Combine OS-independent ABD Code into Common Source File

Reorganizing ABD code base so OS-independent ABD code has been placed
into a common abd.c file. OS-dependent ABD code has been left in each
OS's ABD source files, and these source files have been renamed to
abd_os.

The OS-independent ABD code is now under:
module/zfs/abd.c
With the OS-dependent code in:
module/os/linux/zfs/abd_os.c
module/os/freebsd/zfs/abd_os.c

Reviewed-by: Matthew Ahrens <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Brian Atkinson <[email protected]>
Closes #10293 

1 files changed, 0 insertions, 1616 deletions

diff --git a/module/os/linux/zfs/abd.c b/module/os/linux/zfs/abd.c
deleted file mode 100644
index bc6f81000..000000000
--- a/module/os/linux/zfs/abd.c
+++ /dev/null
@@ -1,1616 +0,0 @@
-/*
- * CDDL HEADER START
- *
- * The contents of this file are subject to the terms of the
- * Common Development and Distribution License (the "License").
- * You may not use this file except in compliance with the License.
- *
- * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
- * or http://www.opensolaris.org/os/licensing.
- * See the License for the specific language governing permissions
- * and limitations under the License.
- *
- * When distributing Covered Code, include this CDDL HEADER in each
- * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
- * If applicable, add the following below this CDDL HEADER, with the
- * fields enclosed by brackets "[]" replaced with your own identifying
- * information: Portions Copyright [yyyy] [name of copyright owner]
- *
- * CDDL HEADER END
- */
-/*
- * Copyright (c) 2014 by Chunwei Chen. All rights reserved.
- * Copyright (c) 2019 by Delphix. All rights reserved.
- */
-
-/*
- * ARC buffer data (ABD).
- *
- * ABDs are an abstract data structure for the ARC which can use two
- * different ways of storing the underlying data:
- *
- * (a) Linear buffer. In this case, all the data in the ABD is stored in one
- *     contiguous buffer in memory (from a zio_[data_]buf_* kmem cache).
- *
- *         +-------------------+
- *         | ABD (linear)      |
- *         |   abd_flags = ... |
- *         |   abd_size = ...  |     +--------------------------------+
- *         |   abd_buf ------------->| raw buffer of size abd_size    |
- *         +-------------------+     +--------------------------------+
- *              no abd_chunks
- *
- * (b) Scattered buffer. In this case, the data in the ABD is split into
- *     equal-sized chunks (from the abd_chunk_cache kmem_cache), with pointers
- *     to the chunks recorded in an array at the end of the ABD structure.
- *
- *         +-------------------+
- *         | ABD (scattered)   |
- *         |   abd_flags = ... |
- *         |   abd_size = ...  |
- *         |   abd_offset = 0  |                           +-----------+
- *         |   abd_chunks[0] ----------------------------->| chunk 0   |
- *         |   abd_chunks[1] ---------------------+        +-----------+
- *         |   ...             |                  |        +-----------+
- *         |   abd_chunks[N-1] ---------+         +------->| chunk 1   |
- *         +-------------------+        |                  +-----------+
- *                                      |                      ...
- *                                      |                  +-----------+
- *                                      +----------------->| chunk N-1 |
- *                                                         +-----------+
- *
- * Linear buffers act exactly like normal buffers and are always mapped into the
- * kernel's virtual memory space, while scattered ABD data chunks are allocated
- * as physical pages and then mapped in only while they are actually being
- * accessed through one of the abd_* library functions. Using scattered ABDs
- * provides several benefits:
- *
- *  (1) They avoid use of kmem_*, preventing performance problems where running
- *      kmem_reap on very large memory systems never finishes and causes
- *      constant TLB shootdowns.
- *
- *  (2) Fragmentation is less of an issue since when we are at the limit of
- *      allocatable space, we won't have to search around for a long free
- *      hole in the VA space for large ARC allocations. Each chunk is mapped in
- *      individually, so even if we are using HIGHMEM (see next point) we
- *      wouldn't need to worry about finding a contiguous address range.
- *
- *  (3) If we are not using HIGHMEM, then all physical memory is always
- *      mapped into the kernel's address space, so we also avoid the map /
- *      unmap costs on each ABD access.
- *
- * If we are not using HIGHMEM, scattered buffers which have only one chunk
- * can be treated as linear buffers, because they are contiguous in the
- * kernel's virtual address space.  See abd_alloc_pages() for details.
- *
- * It is possible to make all ABDs linear by setting zfs_abd_scatter_enabled to
- * B_FALSE.
- *
- * In addition to directly allocating a linear or scattered ABD, it is also
- * possible to create an ABD by requesting the "sub-ABD" starting at an offset
- * within an existing ABD. In linear buffers this is simple (set abd_buf of
- * the new ABD to the starting point within the original raw buffer), but
- * scattered ABDs are a little more complex. The new ABD makes a copy of the
- * relevant abd_chunks pointers (but not the underlying data). However, to
- * provide arbitrary rather than only chunk-aligned starting offsets, it also
- * tracks an abd_offset field which represents the starting point of the data
- * within the first chunk in abd_chunks. For both linear and scattered ABDs,
- * creating an offset ABD marks the original ABD as the offset's parent, and the
- * original ABD's abd_children refcount is incremented. This data allows us to
- * ensure the root ABD isn't deleted before its children.
- *
- * Most consumers should never need to know what type of ABD they're using --
- * the ABD public API ensures that it's possible to transparently switch from
- * using a linear ABD to a scattered one when doing so would be beneficial.
- *
- * If you need to use the data within an ABD directly, if you know it's linear
- * (because you allocated it) you can use abd_to_buf() to access the underlying
- * raw buffer. Otherwise, you should use one of the abd_borrow_buf* functions
- * which will allocate a raw buffer if necessary. Use the abd_return_buf*
- * functions to return any raw buffers that are no longer necessary when you're
- * done using them.
- *
- * There are a variety of ABD APIs that implement basic buffer operations:
- * compare, copy, read, write, and fill with zeroes. If you need a custom
- * function which progressively accesses the whole ABD, use the abd_iterate_*
- * functions.
- */
-
-#include <sys/abd.h>
-#include <sys/param.h>
-#include <sys/zio.h>
-#include <sys/zfs_context.h>
-#include <sys/zfs_znode.h>
-#ifdef _KERNEL
-#include <linux/scatterlist.h>
-#include <linux/kmap_compat.h>
-#else
-#define	MAX_ORDER	1
-#endif
-
-typedef struct abd_stats {
-	kstat_named_t abdstat_struct_size;
-	kstat_named_t abdstat_linear_cnt;
-	kstat_named_t abdstat_linear_data_size;
-	kstat_named_t abdstat_scatter_cnt;
-	kstat_named_t abdstat_scatter_data_size;
-	kstat_named_t abdstat_scatter_chunk_waste;
-	kstat_named_t abdstat_scatter_orders[MAX_ORDER];
-	kstat_named_t abdstat_scatter_page_multi_chunk;
-	kstat_named_t abdstat_scatter_page_multi_zone;
-	kstat_named_t abdstat_scatter_page_alloc_retry;
-	kstat_named_t abdstat_scatter_sg_table_retry;
-} abd_stats_t;
-
-static abd_stats_t abd_stats = {
-	/* Amount of memory occupied by all of the abd_t struct allocations */
-	{ "struct_size",			KSTAT_DATA_UINT64 },
-	/*
-	 * The number of linear ABDs which are currently allocated, excluding
-	 * ABDs which don't own their data (for instance the ones which were
-	 * allocated through abd_get_offset() and abd_get_from_buf()). If an
-	 * ABD takes ownership of its buf then it will become tracked.
-	 */
-	{ "linear_cnt",				KSTAT_DATA_UINT64 },
-	/* Amount of data stored in all linear ABDs tracked by linear_cnt */
-	{ "linear_data_size",			KSTAT_DATA_UINT64 },
-	/*
-	 * The number of scatter ABDs which are currently allocated, excluding
-	 * ABDs which don't own their data (for instance the ones which were
-	 * allocated through abd_get_offset()).
-	 */
-	{ "scatter_cnt",			KSTAT_DATA_UINT64 },
-	/* Amount of data stored in all scatter ABDs tracked by scatter_cnt */
-	{ "scatter_data_size",			KSTAT_DATA_UINT64 },
-	/*
-	 * The amount of space wasted at the end of the last chunk across all
-	 * scatter ABDs tracked by scatter_cnt.
-	 */
-	{ "scatter_chunk_waste",		KSTAT_DATA_UINT64 },
-	/*
-	 * The number of compound allocations of a given order.  These
-	 * allocations are spread over all currently allocated ABDs, and
-	 * act as a measure of memory fragmentation.
-	 */
-	{ { "scatter_order_N",			KSTAT_DATA_UINT64 } },
-	/*
-	 * The number of scatter ABDs which contain multiple chunks.
-	 * ABDs are preferentially allocated from the minimum number of
-	 * contiguous multi-page chunks, a single chunk is optimal.
-	 */
-	{ "scatter_page_multi_chunk",		KSTAT_DATA_UINT64 },
-	/*
-	 * The number of scatter ABDs which are split across memory zones.
-	 * ABDs are preferentially allocated using pages from a single zone.
-	 */
-	{ "scatter_page_multi_zone",		KSTAT_DATA_UINT64 },
-	/*
-	 *  The total number of retries encountered when attempting to
-	 *  allocate the pages to populate the scatter ABD.
-	 */
-	{ "scatter_page_alloc_retry",		KSTAT_DATA_UINT64 },
-	/*
-	 *  The total number of retries encountered when attempting to
-	 *  allocate the sg table for an ABD.
-	 */
-	{ "scatter_sg_table_retry",		KSTAT_DATA_UINT64 },
-};
-
-#define	ABDSTAT(stat)		(abd_stats.stat.value.ui64)
-#define	ABDSTAT_INCR(stat, val) \
-	atomic_add_64(&abd_stats.stat.value.ui64, (val))
-#define	ABDSTAT_BUMP(stat)	ABDSTAT_INCR(stat, 1)
-#define	ABDSTAT_BUMPDOWN(stat)	ABDSTAT_INCR(stat, -1)
-
-#define	ABD_SCATTER(abd)	(abd->abd_u.abd_scatter)
-#define	ABD_BUF(abd)		(abd->abd_u.abd_linear.abd_buf)
-#define	abd_for_each_sg(abd, sg, n, i)	\
-	for_each_sg(ABD_SCATTER(abd).abd_sgl, sg, n, i)
-
-/* see block comment above for description */
-int zfs_abd_scatter_enabled = B_TRUE;
-unsigned zfs_abd_scatter_max_order = MAX_ORDER - 1;
-
-/*
- * zfs_abd_scatter_min_size is the minimum allocation size to use scatter
- * ABD's.  Smaller allocations will use linear ABD's which uses
- * zio_[data_]buf_alloc().
- *
- * Scatter ABD's use at least one page each, so sub-page allocations waste
- * some space when allocated as scatter (e.g. 2KB scatter allocation wastes
- * half of each page).  Using linear ABD's for small allocations means that
- * they will be put on slabs which contain many allocations.  This can
- * improve memory efficiency, but it also makes it much harder for ARC
- * evictions to actually free pages, because all the buffers on one slab need
- * to be freed in order for the slab (and underlying pages) to be freed.
- * Typically, 512B and 1KB kmem caches have 16 buffers per slab, so it's
- * possible for them to actually waste more memory than scatter (one page per
- * buf = wasting 3/4 or 7/8th; one buf per slab = wasting 15/16th).
- *
- * Spill blocks are typically 512B and are heavily used on systems running
- * selinux with the default dnode size and the `xattr=sa` property set.
- *
- * By default we use linear allocations for 512B and 1KB, and scatter
- * allocations for larger (1.5KB and up).
- */
-int zfs_abd_scatter_min_size = 512 * 3;
-
-static kmem_cache_t *abd_cache = NULL;
-static kstat_t *abd_ksp;
-
-static inline size_t
-abd_chunkcnt_for_bytes(size_t size)
-{
-	return (P2ROUNDUP(size, PAGESIZE) / PAGESIZE);
-}
-
-#ifdef _KERNEL
-/*
- * Mark zfs data pages so they can be excluded from kernel crash dumps
- */
-#ifdef _LP64
-#define	ABD_FILE_CACHE_PAGE	0x2F5ABDF11ECAC4E
-
-static inline void
-abd_mark_zfs_page(struct page *page)
-{
-	get_page(page);
-	SetPagePrivate(page);
-	set_page_private(page, ABD_FILE_CACHE_PAGE);
-}
-
-static inline void
-abd_unmark_zfs_page(struct page *page)
-{
-	set_page_private(page, 0UL);
-	ClearPagePrivate(page);
-	put_page(page);
-}
-#else
-#define	abd_mark_zfs_page(page)
-#define	abd_unmark_zfs_page(page)
-#endif /* _LP64 */
-
-#ifndef CONFIG_HIGHMEM
-
-#ifndef __GFP_RECLAIM
-#define	__GFP_RECLAIM		__GFP_WAIT
-#endif
-
-/*
- * The goal is to minimize fragmentation by preferentially populating ABDs
- * with higher order compound pages from a single zone.  Allocation size is
- * progressively decreased until it can be satisfied without performing
- * reclaim or compaction.  When necessary this function will degenerate to
- * allocating individual pages and allowing reclaim to satisfy allocations.
- */
-static void
-abd_alloc_pages(abd_t *abd, size_t size)
-{
-	struct list_head pages;
-	struct sg_table table;
-	struct scatterlist *sg;
-	struct page *page, *tmp_page = NULL;
-	gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
-	gfp_t gfp_comp = (gfp | __GFP_NORETRY | __GFP_COMP) & ~__GFP_RECLAIM;
-	int max_order = MIN(zfs_abd_scatter_max_order, MAX_ORDER - 1);
-	int nr_pages = abd_chunkcnt_for_bytes(size);
-	int chunks = 0, zones = 0;
-	size_t remaining_size;
-	int nid = NUMA_NO_NODE;
-	int alloc_pages = 0;
-
-	INIT_LIST_HEAD(&pages);
-
-	while (alloc_pages < nr_pages) {
-		unsigned chunk_pages;
-		int order;
-
-		order = MIN(highbit64(nr_pages - alloc_pages) - 1, max_order);
-		chunk_pages = (1U << order);
-
-		page = alloc_pages_node(nid, order ? gfp_comp : gfp, order);
-		if (page == NULL) {
-			if (order == 0) {
-				ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
-				schedule_timeout_interruptible(1);
-			} else {
-				max_order = MAX(0, order - 1);
-			}
-			continue;
-		}
-
-		list_add_tail(&page->lru, &pages);
-
-		if ((nid != NUMA_NO_NODE) && (page_to_nid(page) != nid))
-			zones++;
-
-		nid = page_to_nid(page);
-		ABDSTAT_BUMP(abdstat_scatter_orders[order]);
-		chunks++;
-		alloc_pages += chunk_pages;
-	}
-
-	ASSERT3S(alloc_pages, ==, nr_pages);
-
-	while (sg_alloc_table(&table, chunks, gfp)) {
-		ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
-		schedule_timeout_interruptible(1);
-	}
-
-	sg = table.sgl;
-	remaining_size = size;
-	list_for_each_entry_safe(page, tmp_page, &pages, lru) {
-		size_t sg_size = MIN(PAGESIZE << compound_order(page),
-		    remaining_size);
-		sg_set_page(sg, page, sg_size, 0);
-		abd_mark_zfs_page(page);
-		remaining_size -= sg_size;
-
-		sg = sg_next(sg);
-		list_del(&page->lru);
-	}
-
-	/*
-	 * These conditions ensure that a possible transformation to a linear
-	 * ABD would be valid.
-	 */
-	ASSERT(!PageHighMem(sg_page(table.sgl)));
-	ASSERT0(ABD_SCATTER(abd).abd_offset);
-
-	if (table.nents == 1) {
-		/*
-		 * Since there is only one entry, this ABD can be represented
-		 * as a linear buffer.  All single-page (4K) ABD's can be
-		 * represented this way.  Some multi-page ABD's can also be
-		 * represented this way, if we were able to allocate a single
-		 * "chunk" (higher-order "page" which represents a power-of-2
-		 * series of physically-contiguous pages).  This is often the
-		 * case for 2-page (8K) ABD's.
-		 *
-		 * Representing a single-entry scatter ABD as a linear ABD
-		 * has the performance advantage of avoiding the copy (and
-		 * allocation) in abd_borrow_buf_copy / abd_return_buf_copy.
-		 * A performance increase of around 5% has been observed for
-		 * ARC-cached reads (of small blocks which can take advantage
-		 * of this).
-		 *
-		 * Note that this optimization is only possible because the
-		 * pages are always mapped into the kernel's address space.
-		 * This is not the case for highmem pages, so the
-		 * optimization can not be made there.
-		 */
-		abd->abd_flags |= ABD_FLAG_LINEAR;
-		abd->abd_flags |= ABD_FLAG_LINEAR_PAGE;
-		abd->abd_u.abd_linear.abd_sgl = table.sgl;
-		abd->abd_u.abd_linear.abd_buf =
-		    page_address(sg_page(table.sgl));
-	} else if (table.nents > 1) {
-		ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
-		abd->abd_flags |= ABD_FLAG_MULTI_CHUNK;
-
-		if (zones) {
-			ABDSTAT_BUMP(abdstat_scatter_page_multi_zone);
-			abd->abd_flags |= ABD_FLAG_MULTI_ZONE;
-		}
-
-		ABD_SCATTER(abd).abd_sgl = table.sgl;
-		ABD_SCATTER(abd).abd_nents = table.nents;
-	}
-}
-#else
-/*
- * Allocate N individual pages to construct a scatter ABD.  This function
- * makes no attempt to request contiguous pages and requires the minimal
- * number of kernel interfaces.  It's designed for maximum compatibility.
- */
-static void
-abd_alloc_pages(abd_t *abd, size_t size)
-{
-	struct scatterlist *sg = NULL;
-	struct sg_table table;
-	struct page *page;
-	gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
-	int nr_pages = abd_chunkcnt_for_bytes(size);
-	int i = 0;
-
-	while (sg_alloc_table(&table, nr_pages, gfp)) {
-		ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
-		schedule_timeout_interruptible(1);
-	}
-
-	ASSERT3U(table.nents, ==, nr_pages);
-	ABD_SCATTER(abd).abd_sgl = table.sgl;
-	ABD_SCATTER(abd).abd_nents = nr_pages;
-
-	abd_for_each_sg(abd, sg, nr_pages, i) {
-		while ((page = __page_cache_alloc(gfp)) == NULL) {
-			ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
-			schedule_timeout_interruptible(1);
-		}
-
-		ABDSTAT_BUMP(abdstat_scatter_orders[0]);
-		sg_set_page(sg, page, PAGESIZE, 0);
-		abd_mark_zfs_page(page);
-	}
-
-	if (nr_pages > 1) {
-		ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
-		abd->abd_flags |= ABD_FLAG_MULTI_CHUNK;
-	}
-}
-#endif /* !CONFIG_HIGHMEM */
-
-static void
-abd_free_pages(abd_t *abd)
-{
-	struct scatterlist *sg = NULL;
-	struct sg_table table;
-	struct page *page;
-	int nr_pages = ABD_SCATTER(abd).abd_nents;
-	int order, i = 0;
-
-	if (abd->abd_flags & ABD_FLAG_MULTI_ZONE)
-		ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_zone);
-
-	if (abd->abd_flags & ABD_FLAG_MULTI_CHUNK)
-		ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_chunk);
-
-	abd_for_each_sg(abd, sg, nr_pages, i) {
-		page = sg_page(sg);
-		abd_unmark_zfs_page(page);
-		order = compound_order(page);
-		__free_pages(page, order);
-		ASSERT3U(sg->length, <=, PAGE_SIZE << order);
-		ABDSTAT_BUMPDOWN(abdstat_scatter_orders[order]);
-	}
-
-	table.sgl = ABD_SCATTER(abd).abd_sgl;
-	table.nents = table.orig_nents = nr_pages;
-	sg_free_table(&table);
-}
-
-#else /* _KERNEL */
-
-#ifndef PAGE_SHIFT
-#define	PAGE_SHIFT (highbit64(PAGESIZE)-1)
-#endif
-
-struct page;
-
-#define	zfs_kmap_atomic(chunk, km)	((void *)chunk)
-#define	zfs_kunmap_atomic(addr, km)	do { (void)(addr); } while (0)
-#define	local_irq_save(flags)		do { (void)(flags); } while (0)
-#define	local_irq_restore(flags)	do { (void)(flags); } while (0)
-#define	nth_page(pg, i) \
-	((struct page *)((void *)(pg) + (i) * PAGESIZE))
-
-struct scatterlist {
-	struct page *page;
-	int length;
-	int end;
-};
-
-static void
-sg_init_table(struct scatterlist *sg, int nr)
-{
-	memset(sg, 0, nr * sizeof (struct scatterlist));
-	sg[nr - 1].end = 1;
-}
-
-#define	for_each_sg(sgl, sg, nr, i)	\
-	for ((i) = 0, (sg) = (sgl); (i) < (nr); (i)++, (sg) = sg_next(sg))
-
-static inline void
-sg_set_page(struct scatterlist *sg, struct page *page, unsigned int len,
-    unsigned int offset)
-{
-	/* currently we don't use offset */
-	ASSERT(offset == 0);
-	sg->page = page;
-	sg->length = len;
-}
-
-static inline struct page *
-sg_page(struct scatterlist *sg)
-{
-	return (sg->page);
-}
-
-static inline struct scatterlist *
-sg_next(struct scatterlist *sg)
-{
-	if (sg->end)
-		return (NULL);
-
-	return (sg + 1);
-}
-
-static void
-abd_alloc_pages(abd_t *abd, size_t size)
-{
-	unsigned nr_pages = abd_chunkcnt_for_bytes(size);
-	struct scatterlist *sg;
-	int i;
-
-	ABD_SCATTER(abd).abd_sgl = vmem_alloc(nr_pages *
-	    sizeof (struct scatterlist), KM_SLEEP);
-	sg_init_table(ABD_SCATTER(abd).abd_sgl, nr_pages);
-
-	abd_for_each_sg(abd, sg, nr_pages, i) {
-		struct page *p = umem_alloc_aligned(PAGESIZE, 64, KM_SLEEP);
-		sg_set_page(sg, p, PAGESIZE, 0);
-	}
-	ABD_SCATTER(abd).abd_nents = nr_pages;
-}
-
-static void
-abd_free_pages(abd_t *abd)
-{
-	int i, n = ABD_SCATTER(abd).abd_nents;
-	struct scatterlist *sg;
-
-	abd_for_each_sg(abd, sg, n, i) {
-		for (int j = 0; j < sg->length; j += PAGESIZE) {
-			struct page *p = nth_page(sg_page(sg), j >> PAGE_SHIFT);
-			umem_free(p, PAGESIZE);
-		}
-	}
-
-	vmem_free(ABD_SCATTER(abd).abd_sgl, n * sizeof (struct scatterlist));
-}
-
-#endif /* _KERNEL */
-
-void
-abd_init(void)
-{
-	int i;
-
-	abd_cache = kmem_cache_create("abd_t", sizeof (abd_t),
-	    0, NULL, NULL, NULL, NULL, NULL, 0);
-
-	abd_ksp = kstat_create("zfs", 0, "abdstats", "misc", KSTAT_TYPE_NAMED,
-	    sizeof (abd_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
-	if (abd_ksp != NULL) {
-		for (i = 0; i < MAX_ORDER; i++) {
-			snprintf(abd_stats.abdstat_scatter_orders[i].name,
-			    KSTAT_STRLEN, "scatter_order_%d", i);
-			abd_stats.abdstat_scatter_orders[i].data_type =
-			    KSTAT_DATA_UINT64;
-		}
-		abd_ksp->ks_data = &abd_stats;
-		kstat_install(abd_ksp);
-	}
-}
-
-void
-abd_fini(void)
-{
-	if (abd_ksp != NULL) {
-		kstat_delete(abd_ksp);
-		abd_ksp = NULL;
-	}
-
-	if (abd_cache) {
-		kmem_cache_destroy(abd_cache);
-		abd_cache = NULL;
-	}
-}
-
-static inline void
-abd_verify(abd_t *abd)
-{
-	ASSERT3U(abd->abd_size, >, 0);
-	ASSERT3U(abd->abd_size, <=, SPA_MAXBLOCKSIZE);
-	ASSERT3U(abd->abd_flags, ==, abd->abd_flags & (ABD_FLAG_LINEAR |
-	    ABD_FLAG_OWNER | ABD_FLAG_META | ABD_FLAG_MULTI_ZONE |
-	    ABD_FLAG_MULTI_CHUNK | ABD_FLAG_LINEAR_PAGE));
-	IMPLY(abd->abd_parent != NULL, !(abd->abd_flags & ABD_FLAG_OWNER));
-	IMPLY(abd->abd_flags & ABD_FLAG_META, abd->abd_flags & ABD_FLAG_OWNER);
-	if (abd_is_linear(abd)) {
-		ASSERT3P(abd->abd_u.abd_linear.abd_buf, !=, NULL);
-	} else {
-		size_t n;
-		int i = 0;
-		struct scatterlist *sg = NULL;
-
-		ASSERT3U(ABD_SCATTER(abd).abd_nents, >, 0);
-		ASSERT3U(ABD_SCATTER(abd).abd_offset, <,
-		    ABD_SCATTER(abd).abd_sgl->length);
-		n = ABD_SCATTER(abd).abd_nents;
-		abd_for_each_sg(abd, sg, n, i) {
-			ASSERT3P(sg_page(sg), !=, NULL);
-		}
-	}
-}
-
-static inline abd_t *
-abd_alloc_struct(void)
-{
-	abd_t *abd = kmem_cache_alloc(abd_cache, KM_PUSHPAGE);
-
-	ASSERT3P(abd, !=, NULL);
-	ABDSTAT_INCR(abdstat_struct_size, sizeof (abd_t));
-
-	return (abd);
-}
-
-static inline void
-abd_free_struct(abd_t *abd)
-{
-	kmem_cache_free(abd_cache, abd);
-	ABDSTAT_INCR(abdstat_struct_size, -(int)sizeof (abd_t));
-}
-
-/*
- * Allocate an ABD, along with its own underlying data buffers. Use this if you
- * don't care whether the ABD is linear or not.
- */
-abd_t *
-abd_alloc(size_t size, boolean_t is_metadata)
-{
-	/* see the comment above zfs_abd_scatter_min_size */
-	if (!zfs_abd_scatter_enabled || size < zfs_abd_scatter_min_size)
-		return (abd_alloc_linear(size, is_metadata));
-
-	VERIFY3U(size, <=, SPA_MAXBLOCKSIZE);
-
-	abd_t *abd = abd_alloc_struct();
-	abd->abd_flags = ABD_FLAG_OWNER;
-	abd->abd_u.abd_scatter.abd_offset = 0;
-	abd_alloc_pages(abd, size);
-
-	if (is_metadata) {
-		abd->abd_flags |= ABD_FLAG_META;
-	}
-	abd->abd_size = size;
-	abd->abd_parent = NULL;
-	zfs_refcount_create(&abd->abd_children);
-
-	ABDSTAT_BUMP(abdstat_scatter_cnt);
-	ABDSTAT_INCR(abdstat_scatter_data_size, size);
-	ABDSTAT_INCR(abdstat_scatter_chunk_waste,
-	    P2ROUNDUP(size, PAGESIZE) - size);
-
-	return (abd);
-}
-
-static void
-abd_free_scatter(abd_t *abd)
-{
-	abd_free_pages(abd);
-
-	zfs_refcount_destroy(&abd->abd_children);
-	ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
-	ABDSTAT_INCR(abdstat_scatter_data_size, -(int)abd->abd_size);
-	ABDSTAT_INCR(abdstat_scatter_chunk_waste,
-	    (int)abd->abd_size - (int)P2ROUNDUP(abd->abd_size, PAGESIZE));
-
-	abd_free_struct(abd);
-}
-
-/*
- * Allocate an ABD that must be linear, along with its own underlying data
- * buffer. Only use this when it would be very annoying to write your ABD
- * consumer with a scattered ABD.
- */
-abd_t *
-abd_alloc_linear(size_t size, boolean_t is_metadata)
-{
-	abd_t *abd = abd_alloc_struct();
-
-	VERIFY3U(size, <=, SPA_MAXBLOCKSIZE);
-
-	abd->abd_flags = ABD_FLAG_LINEAR | ABD_FLAG_OWNER;
-	if (is_metadata) {
-		abd->abd_flags |= ABD_FLAG_META;
-	}
-	abd->abd_size = size;
-	abd->abd_parent = NULL;
-	zfs_refcount_create(&abd->abd_children);
-
-	if (is_metadata) {
-		abd->abd_u.abd_linear.abd_buf = zio_buf_alloc(size);
-	} else {
-		abd->abd_u.abd_linear.abd_buf = zio_data_buf_alloc(size);
-	}
-
-	ABDSTAT_BUMP(abdstat_linear_cnt);
-	ABDSTAT_INCR(abdstat_linear_data_size, size);
-
-	return (abd);
-}
-
-static void
-abd_free_linear(abd_t *abd)
-{
-	if (abd_is_linear_page(abd)) {
-		/* Transform it back into a scatter ABD for freeing */
-		struct scatterlist *sg = abd->abd_u.abd_linear.abd_sgl;
-		abd->abd_flags &= ~ABD_FLAG_LINEAR;
-		abd->abd_flags &= ~ABD_FLAG_LINEAR_PAGE;
-		ABD_SCATTER(abd).abd_nents = 1;
-		ABD_SCATTER(abd).abd_offset = 0;
-		ABD_SCATTER(abd).abd_sgl = sg;
-		abd_free_scatter(abd);
-		return;
-	}
-	if (abd->abd_flags & ABD_FLAG_META) {
-		zio_buf_free(abd->abd_u.abd_linear.abd_buf, abd->abd_size);
-	} else {
-		zio_data_buf_free(abd->abd_u.abd_linear.abd_buf, abd->abd_size);
-	}
-
-	zfs_refcount_destroy(&abd->abd_children);
-	ABDSTAT_BUMPDOWN(abdstat_linear_cnt);
-	ABDSTAT_INCR(abdstat_linear_data_size, -(int)abd->abd_size);
-
-	abd_free_struct(abd);
-}
-
-/*
- * Free an ABD. Only use this on ABDs allocated with abd_alloc() or
- * abd_alloc_linear().
- */
-void
-abd_free(abd_t *abd)
-{
-	abd_verify(abd);
-	ASSERT3P(abd->abd_parent, ==, NULL);
-	ASSERT(abd->abd_flags & ABD_FLAG_OWNER);
-	if (abd_is_linear(abd))
-		abd_free_linear(abd);
-	else
-		abd_free_scatter(abd);
-}
-
-/*
- * Allocate an ABD of the same format (same metadata flag, same scatterize
- * setting) as another ABD.
- */
-abd_t *
-abd_alloc_sametype(abd_t *sabd, size_t size)
-{
-	boolean_t is_metadata = (sabd->abd_flags & ABD_FLAG_META) != 0;
-	if (abd_is_linear(sabd) &&
-	    !abd_is_linear_page(sabd)) {
-		return (abd_alloc_linear(size, is_metadata));
-	} else {
-		return (abd_alloc(size, is_metadata));
-	}
-}
-
-/*
- * If we're going to use this ABD for doing I/O using the block layer, the
- * consumer of the ABD data doesn't care if it's scattered or not, and we don't
- * plan to store this ABD in memory for a long period of time, we should
- * allocate the ABD type that requires the least data copying to do the I/O.
- *
- * On Illumos this is linear ABDs, however if ldi_strategy() can ever issue I/Os
- * using a scatter/gather list we should switch to that and replace this call
- * with vanilla abd_alloc().
- *
- * On Linux the optimal thing to do would be to use abd_get_offset() and
- * construct a new ABD which shares the original pages thereby eliminating
- * the copy.  But for the moment a new linear ABD is allocated until this
- * performance optimization can be implemented.
- */
-abd_t *
-abd_alloc_for_io(size_t size, boolean_t is_metadata)
-{
-	return (abd_alloc(size, is_metadata));
-}
-
-/*
- * Allocate a new ABD to point to offset off of sabd. It shares the underlying
- * buffer data with sabd. Use abd_put() to free. sabd must not be freed while
- * any derived ABDs exist.
- */
-static inline abd_t *
-abd_get_offset_impl(abd_t *sabd, size_t off, size_t size)
-{
-	abd_t *abd;
-
-	abd_verify(sabd);
-	ASSERT3U(off, <=, sabd->abd_size);
-
-	if (abd_is_linear(sabd)) {
-		abd = abd_alloc_struct();
-
-		/*
-		 * Even if this buf is filesystem metadata, we only track that
-		 * if we own the underlying data buffer, which is not true in
-		 * this case. Therefore, we don't ever use ABD_FLAG_META here.
-		 */
-		abd->abd_flags = ABD_FLAG_LINEAR;
-
-		abd->abd_u.abd_linear.abd_buf =
-		    (char *)sabd->abd_u.abd_linear.abd_buf + off;
-	} else {
-		int i = 0;
-		struct scatterlist *sg = NULL;
-		size_t new_offset = sabd->abd_u.abd_scatter.abd_offset + off;
-
-		abd = abd_alloc_struct();
-
-		/*
-		 * Even if this buf is filesystem metadata, we only track that
-		 * if we own the underlying data buffer, which is not true in
-		 * this case. Therefore, we don't ever use ABD_FLAG_META here.
-		 */
-		abd->abd_flags = 0;
-
-		abd_for_each_sg(sabd, sg, ABD_SCATTER(sabd).abd_nents, i) {
-			if (new_offset < sg->length)
-				break;
-			new_offset -= sg->length;
-		}
-
-		ABD_SCATTER(abd).abd_sgl = sg;
-		ABD_SCATTER(abd).abd_offset = new_offset;
-		ABD_SCATTER(abd).abd_nents = ABD_SCATTER(sabd).abd_nents - i;
-	}
-
-	abd->abd_size = size;
-	abd->abd_parent = sabd;
-	zfs_refcount_create(&abd->abd_children);
-	(void) zfs_refcount_add_many(&sabd->abd_children, abd->abd_size, abd);
-
-	return (abd);
-}
-
-abd_t *
-abd_get_offset(abd_t *sabd, size_t off)
-{
-	size_t size = sabd->abd_size > off ? sabd->abd_size - off : 0;
-
-	VERIFY3U(size, >, 0);
-
-	return (abd_get_offset_impl(sabd, off, size));
-}
-
-abd_t *
-abd_get_offset_size(abd_t *sabd, size_t off, size_t size)
-{
-	ASSERT3U(off + size, <=, sabd->abd_size);
-
-	return (abd_get_offset_impl(sabd, off, size));
-}
-
-/*
- * Allocate a linear ABD structure for buf. You must free this with abd_put()
- * since the resulting ABD doesn't own its own buffer.
- */
-abd_t *
-abd_get_from_buf(void *buf, size_t size)
-{
-	abd_t *abd = abd_alloc_struct();
-
-	VERIFY3U(size, <=, SPA_MAXBLOCKSIZE);
-
-	/*
-	 * Even if this buf is filesystem metadata, we only track that if we
-	 * own the underlying data buffer, which is not true in this case.
-	 * Therefore, we don't ever use ABD_FLAG_META here.
-	 */
-	abd->abd_flags = ABD_FLAG_LINEAR;
-	abd->abd_size = size;
-	abd->abd_parent = NULL;
-	zfs_refcount_create(&abd->abd_children);
-
-	abd->abd_u.abd_linear.abd_buf = buf;
-
-	return (abd);
-}
-
-/*
- * Free an ABD allocated from abd_get_offset() or abd_get_from_buf(). Will not
- * free the underlying scatterlist or buffer.
- */
-void
-abd_put(abd_t *abd)
-{
-	abd_verify(abd);
-	ASSERT(!(abd->abd_flags & ABD_FLAG_OWNER));
-
-	if (abd->abd_parent != NULL) {
-		(void) zfs_refcount_remove_many(&abd->abd_parent->abd_children,
-		    abd->abd_size, abd);
-	}
-
-	zfs_refcount_destroy(&abd->abd_children);
-	abd_free_struct(abd);
-}
-
-/*
- * Get the raw buffer associated with a linear ABD.
- */
-void *
-abd_to_buf(abd_t *abd)
-{
-	ASSERT(abd_is_linear(abd));
-	abd_verify(abd);
-	return (abd->abd_u.abd_linear.abd_buf);
-}
-
-/*
- * Borrow a raw buffer from an ABD without copying the contents of the ABD
- * into the buffer. If the ABD is scattered, this will allocate a raw buffer
- * whose contents are undefined. To copy over the existing data in the ABD, use
- * abd_borrow_buf_copy() instead.
- */
-void *
-abd_borrow_buf(abd_t *abd, size_t n)
-{
-	void *buf;
-	abd_verify(abd);
-	ASSERT3U(abd->abd_size, >=, n);
-	if (abd_is_linear(abd)) {
-		buf = abd_to_buf(abd);
-	} else {
-		buf = zio_buf_alloc(n);
-	}
-	(void) zfs_refcount_add_many(&abd->abd_children, n, buf);
-
-	return (buf);
-}
-
-void *
-abd_borrow_buf_copy(abd_t *abd, size_t n)
-{
-	void *buf = abd_borrow_buf(abd, n);
-	if (!abd_is_linear(abd)) {
-		abd_copy_to_buf(buf, abd, n);
-	}
-	return (buf);
-}
-
-/*
- * Return a borrowed raw buffer to an ABD. If the ABD is scattered, this will
- * not change the contents of the ABD and will ASSERT that you didn't modify
- * the buffer since it was borrowed. If you want any changes you made to buf to
- * be copied back to abd, use abd_return_buf_copy() instead.
- */
-void
-abd_return_buf(abd_t *abd, void *buf, size_t n)
-{
-	abd_verify(abd);
-	ASSERT3U(abd->abd_size, >=, n);
-	if (abd_is_linear(abd)) {
-		ASSERT3P(buf, ==, abd_to_buf(abd));
-	} else {
-		ASSERT0(abd_cmp_buf(abd, buf, n));
-		zio_buf_free(buf, n);
-	}
-	(void) zfs_refcount_remove_many(&abd->abd_children, n, buf);
-}
-
-void
-abd_return_buf_copy(abd_t *abd, void *buf, size_t n)
-{
-	if (!abd_is_linear(abd)) {
-		abd_copy_from_buf(abd, buf, n);
-	}
-	abd_return_buf(abd, buf, n);
-}
-
-/*
- * Give this ABD ownership of the buffer that it's storing. Can only be used on
- * linear ABDs which were allocated via abd_get_from_buf(), or ones allocated
- * with abd_alloc_linear() which subsequently released ownership of their buf
- * with abd_release_ownership_of_buf().
- */
-void
-abd_take_ownership_of_buf(abd_t *abd, boolean_t is_metadata)
-{
-	ASSERT(abd_is_linear(abd));
-	ASSERT(!(abd->abd_flags & ABD_FLAG_OWNER));
-	abd_verify(abd);
-
-	abd->abd_flags |= ABD_FLAG_OWNER;
-	if (is_metadata) {
-		abd->abd_flags |= ABD_FLAG_META;
-	}
-
-	ABDSTAT_BUMP(abdstat_linear_cnt);
-	ABDSTAT_INCR(abdstat_linear_data_size, abd->abd_size);
-}
-
-void
-abd_release_ownership_of_buf(abd_t *abd)
-{
-	ASSERT(abd_is_linear(abd));
-	ASSERT(abd->abd_flags & ABD_FLAG_OWNER);
-
-	/*
-	 * abd_free() needs to handle LINEAR_PAGE ABD's specially.
-	 * Since that flag does not survive the
-	 * abd_release_ownership_of_buf() -> abd_get_from_buf() ->
-	 * abd_take_ownership_of_buf() sequence, we don't allow releasing
-	 * these "linear but not zio_[data_]buf_alloc()'ed" ABD's.
-	 */
-	ASSERT(!abd_is_linear_page(abd));
-
-	abd_verify(abd);
-
-	abd->abd_flags &= ~ABD_FLAG_OWNER;
-	/* Disable this flag since we no longer own the data buffer */
-	abd->abd_flags &= ~ABD_FLAG_META;
-
-	ABDSTAT_BUMPDOWN(abdstat_linear_cnt);
-	ABDSTAT_INCR(abdstat_linear_data_size, -(int)abd->abd_size);
-}
-
-struct abd_iter {
-	/* public interface */
-	void		*iter_mapaddr;	/* addr corresponding to iter_pos */
-	size_t		iter_mapsize;	/* length of data valid at mapaddr */
-
-	/* private */
-	abd_t		*iter_abd;	/* ABD being iterated through */
-	size_t		iter_pos;
-	size_t		iter_offset;	/* offset in current sg/abd_buf, */
-					/* abd_offset included */
-	struct scatterlist *iter_sg;	/* current sg */
-};
-
-/*
- * Initialize the abd_iter.
- */
-static void
-abd_iter_init(struct abd_iter *aiter, abd_t *abd, int km_type)
-{
-	abd_verify(abd);
-	aiter->iter_abd = abd;
-	aiter->iter_mapaddr = NULL;
-	aiter->iter_mapsize = 0;
-	aiter->iter_pos = 0;
-	if (abd_is_linear(abd)) {
-		aiter->iter_offset = 0;
-		aiter->iter_sg = NULL;
-	} else {
-		aiter->iter_offset = ABD_SCATTER(abd).abd_offset;
-		aiter->iter_sg = ABD_SCATTER(abd).abd_sgl;
-	}
-}
-
-/*
- * Advance the iterator by a certain amount. Cannot be called when a chunk is
- * in use. This can be safely called when the aiter has already exhausted, in
- * which case this does nothing.
- */
-static void
-abd_iter_advance(struct abd_iter *aiter, size_t amount)
-{
-	ASSERT3P(aiter->iter_mapaddr, ==, NULL);
-	ASSERT0(aiter->iter_mapsize);
-
-	/* There's nothing left to advance to, so do nothing */
-	if (aiter->iter_pos == aiter->iter_abd->abd_size)
-		return;
-
-	aiter->iter_pos += amount;
-	aiter->iter_offset += amount;
-	if (!abd_is_linear(aiter->iter_abd)) {
-		while (aiter->iter_offset >= aiter->iter_sg->length) {
-			aiter->iter_offset -= aiter->iter_sg->length;
-			aiter->iter_sg = sg_next(aiter->iter_sg);
-			if (aiter->iter_sg == NULL) {
-				ASSERT0(aiter->iter_offset);
-				break;
-			}
-		}
-	}
-}
-
-/*
- * Map the current chunk into aiter. This can be safely called when the aiter
- * has already exhausted, in which case this does nothing.
- */
-static void
-abd_iter_map(struct abd_iter *aiter)
-{
-	void *paddr;
-	size_t offset = 0;
-
-	ASSERT3P(aiter->iter_mapaddr, ==, NULL);
-	ASSERT0(aiter->iter_mapsize);
-
-	/* There's nothing left to iterate over, so do nothing */
-	if (aiter->iter_pos == aiter->iter_abd->abd_size)
-		return;
-
-	if (abd_is_linear(aiter->iter_abd)) {
-		ASSERT3U(aiter->iter_pos, ==, aiter->iter_offset);
-		offset = aiter->iter_offset;
-		aiter->iter_mapsize = aiter->iter_abd->abd_size - offset;
-		paddr = aiter->iter_abd->abd_u.abd_linear.abd_buf;
-	} else {
-		offset = aiter->iter_offset;
-		aiter->iter_mapsize = MIN(aiter->iter_sg->length - offset,
-		    aiter->iter_abd->abd_size - aiter->iter_pos);
-
-		paddr = zfs_kmap_atomic(sg_page(aiter->iter_sg),
-		    km_table[aiter->iter_km]);
-	}
-
-	aiter->iter_mapaddr = (char *)paddr + offset;
-}
-
-/*
- * Unmap the current chunk from aiter. This can be safely called when the aiter
- * has already exhausted, in which case this does nothing.
- */
-static void
-abd_iter_unmap(struct abd_iter *aiter)
-{
-	/* There's nothing left to unmap, so do nothing */
-	if (aiter->iter_pos == aiter->iter_abd->abd_size)
-		return;
-
-	if (!abd_is_linear(aiter->iter_abd)) {
-		/* LINTED E_FUNC_SET_NOT_USED */
-		zfs_kunmap_atomic(aiter->iter_mapaddr - aiter->iter_offset,
-		    km_table[aiter->iter_km]);
-	}
-
-	ASSERT3P(aiter->iter_mapaddr, !=, NULL);
-	ASSERT3U(aiter->iter_mapsize, >, 0);
-
-	aiter->iter_mapaddr = NULL;
-	aiter->iter_mapsize = 0;
-}
-
-int
-abd_iterate_func(abd_t *abd, size_t off, size_t size,
-    abd_iter_func_t *func, void *private)
-{
-	int ret = 0;
-	struct abd_iter aiter;
-
-	abd_verify(abd);
-	ASSERT3U(off + size, <=, abd->abd_size);
-
-	abd_iter_init(&aiter, abd, 0);
-	abd_iter_advance(&aiter, off);
-
-	while (size > 0) {
-		abd_iter_map(&aiter);
-
-		size_t len = MIN(aiter.iter_mapsize, size);
-		ASSERT3U(len, >, 0);
-
-		ret = func(aiter.iter_mapaddr, len, private);
-
-		abd_iter_unmap(&aiter);
-
-		if (ret != 0)
-			break;
-
-		size -= len;
-		abd_iter_advance(&aiter, len);
-	}
-
-	return (ret);
-}
-
-struct buf_arg {
-	void *arg_buf;
-};
-
-static int
-abd_copy_to_buf_off_cb(void *buf, size_t size, void *private)
-{
-	struct buf_arg *ba_ptr = private;
-
-	(void) memcpy(ba_ptr->arg_buf, buf, size);
-	ba_ptr->arg_buf = (char *)ba_ptr->arg_buf + size;
-
-	return (0);
-}
-
-/*
- * Copy abd to buf. (off is the offset in abd.)
- */
-void
-abd_copy_to_buf_off(void *buf, abd_t *abd, size_t off, size_t size)
-{
-	struct buf_arg ba_ptr = { buf };
-
-	(void) abd_iterate_func(abd, off, size, abd_copy_to_buf_off_cb,
-	    &ba_ptr);
-}
-
-static int
-abd_cmp_buf_off_cb(void *buf, size_t size, void *private)
-{
-	int ret;
-	struct buf_arg *ba_ptr = private;
-
-	ret = memcmp(buf, ba_ptr->arg_buf, size);
-	ba_ptr->arg_buf = (char *)ba_ptr->arg_buf + size;
-
-	return (ret);
-}
-
-/*
- * Compare the contents of abd to buf. (off is the offset in abd.)
- */
-int
-abd_cmp_buf_off(abd_t *abd, const void *buf, size_t off, size_t size)
-{
-	struct buf_arg ba_ptr = { (void *) buf };
-
-	return (abd_iterate_func(abd, off, size, abd_cmp_buf_off_cb, &ba_ptr));
-}
-
-static int
-abd_copy_from_buf_off_cb(void *buf, size_t size, void *private)
-{
-	struct buf_arg *ba_ptr = private;
-
-	(void) memcpy(buf, ba_ptr->arg_buf, size);
-	ba_ptr->arg_buf = (char *)ba_ptr->arg_buf + size;
-
-	return (0);
-}
-
-/*
- * Copy from buf to abd. (off is the offset in abd.)
- */
-void
-abd_copy_from_buf_off(abd_t *abd, const void *buf, size_t off, size_t size)
-{
-	struct buf_arg ba_ptr = { (void *) buf };
-
-	(void) abd_iterate_func(abd, off, size, abd_copy_from_buf_off_cb,
-	    &ba_ptr);
-}
-
-/*ARGSUSED*/
-static int
-abd_zero_off_cb(void *buf, size_t size, void *private)
-{
-	(void) memset(buf, 0, size);
-	return (0);
-}
-
-/*
- * Zero out the abd from a particular offset to the end.
- */
-void
-abd_zero_off(abd_t *abd, size_t off, size_t size)
-{
-	(void) abd_iterate_func(abd, off, size, abd_zero_off_cb, NULL);
-}
-
-/*
- * Iterate over two ABDs and call func incrementally on the two ABDs' data in
- * equal-sized chunks (passed to func as raw buffers). func could be called many
- * times during this iteration.
- */
-int
-abd_iterate_func2(abd_t *dabd, abd_t *sabd, size_t doff, size_t soff,
-    size_t size, abd_iter_func2_t *func, void *private)
-{
-	int ret = 0;
-	struct abd_iter daiter, saiter;
-
-	abd_verify(dabd);
-	abd_verify(sabd);
-
-	ASSERT3U(doff + size, <=, dabd->abd_size);
-	ASSERT3U(soff + size, <=, sabd->abd_size);
-
-	abd_iter_init(&daiter, dabd, 0);
-	abd_iter_init(&saiter, sabd, 1);
-	abd_iter_advance(&daiter, doff);
-	abd_iter_advance(&saiter, soff);
-
-	while (size > 0) {
-		abd_iter_map(&daiter);
-		abd_iter_map(&saiter);
-
-		size_t dlen = MIN(daiter.iter_mapsize, size);
-		size_t slen = MIN(saiter.iter_mapsize, size);
-		size_t len = MIN(dlen, slen);
-		ASSERT(dlen > 0 || slen > 0);
-
-		ret = func(daiter.iter_mapaddr, saiter.iter_mapaddr, len,
-		    private);
-
-		abd_iter_unmap(&saiter);
-		abd_iter_unmap(&daiter);
-
-		if (ret != 0)
-			break;
-
-		size -= len;
-		abd_iter_advance(&daiter, len);
-		abd_iter_advance(&saiter, len);
-	}
-
-	return (ret);
-}
-
-/*ARGSUSED*/
-static int
-abd_copy_off_cb(void *dbuf, void *sbuf, size_t size, void *private)
-{
-	(void) memcpy(dbuf, sbuf, size);
-	return (0);
-}
-
-/*
- * Copy from sabd to dabd starting from soff and doff.
- */
-void
-abd_copy_off(abd_t *dabd, abd_t *sabd, size_t doff, size_t soff, size_t size)
-{
-	(void) abd_iterate_func2(dabd, sabd, doff, soff, size,
-	    abd_copy_off_cb, NULL);
-}
-
-/*ARGSUSED*/
-static int
-abd_cmp_cb(void *bufa, void *bufb, size_t size, void *private)
-{
-	return (memcmp(bufa, bufb, size));
-}
-
-/*
- * Compares the contents of two ABDs.
- */
-int
-abd_cmp(abd_t *dabd, abd_t *sabd)
-{
-	ASSERT3U(dabd->abd_size, ==, sabd->abd_size);
-	return (abd_iterate_func2(dabd, sabd, 0, 0, dabd->abd_size,
-	    abd_cmp_cb, NULL));
-}
-
-/*
- * Iterate over code ABDs and a data ABD and call @func_raidz_gen.
- *
- * @cabds          parity ABDs, must have equal size
- * @dabd           data ABD. Can be NULL (in this case @dsize = 0)
- * @func_raidz_gen should be implemented so that its behaviour
- *                 is the same when taking linear and when taking scatter
- */
-void
-abd_raidz_gen_iterate(abd_t **cabds, abd_t *dabd,
-    ssize_t csize, ssize_t dsize, const unsigned parity,
-    void (*func_raidz_gen)(void **, const void *, size_t, size_t))
-{
-	int i;
-	ssize_t len, dlen;
-	struct abd_iter caiters[3];
-	struct abd_iter daiter = {0};
-	void *caddrs[3];
-	unsigned long flags;
-
-	ASSERT3U(parity, <=, 3);
-
-	for (i = 0; i < parity; i++)
-		abd_iter_init(&caiters[i], cabds[i], i);
-
-	if (dabd)
-		abd_iter_init(&daiter, dabd, i);
-
-	ASSERT3S(dsize, >=, 0);
-
-	local_irq_save(flags);
-	while (csize > 0) {
-		len = csize;
-
-		if (dabd && dsize > 0)
-			abd_iter_map(&daiter);
-
-		for (i = 0; i < parity; i++) {
-			abd_iter_map(&caiters[i]);
-			caddrs[i] = caiters[i].iter_mapaddr;
-		}
-
-		switch (parity) {
-			case 3:
-				len = MIN(caiters[2].iter_mapsize, len);
-				/* falls through */
-			case 2:
-				len = MIN(caiters[1].iter_mapsize, len);
-				/* falls through */
-			case 1:
-				len = MIN(caiters[0].iter_mapsize, len);
-		}
-
-		/* must be progressive */
-		ASSERT3S(len, >, 0);
-
-		if (dabd && dsize > 0) {
-			/* this needs precise iter.length */
-			len = MIN(daiter.iter_mapsize, len);
-			dlen = len;
-		} else
-			dlen = 0;
-
-		/* must be progressive */
-		ASSERT3S(len, >, 0);
-		/*
-		 * The iterated function likely will not do well if each
-		 * segment except the last one is not multiple of 512 (raidz).
-		 */
-		ASSERT3U(((uint64_t)len & 511ULL), ==, 0);
-
-		func_raidz_gen(caddrs, daiter.iter_mapaddr, len, dlen);
-
-		for (i = parity-1; i >= 0; i--) {
-			abd_iter_unmap(&caiters[i]);
-			abd_iter_advance(&caiters[i], len);
-		}
-
-		if (dabd && dsize > 0) {
-			abd_iter_unmap(&daiter);
-			abd_iter_advance(&daiter, dlen);
-			dsize -= dlen;
-		}
-
-		csize -= len;
-
-		ASSERT3S(dsize, >=, 0);
-		ASSERT3S(csize, >=, 0);
-	}
-	local_irq_restore(flags);
-}
-
-/*
- * Iterate over code ABDs and data reconstruction target ABDs and call
- * @func_raidz_rec. Function maps at most 6 pages atomically.
- *
- * @cabds           parity ABDs, must have equal size
- * @tabds           rec target ABDs, at most 3
- * @tsize           size of data target columns
- * @func_raidz_rec  expects syndrome data in target columns. Function
- *                  reconstructs data and overwrites target columns.
- */
-void
-abd_raidz_rec_iterate(abd_t **cabds, abd_t **tabds,
-    ssize_t tsize, const unsigned parity,
-    void (*func_raidz_rec)(void **t, const size_t tsize, void **c,
-    const unsigned *mul),
-    const unsigned *mul)
-{
-	int i;
-	ssize_t len;
-	struct abd_iter citers[3];
-	struct abd_iter xiters[3];
-	void *caddrs[3], *xaddrs[3];
-	unsigned long flags;
-
-	ASSERT3U(parity, <=, 3);
-
-	for (i = 0; i < parity; i++) {
-		abd_iter_init(&citers[i], cabds[i], 2*i);
-		abd_iter_init(&xiters[i], tabds[i], 2*i+1);
-	}
-
-	local_irq_save(flags);
-	while (tsize > 0) {
-
-		for (i = 0; i < parity; i++) {
-			abd_iter_map(&citers[i]);
-			abd_iter_map(&xiters[i]);
-			caddrs[i] = citers[i].iter_mapaddr;
-			xaddrs[i] = xiters[i].iter_mapaddr;
-		}
-
-		len = tsize;
-		switch (parity) {
-			case 3:
-				len = MIN(xiters[2].iter_mapsize, len);
-				len = MIN(citers[2].iter_mapsize, len);
-				/* falls through */
-			case 2:
-				len = MIN(xiters[1].iter_mapsize, len);
-				len = MIN(citers[1].iter_mapsize, len);
-				/* falls through */
-			case 1:
-				len = MIN(xiters[0].iter_mapsize, len);
-				len = MIN(citers[0].iter_mapsize, len);
-		}
-		/* must be progressive */
-		ASSERT3S(len, >, 0);
-		/*
-		 * The iterated function likely will not do well if each
-		 * segment except the last one is not multiple of 512 (raidz).
-		 */
-		ASSERT3U(((uint64_t)len & 511ULL), ==, 0);
-
-		func_raidz_rec(xaddrs, len, caddrs, mul);
-
-		for (i = parity-1; i >= 0; i--) {
-			abd_iter_unmap(&xiters[i]);
-			abd_iter_unmap(&citers[i]);
-			abd_iter_advance(&xiters[i], len);
-			abd_iter_advance(&citers[i], len);
-		}
-
-		tsize -= len;
-		ASSERT3S(tsize, >=, 0);
-	}
-	local_irq_restore(flags);
-}
-
-#if defined(_KERNEL)
-/*
- * bio_nr_pages for ABD.
- * @off is the offset in @abd
- */
-unsigned long
-abd_nr_pages_off(abd_t *abd, unsigned int size, size_t off)
-{
-	unsigned long pos;
-
-	if (abd_is_linear(abd))
-		pos = (unsigned long)abd_to_buf(abd) + off;
-	else
-		pos = abd->abd_u.abd_scatter.abd_offset + off;
-
-	return ((pos + size + PAGESIZE - 1) >> PAGE_SHIFT) -
-	    (pos >> PAGE_SHIFT);
-}
-
-/*
- * bio_map for scatter ABD.
- * @off is the offset in @abd
- * Remaining IO size is returned
- */
-unsigned int
-abd_scatter_bio_map_off(struct bio *bio, abd_t *abd,
-    unsigned int io_size, size_t off)
-{
-	int i;
-	struct abd_iter aiter;
-
-	ASSERT(!abd_is_linear(abd));
-	ASSERT3U(io_size, <=, abd->abd_size - off);
-
-	abd_iter_init(&aiter, abd, 0);
-	abd_iter_advance(&aiter, off);
-
-	for (i = 0; i < bio->bi_max_vecs; i++) {
-		struct page *pg;
-		size_t len, sgoff, pgoff;
-		struct scatterlist *sg;
-
-		if (io_size <= 0)
-			break;
-
-		sg = aiter.iter_sg;
-		sgoff = aiter.iter_offset;
-		pgoff = sgoff & (PAGESIZE - 1);
-		len = MIN(io_size, PAGESIZE - pgoff);
-		ASSERT(len > 0);
-
-		pg = nth_page(sg_page(sg), sgoff >> PAGE_SHIFT);
-		if (bio_add_page(bio, pg, len, pgoff) != len)
-			break;
-
-		io_size -= len;
-		abd_iter_advance(&aiter, len);
-	}
-
-	return (io_size);
-}
-
-/* Tunable Parameters */
-module_param(zfs_abd_scatter_enabled, int, 0644);
-MODULE_PARM_DESC(zfs_abd_scatter_enabled,
-	"Toggle whether ABD allocations must be linear.");
-module_param(zfs_abd_scatter_min_size, int, 0644);
-MODULE_PARM_DESC(zfs_abd_scatter_min_size,
-	"Minimum size of scatter allocations.");
-/* CSTYLED */
-module_param(zfs_abd_scatter_max_order, uint, 0644);
-MODULE_PARM_DESC(zfs_abd_scatter_max_order,
-	"Maximum order allocation used for a scatter ABD.");
-#endif