects per slab");
+
+unsigned int spl_kmem_cache_obj_per_slab_min = SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN;
+module_param(spl_kmem_cache_obj_per_slab_min, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_obj_per_slab_min,
+	"Minimal number of objects per slab");
+
+unsigned int spl_kmem_cache_max_size = SPL_KMEM_CACHE_MAX_SIZE;
+module_param(spl_kmem_cache_max_size, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_max_size, "Maximum size of slab in MB");
+
+/*
+ * For small objects the Linux slab allocator should be used to make the most
+ * efficient use of the memory.  However, large objects are not supported by
+ * the Linux slab and therefore the SPL implementation is preferred.  A cutoff
+ * of 16K was determined to be optimal for architectures using 4K pages.
+ */
+#if PAGE_SIZE == 4096
+unsigned int spl_kmem_cache_slab_limit = 16384;
+#else
+unsigned int spl_kmem_cache_slab_limit = 0;
+#endif
+module_param(spl_kmem_cache_slab_limit, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_slab_limit,
+	"Objects less than N bytes use the Linux slab");
+
+/*
+ * This value defaults to a threshold designed to avoid allocations which
+ * have been deemed costly by the kernel.
+ */
+unsigned int spl_kmem_cache_kmem_limit =
+	((1 << (PAGE_ALLOC_COSTLY_ORDER - 1)) * PAGE_SIZE) /
+	SPL_KMEM_CACHE_OBJ_PER_SLAB;
+module_param(spl_kmem_cache_kmem_limit, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_kmem_limit,
+	"Objects less than N bytes use the kmalloc");
+
+/*
+ * The number of threads available to allocate new slabs for caches.  This
+ * should not need to be tuned but it is available for performance analysis.
+ */
+unsigned int spl_kmem_cache_kmem_threads = 4;
+module_param(spl_kmem_cache_kmem_threads, uint, 0444);
+MODULE_PARM_DESC(spl_kmem_cache_kmem_threads,
+	"Number of spl_kmem_cache threads");
+/* END CSTYLED */
+
+/*
+ * Slab allocation interfaces
+ *
+ * While the Linux slab implementation was inspired by the Solaris
+ * implementation I cannot use it to emulate the Solaris APIs.  I
+ * require two features which are not provided by the Linux slab.
+ *
+ * 1) Constructors AND destructors.  Recent versions of the Linux
+ *    kernel have removed support for destructors.  This is a deal
+ *    breaker for the SPL which contains particularly expensive
+ *    initializers for mutex's, condition variables, etc.  We also
+ *    require a minimal level of cleanup for these data types unlike
+ *    many Linux data types which do need to be explicitly destroyed.
+ *
+ * 2) Virtual address space backed slab.  Callers of the Solaris slab
+ *    expect it to work well for both small are very large allocations.
+ *    Because of memory fragmentation the Linux slab which is backed
+ *    by kmalloc'ed memory performs very badly when confronted with
+ *    large numbers of large allocations.  Basing the slab on the
+ *    virtual address space removes the need for contiguous pages
+ *    and greatly improve performance for large allocations.
+ *
+ * For these reasons, the SPL has its own slab implementation with
+ * the needed features.  It is not as highly optimized as either the
+ * Solaris or Linux slabs, but it should get me most of what is
+ * needed until it can be optimized or obsoleted by another approach.
+ *
+ * One serious concern I do have about this method is the relatively
+ * small virtual address space on 32bit arches.  This will seriously
+ * constrain the size of the slab caches and their performance.
+ */
+
+struct list_head spl_kmem_cache_list;   /* List of caches */
+struct rw_semaphore spl_kmem_cache_sem; /* Cache list lock */
+taskq_t *spl_kmem_cache_taskq;		/* Task queue for ageing / reclaim */
+
+static void spl_cache_shrink(spl_kmem_cache_t *skc, void *obj);
+
+SPL_SHRINKER_CALLBACK_FWD_DECLARE(spl_kmem_cache_generic_shrinker);
+SPL_SHRINKER_DECLARE(spl_kmem_cache_shrinker,
+	spl_kmem_cache_generic_shrinker, KMC_DEFAULT_SEEKS);
+
+static void *
+kv_alloc(spl_kmem_cache_t *skc, int size, int flags)
+{
+	gfp_t lflags = kmem_flags_convert(flags);
+	void *ptr;
+
+	if (skc->skc_flags & KMC_KMEM) {
+		ASSERT(ISP2(size));
+		ptr = (void *)__get_free_pages(lflags, get_order(size));
+	} else {
+		ptr = __vmalloc(size, lflags | __GFP_HIGHMEM, PAGE_KERNEL);
+	}
+
+	/* Resulting allocated memory will be page aligned */
+	ASSERT(IS_P2ALIGNED(ptr, PAGE_SIZE));
+
+	return (ptr);
+}
+
+static void
+kv_free(spl_kmem_cache_t *skc, void *ptr, int size)
+{
+	ASSERT(IS_P2ALIGNED(ptr, PAGE_SIZE));
+
+	/*
+	 * The Linux direct reclaim path uses this out of band value to
+	 * determine if forward progress is being made.  Normally this is
+	 * incremented by kmem_freepages() which is part of the various
+	 * Linux slab implementations.  However, since we are using none
+	 * of that infrastructure we are responsible for incrementing it.
+	 */
+	if (current->reclaim_state)
+		current->reclaim_state->reclaimed_slab += size >> PAGE_SHIFT;
+
+	if (skc->skc_flags & KMC_KMEM) {
+		ASSERT(ISP2(size));
+		free_pages((unsigned long)ptr, get_order(size));
+	} else {
+		vfree(ptr);
+	}
+}
+
+/*
+ * Required space for each aligned sks.
+ */
+static inline uint32_t
+spl_sks_size(spl_kmem_cache_t *skc)
+{
+	return (P2ROUNDUP_TYPED(sizeof (spl_kmem_slab_t),
+	    skc->skc_obj_align, uint32_t));
+}
+
+/*
+ * Required space for each aligned object.
+ */
+static inline uint32_t
+spl_obj_size(spl_kmem_cache_t *skc)
+{
+	uint32_t align = skc->skc_obj_align;
+
+	return (P2ROUNDUP_TYPED(skc->skc_obj_size, align, uint32_t) +
+	    P2ROUNDUP_TYPED(sizeof (spl_kmem_obj_t), align, uint32_t));
+}
+
+/*
+ * Lookup the spl_kmem_object_t for an object given that object.
+ */
+static inline spl_kmem_obj_t *
+spl_sko_from_obj(spl_kmem_cache_t *skc, void *obj)
+{
+	return (obj + P2ROUNDUP_TYPED(skc->skc_obj_size,
+	    skc->skc_obj_align, uint32_t));
+}
+
+/*
+ * Required space for each offslab object taking in to account alignment
+ * restrictions and the power-of-two requirement of kv_alloc().
+ */
+static inline uint32_t
+spl_offslab_size(spl_kmem_cache_t *skc)
+{
+	return (1UL << (fls64(spl_obj_size(skc)) + 1));
+}
+
+/*
+ * It's important that we pack the spl_kmem_obj_t structure and the
+ * actual objects in to one large address space to minimize the number
+ * of calls to the allocator.  It is far better to do a few large
+ * allocations and then subdivide it ourselves.  Now which allocator
+ * we use requires balancing a few trade offs.
+ *
+ * For small objects we use kmem_alloc() because as long as you are
+ * only requesting a small number of pages (ideally just one) its cheap.
+ * However, when you start requesting multiple pages with kmem_alloc()
+ * it gets increasingly expensive since it requires contiguous pages.
+ * For this reason we shift to vmem_alloc() for slabs of large objects
+ * which removes the need for contiguous pages.  We do not use
+ * vmem_alloc() in all cases because there is significant locking
+ * overhead in __get_vm_area_node().  This function takes a single
+ * global lock when acquiring an available virtual address range which
+ * serializes all vmem_alloc()'s for all slab caches.  Using slightly
+ * different allocation functions for small and large objects should
+ * give us the best of both worlds.
+ *
+ * KMC_ONSLAB                       KMC_OFFSLAB
+ *
+ * +------------------------+       +-----------------+
+ * | spl_kmem_slab_t --+-+  |       | spl_kmem_slab_t |---+-+
+ * | skc_obj_size    <-+ |  |       +-----------------+   | |
+ * | spl_kmem_obj_t      |  |                             | |
+ * | skc_obj_size    <---+  |       +-----------------+   | |
+ * | spl_kmem_obj_t      |  |       | skc_obj_size    | <-+ |
+ * | ...                 v  |       | spl_kmem_obj_t  |     |
+ * +------------------------+       +-----------------+     v
+ */
+static spl_kmem_slab_t *
+spl_slab_alloc(spl_kmem_cache_t *skc, int flags)
+{
+	spl_kmem_slab_t *sks;
+	spl_kmem_obj_t *sko, *n;
+	void *base, *obj;
+	uint32_t obj_size, offslab_size = 0;
+	int i,  rc = 0;
+
+	base = kv_alloc(skc, skc->skc_slab_size, flags);
+	if (base == NULL)
+		return (NULL);
+
+	sks = (spl_kmem_slab_t *)base;
+	sks->sks_magic = SKS_MAGIC;
+	sks->sks_objs = skc->skc_slab_objs;
+	sks->sks_age = jiffies;
+	sks->sks_cache = skc;
+	INIT_LIST_HEAD(&sks->sks_list);
+	INIT_LIST_HEAD(&sks->sks_free_list);
+	sks->sks_ref = 0;
+	obj_size = spl_obj_size(skc);
+
+	if (skc->skc_flags & KMC_OFFSLAB)
+		offslab_size = spl_offslab_size(skc);
+
+	for (i = 0; i < sks->sks_objs; i++) {
+		if (skc->skc_flags & KMC_OFFSLAB) {
+			obj = kv_alloc(skc, offslab_size, flags);
+			if (!obj) {
+				rc = -ENOMEM;
+				goto out;
+			}
+		} else {
+			obj = base + spl_sks_size(skc) + (i * obj_size);
+		}
+
+		ASSERT(IS_P2ALIGNED(obj, skc->skc_obj_align));
+		sko = spl_sko_from_obj(skc, obj);
+		sko->sko_addr = obj;
+		sko->sko_magic = SKO_MAGIC;
+		sko->sko_slab = sks;
+		INIT_LIST_HEAD(&sko->sko_list);
+		list_add_tail(&sko->sko_list, &sks->sks_free_list);
+	}
+
+out:
+	if (rc) {
+		if (skc->skc_flags & KMC_OFFSLAB)
+			list_for_each_entry_safe(sko,
+			    n, &sks->sks_free_list, sko_list) {
+				kv_free(skc, sko->sko_addr, offslab_size);
+			}
+
+		kv_free(skc, base, skc->skc_slab_size);
+		sks = NULL;
+	}
+
+	return (sks);
+}
+
+/*
+ * Remove a slab from complete or partial list, it must be called with
+ * the 'skc->skc_lock' held but the actual free must be performed
+ * outside the lock to prevent deadlocking on vmem addresses.
+ */
+static void
+spl_slab_free(spl_kmem_slab_t *sks,
+    struct list_head *sks_list, struct list_head *sko_list)
+{
+	spl_kmem_cache_t *skc;
+
+	ASSERT(sks->sks_magic == SKS_MAGIC);
+	ASSERT(sks->sks_ref == 0);
+
+	skc = sks->sks_cache;
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+
+	/*
+	 * Update slab/objects counters in the cache, then remove the
+	 * slab from the skc->skc_partial_list.  Finally add the slab
+	 * and all its objects in to the private work lists where the
+	 * destructors will be called and the memory freed to the system.
+	 */
+	skc->skc_obj_total -= sks->sks_objs;
+	skc->skc_slab_total--;
+	list_del(&sks->sks_list);
+	list_add(&sks->sks_list, sks_list);
+	list_splice_init(&sks->sks_free_list, sko_list);
+}
+
+/*
+ * Reclaim empty slabs at the end of the partial list.
+ */
+static void
+spl_slab_reclaim(spl_kmem_cache_t *skc)
+{
+	spl_kmem_slab_t *sks, *m;
+	spl_kmem_obj_t *sko, *n;
+	LIST_HEAD(sks_list);
+	LIST_HEAD(sko_list);
+	uint32_t size = 0;
+
+	/*
+	 * Empty slabs and objects must be moved to a private list so they
+	 * can be safely freed outside the spin lock.  All empty slabs are
+	 * at the end of skc->skc_partial_list, therefore once a non-empty
+	 * slab is found we can stop scanning.
+	 */
+	spin_lock(&skc->skc_lock);
+	list_for_each_entry_safe_reverse(sks, m,
+	    &skc->skc_partial_list, sks_list) {
+
+		if (sks->sks_ref > 0)
+			break;
+
+		spl_slab_free(sks, &sks_list, &sko_list);
+	}
+	spin_unlock(&skc->skc_lock);
+
+	/*
+	 * The following two loops ensure all the object destructors are
+	 * run, any offslab objects are freed, and the slabs themselves
+	 * are freed.  This is all done outside the skc->skc_lock since
+	 * this allows the destructor to sleep, and allows us to perform
+	 * a conditional reschedule when a freeing a large number of
+	 * objects and slabs back to the system.
+	 */
+	if (skc->skc_flags & KMC_OFFSLAB)
+		size = spl_offslab_size(skc);
+
+	list_for_each_entry_safe(sko, n, &sko_list, sko_list) {
+		ASSERT(sko->sko_magic == SKO_MAGIC);
+
+		if (skc->skc_flags & KMC_OFFSLAB)
+			kv_free(skc, sko->sko_addr, size);
+	}
+
+	list_for_each_entry_safe(sks, m, &sks_list, sks_list) {
+		ASSERT(sks->sks_magic == SKS_MAGIC);
+		kv_free(skc, sks, skc->skc_slab_size);
+	}
+}
+
+static spl_kmem_emergency_t *
+spl_emergency_search(struct rb_root *root, void *obj)
+{
+	struct rb_node *node = root->rb_node;
+	spl_kmem_emergency_t *ske;
+	unsigned long address = (unsigned long)obj;
+
+	while (node) {
+		ske = container_of(node, spl_kmem_emergency_t, ske_node);
+
+		if (address < ske->ske_obj)
+			node = node->rb_left;
+		else if (address > ske->ske_obj)
+			node = node->rb_right;
+		else
+			return (ske);
+	}
+
+	return (NULL);
+}
+
+static int
+spl_emergency_insert(struct rb_root *root, spl_kmem_emergency_t *ske)
+{
+	struct rb_node **new = &(root->rb_node), *parent = NULL;
+	spl_kmem_emergency_t *ske_tmp;
+	unsigned long address = ske->ske_obj;
+
+	while (*new) {
+		ske_tmp = container_of(*new, spl_kmem_emergency_t, ske_node);
+
+		parent = *new;
+		if (address < ske_tmp->ske_obj)
+			new = &((*new)->rb_left);
+		else if (address > ske_tmp->ske_obj)
+			new = &((*new)->rb_right);
+		else
+			return (0);
+	}
+
+	rb_link_node(&ske->ske_node, parent, new);
+	rb_insert_color(&ske->ske_node, root);
+
+	return (1);
+}
+
+/*
+ * Allocate a single emergency object and track it in a red black tree.
+ */
+static int
+spl_emergency_alloc(spl_kmem_cache_t *skc, int flags, void **obj)
+{
+	gfp_t lflags = kmem_flags_convert(flags);
+	spl_kmem_emergency_t *ske;
+	int order = get_order(skc->skc_obj_size);
+	int empty;
+
+	/* Last chance use a partial slab if one now exists */
+	spin_lock(&skc->skc_lock);
+	empty = list_empty(&skc->skc_partial_list);
+	spin_unlock(&skc->skc_lock);
+	if (!empty)
+		return (-EEXIST);
+
+	ske = kmalloc(sizeof (*ske), lflags);
+	if (ske == NULL)
+		return (-ENOMEM);
+
+	ske->ske_obj = __get_free_pages(lflags, order);
+	if (ske->ske_obj == 0) {
+		kfree(ske);
+		return (-ENOMEM);
+	}
+
+	spin_lock(&skc->skc_lock);
+	empty = spl_emergency_insert(&skc->skc_emergency_tree, ske);
+	if (likely(empty)) {
+		skc->skc_obj_total++;
+		skc->skc_obj_emergency++;
+		if (skc->skc_obj_emergency > skc->skc_obj_emergency_max)
+			skc->skc_obj_emergency_max = skc->skc_obj_emergency;
+	}
+	spin_unlock(&skc->skc_lock);
+
+	if (unlikely(!empty)) {
+		free_pages(ske->ske_obj, order);
+		kfree(ske);
+		return (-EINVAL);
+	}
+
+	*obj = (void *)ske->ske_obj;
+
+	return (0);
+}
+
+/*
+ * Locate the passed object in the red black tree and free it.
+ */
+static int
+spl_emergency_free(spl_kmem_cache_t *skc, void *obj)
+{
+	spl_kmem_emergency_t *ske;
+	int order = get_order(skc->skc_obj_size);
+
+	spin_lock(&skc->skc_lock);
+	ske = spl_emergency_search(&skc->skc_emergency_tree, obj);
+	if (ske) {
+		rb_erase(&ske->ske_node, &skc->skc_emergency_tree);
+		skc->skc_obj_emergency--;
+		skc->skc_obj_total--;
+	}
+	spin_unlock(&skc->skc_lock);
+
+	if (ske == NULL)
+		return (-ENOENT);
+
+	free_pages(ske->ske_obj, order);
+	kfree(ske);
+
+	return (0);
+}
+
+/*
+ * Release objects from the per-cpu magazine back to their slab.  The flush
+ * argument contains the max number of entries to remove from the magazine.
+ */
+static void
+__spl_cache_flush(spl_kmem_cache_t *skc, spl_kmem_magazine_t *skm, int flush)
+{
+	int i, count = MIN(flush, skm->skm_avail);
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+
+	for (i = 0; i < count; i++)
+		spl_cache_shrink(skc, skm->skm_objs[i]);
+
+	skm->skm_avail -= count;
+	memmove(skm->skm_objs, &(skm->skm_objs[count]),
+	    sizeof (void *) * skm->skm_avail);
+}
+
+static void
+spl_cache_flush(spl_kmem_cache_t *skc, spl_kmem_magazine_t *skm, int flush)
+{
+	spin_lock(&skc->skc_lock);
+	__spl_cache_flush(skc, skm, flush);
+	spin_unlock(&skc->skc_lock);
+}
+
+static void
+spl_magazine_age(void *data)
+{
+	spl_kmem_cache_t *skc = (spl_kmem_cache_t *)data;
+	spl_kmem_magazine_t *skm = skc->skc_mag[smp_processor_id()];
+
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+	ASSERT(skm->skm_cpu == smp_processor_id());
+	ASSERT(irqs_disabled());
+
+	/* There are no available objects or they are too young to age out */
+	if ((skm->skm_avail == 0) ||
+	    time_before(jiffies, skm->skm_age + skc->skc_delay * HZ))
+		return;
+
+	/*
+	 * Because we're executing in interrupt context we may have
+	 * interrupted the holder of this lock.  To avoid a potential
+	 * deadlock return if the lock is contended.
+	 */
+	if (!spin_trylock(&skc->skc_lock))
+		return;
+
+	__spl_cache_flush(skc, skm, skm->skm_refill);
+	spin_unlock(&skc->skc_lock);
+}
+
+/*
+ * Called regularly to keep a downward pressure on the cache.
+ *
+ * Objects older than skc->skc_delay seconds in the per-cpu magazines will
+ * be returned to the caches.  This is done to prevent idle magazines from
+ * holding memory which could be better used elsewhere.  The delay is
+ * present to prevent thrashing the magazine.
+ *
+ * The newly released objects may result in empty partial slabs.  Those
+ * slabs should be released to the system.  Otherwise moving the objects
+ * out of the magazines is just wasted work.
+ */
+static void
+spl_cache_age(void *data)
+{
+	spl_kmem_cache_t *skc = (spl_kmem_cache_t *)data;
+	taskqid_t id = 0;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+
+	/* Dynamically disabled at run time */
+	if (!(spl_kmem_cache_expire & KMC_EXPIRE_AGE))
+		return;
+
+	atomic_inc(&skc->skc_ref);
+
+	if (!(skc->skc_flags & KMC_NOMAGAZINE))
+		on_each_cpu(spl_magazine_age, skc, 1);
+
+	spl_slab_reclaim(skc);
+
+	while (!test_bit(KMC_BIT_DESTROY, &skc->skc_flags) && !id) {
+		id = taskq_dispatch_delay(
+		    spl_kmem_cache_taskq, spl_cache_age, skc, TQ_SLEEP,
+		    ddi_get_lbolt() + skc->skc_delay / 3 * HZ);
+
+		/* Destroy issued after dispatch immediately cancel it */
+		if (test_bit(KMC_BIT_DESTROY, &skc->skc_flags) && id)
+			taskq_cancel_id(spl_kmem_cache_taskq, id);
+	}
+
+	spin_lock(&skc->skc_lock);
+	skc->skc_taskqid = id;
+	spin_unlock(&skc->skc_lock);
+
+	atomic_dec(&skc->skc_ref);
+}
+
+/*
+ * Size a slab based on the size of each aligned object plus spl_kmem_obj_t.
+ * When on-slab we want to target spl_kmem_cache_obj_per_slab.  However,
+ * for very small objects we may end up with more than this so as not
+ * to waste space in the minimal allocation of a single page.  Also for
+ * very large objects we may use as few as spl_kmem_cache_obj_per_slab_min,
+ * lower than this and we will fail.
+ */
+static int
+spl_slab_size(spl_kmem_cache_t *skc, uint32_t *objs, uint32_t *size)
+{
+	uint32_t sks_size, obj_size, max_size, tgt_size, tgt_objs;
+
+	if (skc->skc_flags & KMC_OFFSLAB) {
+		tgt_objs = spl_kmem_cache_obj_per_slab;
+		tgt_size = P2ROUNDUP(sizeof (spl_kmem_slab_t), PAGE_SIZE);
+
+		if ((skc->skc_flags & KMC_KMEM) &&
+		    (spl_obj_size(skc) > (SPL_MAX_ORDER_NR_PAGES * PAGE_SIZE)))
+			return (-ENOSPC);
+	} else {
+		sks_size = spl_sks_size(skc);
+		obj_size = spl_obj_size(skc);
+		max_size = (spl_kmem_cache_max_size * 1024 * 1024);
+		tgt_size = (spl_kmem_cache_obj_per_slab * obj_size + sks_size);
+
+		/*
+		 * KMC_KMEM slabs are allocated by __get_free_pages() which
+		 * rounds up to the nearest order.  Knowing this the size
+		 * should be rounded up to the next power of two with a hard
+		 * maximum defined by the maximum allowed allocation order.
+		 */
+		if (skc->skc_flags & KMC_KMEM) {
+			max_size = SPL_MAX_ORDER_NR_PAGES * PAGE_SIZE;
+			tgt_size = MIN(max_size,
+			    PAGE_SIZE * (1 << MAX(get_order(tgt_size) - 1, 1)));
+		}
+
+		if (tgt_size <= max_size) {
+			tgt_objs = (tgt_size - sks_size) / obj_size;
+		} else {
+			tgt_objs = (max_size - sks_size) / obj_size;
+			tgt_size = (tgt_objs * obj_size) + sks_size;
+		}
+	}
+
+	if (tgt_objs == 0)
+		return (-ENOSPC);
+
+	*objs = tgt_objs;
+	*size = tgt_size;
+
+	return (0);
+}
+
+/*
+ * Make a guess at reasonable per-cpu magazine size based on the size of
+ * each object and the cost of caching N of them in each magazine.  Long
+ * term this should really adapt based on an observed usage heuristic.
+ */
+static int
+spl_magazine_size(spl_kmem_cache_t *skc)
+{
+	uint32_t obj_size = spl_obj_size(skc);
+	int size;
+
+	if (spl_kmem_cache_magazine_size > 0)
+		return (MAX(MIN(spl_kmem_cache_magazine_size, 256), 2));
+
+	/* Per-magazine sizes below assume a 4Kib page size */
+	if (obj_size > (PAGE_SIZE * 256))
+		size = 4;  /* Minimum 4Mib per-magazine */
+	else if (obj_size > (PAGE_SIZE * 32))
+		size = 16; /* Minimum 2Mib per-magazine */
+	else if (obj_size > (PAGE_SIZE))
+		size = 64; /* Minimum 256Kib per-magazine */
+	else if (obj_size > (PAGE_SIZE / 4))
+		size = 128; /* Minimum 128Kib per-magazine */
+	else
+		size = 256;
+
+	return (size);
+}
+
+/*
+ * Allocate a per-cpu magazine to associate with a specific core.
+ */
+static spl_kmem_magazine_t *
+spl_magazine_alloc(spl_kmem_cache_t *skc, int cpu)
+{
+	spl_kmem_magazine_t *skm;
+	int size = sizeof (spl_kmem_magazine_t) +
+	    sizeof (void *) * skc->skc_mag_size;
+
+	skm = kmalloc_node(size, GFP_KERNEL, cpu_to_node(cpu));
+	if (skm) {
+		skm->skm_magic = SKM_MAGIC;
+		skm->skm_avail = 0;
+		skm->skm_size = skc->skc_mag_size;
+		skm->skm_refill = skc->skc_mag_refill;
+		skm->skm_cache = skc;
+		skm->skm_age = jiffies;
+		skm->skm_cpu = cpu;
+	}
+
+	return (skm);
+}
+
+/*
+ * Free a per-cpu magazine associated with a specific core.
+ */
+static void
+spl_magazine_free(spl_kmem_magazine_t *skm)
+{
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+	ASSERT(skm->skm_avail == 0);
+	kfree(skm);
+}
+
+/*
+ * Create all pre-cpu magazines of reasonable sizes.
+ */
+static int
+spl_magazine_create(spl_kmem_cache_t *skc)
+{
+	int i;
+
+	if (skc->skc_flags & KMC_NOMAGAZINE)
+		return (0);
+
+	skc->skc_mag = kzalloc(sizeof (spl_kmem_magazine_t *) *
+	    num_possible_cpus(), kmem_flags_convert(KM_SLEEP));
+	skc->skc_mag_size = spl_magazine_size(skc);
+	skc->skc_mag_refill = (skc->skc_mag_size + 1) / 2;
+
+	for_each_possible_cpu(i) {
+		skc->skc_mag[i] = spl_magazine_alloc(skc, i);
+		if (!skc->skc_mag[i]) {
+			for (i--; i >= 0; i--)
+				spl_magazine_free(skc->skc_mag[i]);
+
+			kfree(skc->skc_mag);
+			return (-ENOMEM);
+		}
+	}
+
+	return (0);
+}
+
+/*
+ * Destroy all pre-cpu magazines.
+ */
+static void
+spl_magazine_destroy(spl_kmem_cache_t *skc)
+{
+	spl_kmem_magazine_t *skm;
+	int i;
+
+	if (skc->skc_flags & KMC_NOMAGAZINE)
+		return;
+
+	for_each_possible_cpu(i) {
+		skm = skc->skc_mag[i];
+		spl_cache_flush(skc, skm, skm->skm_avail);
+		spl_magazine_free(skm);
+	}
+
+	kfree(skc->skc_mag);
+}
+
+/*
+ * Create a object cache based on the following arguments:
+ * name		cache name
+ * size		cache object size
+ * align	cache object alignment
+ * ctor		cache object constructor
+ * dtor		cache object destructor
+ * reclaim	cache object reclaim
+ * priv		cache private data for ctor/dtor/reclaim
+ * vmp		unused must be NULL
+ * flags
+ *	KMC_NOTOUCH	Disable cache object aging (unsupported)
+ *	KMC_NODEBUG	Disable debugging (unsupported)
+ *	KMC_NOHASH      Disable hashing (unsupported)
+ *	KMC_QCACHE	Disable qcache (unsupported)
+ *	KMC_NOMAGAZINE	Enabled for kmem/vmem, Disabled for Linux slab
+ *	KMC_KMEM	Force kmem backed cache
+ *	KMC_VMEM        Force vmem backed cache
+ *	KMC_SLAB        Force Linux slab backed cache
+ *	KMC_OFFSLAB	Locate objects off the slab
+ */
+spl_kmem_cache_t *
+spl_kmem_cache_create(char *name, size_t size, size_t align,
+    spl_kmem_ctor_t ctor, spl_kmem_dtor_t dtor, spl_kmem_reclaim_t reclaim,
+    void *priv, void *vmp, int flags)
+{
+	gfp_t lflags = kmem_flags_convert(KM_SLEEP);
+	spl_kmem_cache_t *skc;
+	int rc;
+
+	/*
+	 * Unsupported flags
+	 */
+	ASSERT0(flags & KMC_NOMAGAZINE);
+	ASSERT0(flags & KMC_NOHASH);
+	ASSERT0(flags & KMC_QCACHE);
+	ASSERT(vmp == NULL);
+
+	might_sleep();
+
+	skc = kzalloc(sizeof (*skc), lflags);
+	if (skc == NULL)
+		return (NULL);
+
+	skc->skc_magic = SKC_MAGIC;
+	skc->skc_name_size = strlen(name) + 1;
+	skc->skc_name = (char *)kmalloc(skc->skc_name_size, lflags);
+	if (skc->skc_name == NULL) {
+		kfree(skc);
+		return (NULL);
+	}
+	strncpy(skc->skc_name, name, skc->skc_name_size);
+
+	skc->skc_ctor = ctor;
+	skc->skc_dtor = dtor;
+	skc->skc_reclaim = reclaim;
+	skc->skc_private = priv;
+	skc->skc_vmp = vmp;
+	skc->skc_linux_cache = NULL;
+	skc->skc_flags = flags;
+	skc->skc_obj_size = size;
+	skc->skc_obj_align = SPL_KMEM_CACHE_ALIGN;
+	skc->skc_delay = SPL_KMEM_CACHE_DELAY;
+	skc->skc_reap = SPL_KMEM_CACHE_REAP;
+	atomic_set(&skc->skc_ref, 0);
+
+	INIT_LIST_HEAD(&skc->skc_list);
+	INIT_LIST_HEAD(&skc->skc_complete_list);
+	INIT_LIST_HEAD(&skc->skc_partial_list);
+	skc->skc_emergency_tree = RB_ROOT;
+	spin_lock_init(&skc->skc_lock);
+	init_waitqueue_head(&skc->skc_waitq);
+	skc->skc_slab_fail = 0;
+	skc->skc_slab_create = 0;
+	skc->skc_slab_destroy = 0;
+	skc->skc_slab_total = 0;
+	skc->skc_slab_alloc = 0;
+	skc->skc_slab_max = 0;
+	skc->skc_obj_total = 0;
+	skc->skc_obj_alloc = 0;
+	skc->skc_obj_max = 0;
+	skc->skc_obj_deadlock = 0;
+	skc->skc_obj_emergency = 0;
+	skc->skc_obj_emergency_max = 0;
+
+	/*
+	 * Verify the requested alignment restriction is sane.
+	 */
+	if (align) {
+		VERIFY(ISP2(align));
+		VERIFY3U(align, >=, SPL_KMEM_CACHE_ALIGN);
+		VERIFY3U(align, <=, PAGE_SIZE);
+		skc->skc_obj_align = align;
+	}
+
+	/*
+	 * When no specific type of slab is requested (kmem, vmem, or
+	 * linuxslab) then select a cache type based on the object size
+	 * and default tunables.
+	 */
+	if (!(skc->skc_flags & (KMC_KMEM | KMC_VMEM | KMC_SLAB))) {
+
+		/*
+		 * Objects smaller than spl_kmem_cache_slab_limit can
+		 * use the Linux slab for better space-efficiency.  By
+		 * default this functionality is disabled until its
+		 * performance characteristics are fully understood.
+		 */
+		if (spl_kmem_cache_slab_limit &&
+		    size <= (size_t)spl_kmem_cache_slab_limit)
+			skc->skc_flags |= KMC_SLAB;
+
+		/*
+		 * Small objects, less than spl_kmem_cache_kmem_limit per
+		 * object should use kmem because their slabs are small.
+		 */
+		else if (spl_obj_size(skc) <= spl_kmem_cache_kmem_limit)
+			skc->skc_flags |= KMC_KMEM;
+
+		/*
+		 * All other objects are considered large and are placed
+		 * on vmem backed slabs.
+		 */
+		else
+			skc->skc_flags |= KMC_VMEM;
+	}
+
+	/*
+	 * Given the type of slab allocate the required resources.
+	 */
+	if (skc->skc_flags & (KMC_KMEM | KMC_VMEM)) {
+		rc = spl_slab_size(skc,
+		    &skc->skc_slab_objs, &skc->skc_slab_size);
+		if (rc)
+			goto out;
+
+		rc = spl_magazine_create(skc);
+		if (rc)
+			goto out;
+	} else {
+		unsigned long slabflags = 0;
+
+		if (size > (SPL_MAX_KMEM_ORDER_NR_PAGES * PAGE_SIZE)) {
+			rc = EINVAL;
+			goto out;
+		}
+
+#if defined(SLAB_USERCOPY)
+		/*
+		 * Required for PAX-enabled kernels if the slab is to be
+		 * used for coping between user and kernel space.
+		 */
+		slabflags |= SLAB_USERCOPY;
+#endif
+
+#if defined(HAVE_KMEM_CACHE_CREATE_USERCOPY)
+	/*
+	 * Newer grsec patchset uses kmem_cache_create_usercopy()
+	 * instead of SLAB_USERCOPY flag
+	 */
+	skc->skc_linux_cache = kmem_cache_create_usercopy(
+	    skc->skc_name, size, align, slabflags, 0, size, NULL);
+#else
+	skc->skc_linux_cache = kmem_cache_create(
+	    skc->skc_name, size, align, slabflags, NULL);
+#endif
+		if (skc->skc_linux_cache == NULL) {
+			rc = ENOMEM;
+			goto out;
+		}
+
+#if defined(HAVE_KMEM_CACHE_ALLOCFLAGS)
+		skc->skc_linux_cache->allocflags |= __GFP_COMP;
+#elif defined(HAVE_KMEM_CACHE_GFPFLAGS)
+		skc->skc_linux_cache->gfpflags |= __GFP_COMP;
+#endif
+		skc->skc_flags |= KMC_NOMAGAZINE;
+	}
+
+	if (spl_kmem_cache_expire & KMC_EXPIRE_AGE)
+		skc->skc_taskqid = taskq_dispatch_delay(spl_kmem_cache_taskq,
+		    spl_cache_age, skc, TQ_SLEEP,
+		    ddi_get_lbolt() + skc->skc_delay / 3 * HZ);
+
+	down_write(&spl_kmem_cache_sem);
+	list_add_tail(&skc->skc_list, &spl_kmem_cache_list);
+	up_write(&spl_kmem_cache_sem);
+
+	return (skc);
+out:
+	kfree(skc->skc_name);
+	kfree(skc);
+	return (NULL);
+}
+EXPORT_SYMBOL(spl_kmem_cache_create);
+
+/*
+ * Register a move callback for cache defragmentation.
+ * XXX: Unimplemented but harmless to stub out for now.
+ */
+void
+spl_kmem_cache_set_move(spl_kmem_cache_t *skc,
+    kmem_cbrc_t (move)(void *, void *, size_t, void *))
+{
+	ASSERT(move != NULL);
+}
+EXPORT_SYMBOL(spl_kmem_cache_set_move);
+
+/*
+ * Destroy a cache and all objects associated with the cache.
+ */
+void
+spl_kmem_cache_destroy(spl_kmem_cache_t *skc)
+{
+	DECLARE_WAIT_QUEUE_HEAD(wq);
+	taskqid_t id;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(skc->skc_flags & (KMC_KMEM | KMC_VMEM | KMC_SLAB));
+
+	down_write(&spl_kmem_cache_sem);
+	list_del_init(&skc->skc_list);
+	up_write(&spl_kmem_cache_sem);
+
+	/* Cancel any and wait for any pending delayed tasks */
+	VERIFY(!test_and_set_bit(KMC_BIT_DESTROY, &skc->skc_flags));
+
+	spin_lock(&skc->skc_lock);
+	id = skc->skc_taskqid;
+	spin_unlock(&skc->skc_lock);
+
+	taskq_cancel_id(spl_kmem_cache_taskq, id);
+
+	/*
+	 * Wait until all current callers complete, this is mainly
+	 * to catch the case where a low memory situation triggers a
+	 * cache reaping action which races with this destroy.
+	 */
+	wait_event(wq, atomic_read(&skc->skc_ref) == 0);
+
+	if (skc->skc_flags & (KMC_KMEM | KMC_VMEM)) {
+		spl_magazine_destroy(skc);
+		spl_slab_reclaim(skc);
+	} else {
+		ASSERT(skc->skc_flags & KMC_SLAB);
+		kmem_cache_destroy(skc->skc_linux_cache);
+	}
+
+	spin_lock(&skc->skc_lock);
+
+	/*
+	 * Validate there are no objects in use and free all the
+	 * spl_kmem_slab_t, spl_kmem_obj_t, and object buffers.
+	 */
+	ASSERT3U(skc->skc_slab_alloc, ==, 0);
+	ASSERT3U(skc->skc_obj_alloc, ==, 0);
+	ASSERT3U(skc->skc_slab_total, ==, 0);
+	ASSERT3U(skc->skc_obj_total, ==, 0);
+	ASSERT3U(skc->skc_obj_emergency, ==, 0);
+	ASSERT(list_empty(&skc->skc_complete_list));
+
+	spin_unlock(&skc->skc_lock);
+
+	kfree(skc->skc_name);
+	kfree(skc);
+}
+EXPORT_SYMBOL(spl_kmem_cache_destroy);
+
+/*
+ * Allocate an object from a slab attached to the cache.  This is used to
+ * repopulate the per-cpu magazine caches in batches when they run low.
+ */
+static void *
+spl_cache_obj(spl_kmem_cache_t *skc, spl_kmem_slab_t *sks)
+{
+	spl_kmem_obj_t *sko;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(sks->sks_magic == SKS_MAGIC);
+
+	sko = list_entry(sks->sks_free_list.next, spl_kmem_obj_t, sko_list);
+	ASSERT(sko->sko_magic == SKO_MAGIC);
+	ASSERT(sko->sko_addr != NULL);
+
+	/* Remove from sks_free_list */
+	list_del_init(&sko->sko_list);
+
+	sks->sks_age = jiffies;
+	sks->sks_ref++;
+	skc->skc_obj_alloc++;
+
+	/* Track max obj usage statistics */
+	if (skc->skc_obj_alloc > skc->skc_obj_max)
+		skc->skc_obj_max = skc->skc_obj_alloc;
+
+	/* Track max slab usage statistics */
+	if (sks->sks_ref == 1) {
+		skc->skc_slab_alloc++;
+
+		if (skc->skc_slab_alloc > skc->skc_slab_max)
+			skc->skc_slab_max = skc->skc_slab_alloc;
+	}
+
+	return (sko->sko_addr);
+}
+
+/*
+ * Generic slab allocation function to run by the global work queues.
+ * It is responsible for allocating a new slab, linking it in to the list
+ * of partial slabs, and then waking any waiters.
+ */
+static int
+__spl_cache_grow(spl_kmem_cache_t *skc, int flags)
+{
+	spl_kmem_slab_t *sks;
+
+	fstrans_cookie_t cookie = spl_fstrans_mark();
+	sks = spl_slab_alloc(skc, flags);
+	spl_fstrans_unmark(cookie);
+
+	spin_lock(&skc->skc_lock);
+	if (sks) {
+		skc->skc_slab_total++;
+		skc->skc_obj_total += sks->sks_objs;
+		list_add_tail(&sks->sks_list, &skc->skc_partial_list);
+
+		smp_mb__before_atomic();
+		clear_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags);
+		smp_mb__after_atomic();
+		wake_up_all(&skc->skc_waitq);
+	}
+	spin_unlock(&skc->skc_lock);
+
+	return (sks == NULL ? -ENOMEM : 0);
+}
+
+static void
+spl_cache_grow_work(void *data)
+{
+	spl_kmem_alloc_t *ska = (spl_kmem_alloc_t *)data;
+	spl_kmem_cache_t *skc = ska->ska_cache;
+
+	(void) __spl_cache_grow(skc, ska->ska_flags);
+
+	atomic_dec(&skc->skc_ref);
+	smp_mb__before_atomic();
+	clear_bit(KMC_BIT_GROWING, &skc->skc_flags);
+	smp_mb__after_atomic();
+
+	kfree(ska);
+}
+
+/*
+ * Returns non-zero when a new slab should be available.
+ */
+static int
+spl_cache_grow_wait(spl_kmem_cache_t *skc)
+{
+	return (!test_bit(KMC_BIT_GROWING, &skc->skc_flags));
+}
+
+/*
+ * No available objects on any slabs, create a new slab.  Note that this
+ * functionality is disabled for KMC_SLAB caches which are backed by the
+ * Linux slab.
+ */
+static int
+spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj)
+{
+	int remaining, rc = 0;
+
+	ASSERT0(flags & ~KM_PUBLIC_MASK);
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT((skc->skc_flags & KMC_SLAB) == 0);
+	might_sleep();
+	*obj = NULL;
+
+	/*
+	 * Before allocating a new slab wait for any reaping to complete and
+	 * then return so the local magazine can be rechecked for new objects.
+	 */
+	if (test_bit(KMC_BIT_REAPING, &skc->skc_flags)) {
+		rc = spl_wait_on_bit(&skc->skc_flags, KMC_BIT_REAPING,
+		    TASK_UNINTERRUPTIBLE);
+		return (rc ? rc : -EAGAIN);
+	}
+
+	/*
+	 * To reduce the overhead of context switch and improve NUMA locality,
+	 * it tries to allocate a new slab in the current process context with
+	 * KM_NOSLEEP flag. If it fails, it will launch a new taskq to do the
+	 * allocation.
+	 *
+	 * However, this can't be applied to KVM_VMEM due to a bug that
+	 * __vmalloc() doesn't honor gfp flags in page table allocation.
+	 */
+	if (!(skc->skc_flags & KMC_VMEM)) {
+		rc = __spl_cache_grow(skc, flags | KM_NOSLEEP);
+		if (rc == 0)
+			return (0);
+	}
+
+	/*
+	 * This is handled by dispatching a work request to the global work
+	 * queue.  This allows us to asynchronously allocate a new slab while
+	 * retaining the ability to safely fall back to a smaller synchronous
+	 * allocations to ensure forward progress is always maintained.
+	 */
+	if (test_and_set_bit(KMC_BIT_GROWING, &skc->skc_flags) == 0) {
+		spl_kmem_alloc_t *ska;
+
+		ska = kmalloc(sizeof (*ska), kmem_flags_convert(flags));
+		if (ska == NULL) {
+			clear_bit_unlock(KMC_BIT_GROWING, &skc->skc_flags);
+			smp_mb__after_atomic();
+			wake_up_all(&skc->skc_waitq);
+			return (-ENOMEM);
+		}
+
+		atomic_inc(&skc->skc_ref);
+		ska->ska_cache = skc;
+		ska->ska_flags = flags;
+		taskq_init_ent(&ska->ska_tqe);
+		taskq_dispatch_ent(spl_kmem_cache_taskq,
+		    spl_cache_grow_work, ska, 0, &ska->ska_tqe);
+	}
+
+	/*
+	 * The goal here is to only detect the rare case where a virtual slab
+	 * allocation has deadlocked.  We must be careful to minimize the use
+	 * of emergency objects which are more expensive to track.  Therefore,
+	 * we set a very long timeout for the asynchronous allocation and if
+	 * the timeout is reached the cache is flagged as deadlocked.  From
+	 * this point only new emergency objects will be allocated until the
+	 * asynchronous allocation completes and clears the deadlocked flag.
+	 */
+	if (test_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags)) {
+		rc = spl_emergency_alloc(skc, flags, obj);
+	} else {
+		remaining = wait_event_timeout(skc->skc_waitq,
+		    spl_cache_grow_wait(skc), HZ / 10);
+
+		if (!remaining) {
+			spin_lock(&skc->skc_lock);
+			if (test_bit(KMC_BIT_GROWING, &skc->skc_flags)) {
+				set_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags);
+				skc->skc_obj_deadlock++;
+			}
+			spin_unlock(&skc->skc_lock);
+		}
+
+		rc = -ENOMEM;
+	}
+
+	return (rc);
+}
+
+/*
+ * Refill a per-cpu magazine with objects from the slabs for this cache.
+ * Ideally the magazine can be repopulated using existing objects which have
+ * been released, however if we are unable to locate enough free objects new
+ * slabs of objects will be created.  On success NULL is returned, otherwise
+ * the address of a single emergency object is returned for use by the caller.
+ */
+static void *
+spl_cache_refill(spl_kmem_cache_t *skc, spl_kmem_magazine_t *skm, int flags)
+{
+	spl_kmem_slab_t *sks;
+	int count = 0, rc, refill;
+	void *obj = NULL;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+
+	refill = MIN(skm->skm_refill, skm->skm_size - skm->skm_avail);
+	spin_lock(&skc->skc_lock);
+
+	while (refill > 0) {
+		/* No slabs available we may need to grow the cache */
+		if (list_empty(&skc->skc_partial_list)) {
+			spin_unlock(&skc->skc_lock);
+
+			local_irq_enable();
+			rc = spl_cache_grow(skc, flags, &obj);
+			local_irq_disable();
+
+			/* Emergency object for immediate use by caller */
+			if (rc == 0 && obj != NULL)
+				return (obj);
+
+			if (rc)
+				goto out;
+
+			/* Rescheduled to different CPU skm is not local */
+			if (skm != skc->skc_mag[smp_processor_id()])
+				goto out;
+
+			/*
+			 * Potentially rescheduled to the same CPU but
+			 * allocations may have occurred from this CPU while
+			 * we were sleeping so recalculate max refill.
+			 */
+			refill = MIN(refill, skm->skm_size - skm->skm_avail);
+
+			spin_lock(&skc->skc_lock);
+			continue;
+		}
+
+		/* Grab the next available slab */
+		sks = list_entry((&skc->skc_partial_list)->next,
+		    spl_kmem_slab_t, sks_list);
+		ASSERT(sks->sks_magic == SKS_MAGIC);
+		ASSERT(sks->sks_ref < sks->sks_objs);
+		ASSERT(!list_empty(&sks->sks_free_list));
+
+		/*
+		 * Consume as many objects as needed to refill the requested
+		 * cache.  We must also be careful not to overfill it.
+		 */
+		while (sks->sks_ref < sks->sks_objs && refill-- > 0 &&
+		    ++count) {
+			ASSERT(skm->skm_avail < skm->skm_size);
+			ASSERT(count < skm->skm_size);
+			skm->skm_objs[skm->skm_avail++] =
+			    spl_cache_obj(skc, sks);
+		}
+
+		/* Move slab to skc_complete_list when full */
+		if (sks->sks_ref == sks->sks_objs) {
+			list_del(&sks->sks_list);
+			list_add(&sks->sks_list, &skc->skc_complete_list);
+		}
+	}
+
+	spin_unlock(&skc->skc_lock);
+out:
+	return (NULL);
+}
+
+/*
+ * Release an object back to the slab from which it came.
+ */
+static void
+spl_cache_shrink(spl_kmem_cache_t *skc, void *obj)
+{
+	spl_kmem_slab_t *sks = NULL;
+	spl_kmem_obj_t *sko = NULL;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+
+	sko = spl_sko_from_obj(skc, obj);
+	ASSERT(sko->sko_magic == SKO_MAGIC);
+	sks = sko->sko_slab;
+	ASSERT(sks->sks_magic == SKS_MAGIC);
+	ASSERT(sks->sks_cache == skc);
+	list_add(&sko->sko_list, &sks->sks_free_list);
+
+	sks->sks_age = jiffies;
+	sks->sks_ref--;
+	skc->skc_obj_alloc--;
+
+	/*
+	 * Move slab to skc_partial_list when no longer full.  Slabs
+	 * are added to the head to keep the partial list is quasi-full
+	 * sorted order.  Fuller at the head, emptier at the tail.
+	 */
+	if (sks->sks_ref == (sks->sks_objs - 1)) {
+		list_del(&sks->sks_list);
+		list_add(&sks->sks_list, &skc->skc_partial_list);
+	}
+
+	/*
+	 * Move empty slabs to the end of the partial list so
+	 * they can be easily found and freed during reclamation.
+	 */
+	if (sks->sks_ref == 0) {
+		list_del(&sks->sks_list);
+		list_add_tail(&sks->sks_list, &skc->skc_partial_list);
+		skc->skc_slab_alloc--;
+	}
+}
+
+/*
+ * Allocate an object from the per-cpu magazine, or if the magazine
+ * is empty directly allocate from a slab and repopulate the magazine.
+ */
+void *
+spl_kmem_cache_alloc(spl_kmem_cache_t *skc, int flags)
+{
+	spl_kmem_magazine_t *skm;
+	void *obj = NULL;
+
+	ASSERT0(flags & ~KM_PUBLIC_MASK);
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));
+
+	/*
+	 * Allocate directly from a Linux slab.  All optimizations are left
+	 * to the underlying cache we only need to guarantee that KM_SLEEP
+	 * callers will never fail.
+	 */
+	if (skc->skc_flags & KMC_SLAB) {
+		struct kmem_cache *slc = skc->skc_linux_cache;
+		do {
+			obj = kmem_cache_alloc(slc, kmem_flags_convert(flags));
+		} while ((obj == NULL) && !(flags & KM_NOSLEEP));
+
+		goto ret;
+	}
+
+	local_irq_disable();
+
+restart:
+	/*
+	 * Safe to update per-cpu structure without lock, but
+	 * in the restart case we must be careful to reacquire
+	 * the local magazine since this may have changed
+	 * when we need to grow the cache.
+	 */
+	skm = skc->skc_mag[smp_processor_id()];
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+
+	if (likely(skm->skm_avail)) {
+		/* Object available in CPU cache, use it */
+		obj = skm->skm_objs[--skm->skm_avail];
+		skm->skm_age = jiffies;
+	} else {
+		obj = spl_cache_refill(skc, skm, flags);
+		if ((obj == NULL) && !(flags & KM_NOSLEEP))
+			goto restart;
+
+		local_irq_enable();
+		goto ret;
+	}
+
+	local_irq_enable();
+	ASSERT(obj);
+	ASSERT(IS_P2ALIGNED(obj, skc->skc_obj_align));
+
+ret:
+	/* Pre-emptively migrate object to CPU L1 cache */
+	if (obj) {
+		if (obj && skc->skc_ctor)
+			skc->skc_ctor(obj, skc->skc_private, flags);
+		else
+			prefetchw(obj);
+	}
+
+	return (obj);
+}
+EXPORT_SYMBOL(spl_kmem_cache_alloc);
+
+/*
+ * Free an object back to the local per-cpu magazine, there is no
+ * guarantee that this is the same magazine the object was originally
+ * allocated from.  We may need to flush entire from the magazine
+ * back to the slabs to make space.
+ */
+void
+spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
+{
+	spl_kmem_magazine_t *skm;
+	unsigned long flags;
+	int do_reclaim = 0;
+	int do_emergency = 0;
+
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));
+
+	/*
+	 * Run the destructor
+	 */
+	if (skc->skc_dtor)
+		skc->skc_dtor(obj, skc->skc_private);
+
+	/*
+	 * Free the object from the Linux underlying Linux slab.
+	 */
+	if (skc->skc_flags & KMC_SLAB) {
+		kmem_cache_free(skc->skc_linux_cache, obj);
+		return;
+	}
+
+	/*
+	 * While a cache has outstanding emergency objects all freed objects
+	 * must be checked.  However, since emergency objects will never use
+	 * a virtual address these objects can be safely excluded as an
+	 * optimization.
+	 */
+	if (!is_vmalloc_addr(obj)) {
+		spin_lock(&skc->skc_lock);
+		do_emergency = (skc->skc_obj_emergency > 0);
+		spin_unlock(&skc->skc_lock);
+
+		if (do_emergency && (spl_emergency_free(skc, obj) == 0))
+			return;
+	}
+
+	local_irq_save(flags);
+
+	/*
+	 * Safe to update per-cpu structure without lock, but
+	 * no remote memory allocation tracking is being performed
+	 * it is entirely possible to allocate an object from one
+	 * CPU cache and return it to another.
+	 */
+	skm = skc->skc_mag[smp_processor_id()];
+	ASSERT(skm->skm_magic == SKM_MAGIC);
+
+	/*
+	 * Per-CPU cache full, flush it to make space for this object,
+	 * this may result in an empty slab which can be reclaimed once
+	 * interrupts are re-enabled.
+	 */
+	if (unlikely(skm->skm_avail >= skm->skm_size)) {
+		spl_cache_flush(skc, skm, skm->skm_refill);
+		do_reclaim = 1;
+	}
+
+	/* Available space in cache, use it */
+	skm->skm_objs[skm->skm_avail++] = obj;
+
+	local_irq_restore(flags);
+
+	if (do_reclaim)
+		spl_slab_reclaim(skc);
+}
+EXPORT_SYMBOL(spl_kmem_cache_free);
+
+/*
+ * The generic shrinker function for all caches.  Under Linux a shrinker
+ * may not be tightly coupled with a slab cache.  In fact Linux always
+ * systematically tries calling all registered shrinker callbacks which
+ * report that they contain unused objects.  Because of this we only
+ * register one shrinker function in the shim layer for all slab caches.
+ * We always attempt to shrink all caches when this generic shrinker
+ * is called.
+ *
+ * If sc->nr_to_scan is zero, the caller is requesting a query of the
+ * number of objects which can potentially be freed.  If it is nonzero,
+ * the request is to free that many objects.
+ *
+ * Linux kernels >= 3.12 have the count_objects and scan_objects callbacks
+ * in struct shrinker and also require the shrinker to return the number
+ * of objects freed.
+ *
+ * Older kernels require the shrinker to return the number of freeable
+ * objects following the freeing of nr_to_free.
+ *
+ * Linux semantics differ from those under Solaris, which are to
+ * free all available objects which may (and probably will) be more
+ * objects than the requested nr_to_scan.
+ */
+static spl_shrinker_t
+__spl_kmem_cache_generic_shrinker(struct shrinker *shrink,
+    struct shrink_control *sc)
+{
+	spl_kmem_cache_t *skc;
+	int alloc = 0;
+
+	/*
+	 * No shrinking in a transaction context.  Can cause deadlocks.
+	 */
+	if (sc->nr_to_scan && spl_fstrans_check())
+		return (SHRINK_STOP);
+
+	down_read(&spl_kmem_cache_sem);
+	list_for_each_entry(skc, &spl_kmem_cache_list, skc_list) {
+		if (sc->nr_to_scan) {
+#ifdef HAVE_SPLIT_SHRINKER_CALLBACK
+			uint64_t oldalloc = skc->skc_obj_alloc;
+			spl_kmem_cache_reap_now(skc,
+			    MAX(sc->nr_to_scan>>fls64(skc->skc_slab_objs), 1));
+			if (oldalloc > skc->skc_obj_alloc)
+				alloc += oldalloc - skc->skc_obj_alloc;
+#else
+			spl_kmem_cache_reap_now(skc,
+			    MAX(sc->nr_to_scan>>fls64(skc->skc_slab_objs), 1));
+			alloc += skc->skc_obj_alloc;
+#endif /* HAVE_SPLIT_SHRINKER_CALLBACK */
+		} else {
+			/* Request to query number of freeable objects */
+			alloc += skc->skc_obj_alloc;
+		}
+	}
+	up_read(&spl_kmem_cache_sem);
+
+	/*
+	 * When KMC_RECLAIM_ONCE is set allow only a single reclaim pass.
+	 * This functionality only exists to work around a rare issue where
+	 * shrink_slabs() is repeatedly invoked by many cores causing the
+	 * system to thrash.
+	 */
+	if ((spl_kmem_cache_reclaim & KMC_RECLAIM_ONCE) && sc->nr_to_scan)
+		return (SHRINK_STOP);
+
+	return (MAX(alloc, 0));
+}
+
+SPL_SHRINKER_CALLBACK_WRAPPER(spl_kmem_cache_generic_shrinker);
+
+/*
+ * Call the registered reclaim function for a cache.  Depending on how
+ * many and which objects are released it may simply repopulate the
+ * local magazine which will then need to age-out.  Objects which cannot
+ * fit in the magazine we will be released back to their slabs which will
+ * also need to age out before being release.  This is all just best
+ * effort and we do not want to thrash creating and destroying slabs.
+ */
+void
+spl_kmem_cache_reap_now(spl_kmem_cache_t *skc, int count)
+{
+	ASSERT(skc->skc_magic == SKC_MAGIC);
+	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));
+
+	atomic_inc(&skc->skc_ref);
+
+	/*
+	 * Execute the registered reclaim callback if it exists.
+	 */
+	if (skc->skc_flags & KMC_SLAB) {
+		if (skc->skc_reclaim)
+			skc->skc_reclaim(skc->skc_private);
+		goto out;
+	}
+
+	/*
+	 * Prevent concurrent cache reaping when contended.
+	 */
+	if (test_and_set_bit(KMC_BIT_REAPING, &skc->skc_flags))
+		goto out;
+
+	/*
+	 * When a reclaim function is available it may be invoked repeatedly
+	 * until at least a single slab can be freed.  This ensures that we
+	 * do free memory back to the system.  This helps minimize the chance
+	 * of an OOM event when the bulk of memory is used by the slab.
+	 *
+	 * When free slabs are already available the reclaim callback will be
+	 * skipped.  Additionally, if no forward progress is detected despite
+	 * a reclaim function the cache will be skipped to avoid deadlock.
+	 *
+	 * Longer term this would be the correct place to add the code which
+	 * repacks the slabs in order minimize fragmentation.
+	 */
+	if (skc->skc_reclaim) {
+		uint64_t objects = UINT64_MAX;
+		int do_reclaim;
+
+		do {
+			spin_lock(&skc->skc_lock);
+			do_reclaim =
+			    (skc->skc_slab_total > 0) &&
+			    ((skc->skc_slab_total-skc->skc_slab_alloc) == 0) &&
+			    (skc->skc_obj_alloc < objects);
+
+			objects = skc->skc_obj_alloc;
+			spin_unlock(&skc->skc_lock);
+
+			if (do_reclaim)
+				skc->skc_reclaim(skc->skc_private);
+
+		} while (do_reclaim);
+	}
+
+	/* Reclaim from the magazine and free all now empty slabs. */
+	if (spl_kmem_cache_expire & KMC_EXPIRE_MEM) {
+		spl_kmem_magazine_t *skm;
+		unsigned long irq_flags;
+
+		local_irq_save(irq_flags);
+		skm = skc->skc_mag[smp_processor_id()];
+		spl_cache_flush(skc, skm, skm->skm_avail);
+		local_irq_restore(irq_flags);
+	}
+
+	spl_slab_reclaim(skc);
+	clear_bit_unlock(KMC_BIT_REAPING, &skc->skc_flags);
+	smp_mb__after_atomic();
+	wake_up_bit(&skc->skc_flags, KMC_BIT_REAPING);
+out:
+	atomic_dec(&skc->skc_ref);
+}
+EXPORT_SYMBOL(spl_kmem_cache_reap_now);
+
+/*
+ * Reap all free slabs from all registered caches.
+ */
+void
+spl_kmem_reap(void)
+{
+	struct shrink_control sc;
+
+	sc.nr_to_scan = KMC_REAP_CHUNK;
+	sc.gfp_mask = GFP_KERNEL;
+
+	(void) __spl_kmem_cache_generic_shrinker(NULL, &sc);
+}
+EXPORT_SYMBOL(spl_kmem_reap);
+
+int
+spl_kmem_cache_init(void)
+{
+	init_rwsem(&spl_kmem_cache_sem);
+	INIT_LIST_HEAD(&spl_kmem_cache_list);
+	spl_kmem_cache_taskq = taskq_create("spl_kmem_cache",
+	    spl_kmem_cache_kmem_threads, maxclsyspri,
+	    spl_kmem_cache_kmem_threads * 8, INT_MAX,
+	    TASKQ_PREPOPULATE | TASKQ_DYNAMIC);
+	spl_register_shrinker(&spl_kmem_cache_shrinker);
+
+	return (0);
+}
+
+void
+spl_kmem_cache_fini(void)
+{
+	spl_unregister_shrinker(&spl_kmem_cache_shrinker);
+	taskq_destroy(spl_kmem_cache_taskq);
+}