xref: /freebsd/sys/contrib/openzfs/module/os/linux/zfs/abd_os.c (revision 38a52bd3b5cac3da6f7f6eef3dd050e6aa08ebb3)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or https://opensource.org/licenses/CDDL-1.0.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright (c) 2014 by Chunwei Chen. All rights reserved.
23  * Copyright (c) 2019 by Delphix. All rights reserved.
24  */
25 
26 /*
27  * See abd.c for a general overview of the arc buffered data (ABD).
28  *
29  * Linear buffers act exactly like normal buffers and are always mapped into the
30  * kernel's virtual memory space, while scattered ABD data chunks are allocated
31  * as physical pages and then mapped in only while they are actually being
32  * accessed through one of the abd_* library functions. Using scattered ABDs
33  * provides several benefits:
34  *
35  *  (1) They avoid use of kmem_*, preventing performance problems where running
36  *      kmem_reap on very large memory systems never finishes and causes
37  *      constant TLB shootdowns.
38  *
39  *  (2) Fragmentation is less of an issue since when we are at the limit of
40  *      allocatable space, we won't have to search around for a long free
41  *      hole in the VA space for large ARC allocations. Each chunk is mapped in
42  *      individually, so even if we are using HIGHMEM (see next point) we
43  *      wouldn't need to worry about finding a contiguous address range.
44  *
45  *  (3) If we are not using HIGHMEM, then all physical memory is always
46  *      mapped into the kernel's address space, so we also avoid the map /
47  *      unmap costs on each ABD access.
48  *
49  * If we are not using HIGHMEM, scattered buffers which have only one chunk
50  * can be treated as linear buffers, because they are contiguous in the
51  * kernel's virtual address space.  See abd_alloc_chunks() for details.
52  */
53 
54 #include <sys/abd_impl.h>
55 #include <sys/param.h>
56 #include <sys/zio.h>
57 #include <sys/arc.h>
58 #include <sys/zfs_context.h>
59 #include <sys/zfs_znode.h>
60 #ifdef _KERNEL
61 #include <linux/kmap_compat.h>
62 #include <linux/scatterlist.h>
63 #else
64 #define	MAX_ORDER	1
65 #endif
66 
67 typedef struct abd_stats {
68 	kstat_named_t abdstat_struct_size;
69 	kstat_named_t abdstat_linear_cnt;
70 	kstat_named_t abdstat_linear_data_size;
71 	kstat_named_t abdstat_scatter_cnt;
72 	kstat_named_t abdstat_scatter_data_size;
73 	kstat_named_t abdstat_scatter_chunk_waste;
74 	kstat_named_t abdstat_scatter_orders[MAX_ORDER];
75 	kstat_named_t abdstat_scatter_page_multi_chunk;
76 	kstat_named_t abdstat_scatter_page_multi_zone;
77 	kstat_named_t abdstat_scatter_page_alloc_retry;
78 	kstat_named_t abdstat_scatter_sg_table_retry;
79 } abd_stats_t;
80 
81 static abd_stats_t abd_stats = {
82 	/* Amount of memory occupied by all of the abd_t struct allocations */
83 	{ "struct_size",			KSTAT_DATA_UINT64 },
84 	/*
85 	 * The number of linear ABDs which are currently allocated, excluding
86 	 * ABDs which don't own their data (for instance the ones which were
87 	 * allocated through abd_get_offset() and abd_get_from_buf()). If an
88 	 * ABD takes ownership of its buf then it will become tracked.
89 	 */
90 	{ "linear_cnt",				KSTAT_DATA_UINT64 },
91 	/* Amount of data stored in all linear ABDs tracked by linear_cnt */
92 	{ "linear_data_size",			KSTAT_DATA_UINT64 },
93 	/*
94 	 * The number of scatter ABDs which are currently allocated, excluding
95 	 * ABDs which don't own their data (for instance the ones which were
96 	 * allocated through abd_get_offset()).
97 	 */
98 	{ "scatter_cnt",			KSTAT_DATA_UINT64 },
99 	/* Amount of data stored in all scatter ABDs tracked by scatter_cnt */
100 	{ "scatter_data_size",			KSTAT_DATA_UINT64 },
101 	/*
102 	 * The amount of space wasted at the end of the last chunk across all
103 	 * scatter ABDs tracked by scatter_cnt.
104 	 */
105 	{ "scatter_chunk_waste",		KSTAT_DATA_UINT64 },
106 	/*
107 	 * The number of compound allocations of a given order.  These
108 	 * allocations are spread over all currently allocated ABDs, and
109 	 * act as a measure of memory fragmentation.
110 	 */
111 	{ { "scatter_order_N",			KSTAT_DATA_UINT64 } },
112 	/*
113 	 * The number of scatter ABDs which contain multiple chunks.
114 	 * ABDs are preferentially allocated from the minimum number of
115 	 * contiguous multi-page chunks, a single chunk is optimal.
116 	 */
117 	{ "scatter_page_multi_chunk",		KSTAT_DATA_UINT64 },
118 	/*
119 	 * The number of scatter ABDs which are split across memory zones.
120 	 * ABDs are preferentially allocated using pages from a single zone.
121 	 */
122 	{ "scatter_page_multi_zone",		KSTAT_DATA_UINT64 },
123 	/*
124 	 *  The total number of retries encountered when attempting to
125 	 *  allocate the pages to populate the scatter ABD.
126 	 */
127 	{ "scatter_page_alloc_retry",		KSTAT_DATA_UINT64 },
128 	/*
129 	 *  The total number of retries encountered when attempting to
130 	 *  allocate the sg table for an ABD.
131 	 */
132 	{ "scatter_sg_table_retry",		KSTAT_DATA_UINT64 },
133 };
134 
135 struct {
136 	wmsum_t abdstat_struct_size;
137 	wmsum_t abdstat_linear_cnt;
138 	wmsum_t abdstat_linear_data_size;
139 	wmsum_t abdstat_scatter_cnt;
140 	wmsum_t abdstat_scatter_data_size;
141 	wmsum_t abdstat_scatter_chunk_waste;
142 	wmsum_t abdstat_scatter_orders[MAX_ORDER];
143 	wmsum_t abdstat_scatter_page_multi_chunk;
144 	wmsum_t abdstat_scatter_page_multi_zone;
145 	wmsum_t abdstat_scatter_page_alloc_retry;
146 	wmsum_t abdstat_scatter_sg_table_retry;
147 } abd_sums;
148 
149 #define	abd_for_each_sg(abd, sg, n, i)	\
150 	for_each_sg(ABD_SCATTER(abd).abd_sgl, sg, n, i)
151 
152 /*
153  * zfs_abd_scatter_min_size is the minimum allocation size to use scatter
154  * ABD's.  Smaller allocations will use linear ABD's which uses
155  * zio_[data_]buf_alloc().
156  *
157  * Scatter ABD's use at least one page each, so sub-page allocations waste
158  * some space when allocated as scatter (e.g. 2KB scatter allocation wastes
159  * half of each page).  Using linear ABD's for small allocations means that
160  * they will be put on slabs which contain many allocations.  This can
161  * improve memory efficiency, but it also makes it much harder for ARC
162  * evictions to actually free pages, because all the buffers on one slab need
163  * to be freed in order for the slab (and underlying pages) to be freed.
164  * Typically, 512B and 1KB kmem caches have 16 buffers per slab, so it's
165  * possible for them to actually waste more memory than scatter (one page per
166  * buf = wasting 3/4 or 7/8th; one buf per slab = wasting 15/16th).
167  *
168  * Spill blocks are typically 512B and are heavily used on systems running
169  * selinux with the default dnode size and the `xattr=sa` property set.
170  *
171  * By default we use linear allocations for 512B and 1KB, and scatter
172  * allocations for larger (1.5KB and up).
173  */
174 static int zfs_abd_scatter_min_size = 512 * 3;
175 
176 /*
177  * We use a scattered SPA_MAXBLOCKSIZE sized ABD whose pages are
178  * just a single zero'd page. This allows us to conserve memory by
179  * only using a single zero page for the scatterlist.
180  */
181 abd_t *abd_zero_scatter = NULL;
182 
183 struct page;
184 /*
185  * _KERNEL   - Will point to ZERO_PAGE if it is available or it will be
186  *             an allocated zero'd PAGESIZE buffer.
187  * Userspace - Will be an allocated zero'ed PAGESIZE buffer.
188  *
189  * abd_zero_page is assigned to each of the pages of abd_zero_scatter.
190  */
191 static struct page *abd_zero_page = NULL;
192 
193 static kmem_cache_t *abd_cache = NULL;
194 static kstat_t *abd_ksp;
195 
196 static uint_t
197 abd_chunkcnt_for_bytes(size_t size)
198 {
199 	return (P2ROUNDUP(size, PAGESIZE) / PAGESIZE);
200 }
201 
202 abd_t *
203 abd_alloc_struct_impl(size_t size)
204 {
205 	/*
206 	 * In Linux we do not use the size passed in during ABD
207 	 * allocation, so we just ignore it.
208 	 */
209 	(void) size;
210 	abd_t *abd = kmem_cache_alloc(abd_cache, KM_PUSHPAGE);
211 	ASSERT3P(abd, !=, NULL);
212 	ABDSTAT_INCR(abdstat_struct_size, sizeof (abd_t));
213 
214 	return (abd);
215 }
216 
217 void
218 abd_free_struct_impl(abd_t *abd)
219 {
220 	kmem_cache_free(abd_cache, abd);
221 	ABDSTAT_INCR(abdstat_struct_size, -(int)sizeof (abd_t));
222 }
223 
224 #ifdef _KERNEL
225 static unsigned zfs_abd_scatter_max_order = MAX_ORDER - 1;
226 
227 /*
228  * Mark zfs data pages so they can be excluded from kernel crash dumps
229  */
230 #ifdef _LP64
231 #define	ABD_FILE_CACHE_PAGE	0x2F5ABDF11ECAC4E
232 
233 static inline void
234 abd_mark_zfs_page(struct page *page)
235 {
236 	get_page(page);
237 	SetPagePrivate(page);
238 	set_page_private(page, ABD_FILE_CACHE_PAGE);
239 }
240 
241 static inline void
242 abd_unmark_zfs_page(struct page *page)
243 {
244 	set_page_private(page, 0UL);
245 	ClearPagePrivate(page);
246 	put_page(page);
247 }
248 #else
249 #define	abd_mark_zfs_page(page)
250 #define	abd_unmark_zfs_page(page)
251 #endif /* _LP64 */
252 
253 #ifndef CONFIG_HIGHMEM
254 
255 #ifndef __GFP_RECLAIM
256 #define	__GFP_RECLAIM		__GFP_WAIT
257 #endif
258 
259 /*
260  * The goal is to minimize fragmentation by preferentially populating ABDs
261  * with higher order compound pages from a single zone.  Allocation size is
262  * progressively decreased until it can be satisfied without performing
263  * reclaim or compaction.  When necessary this function will degenerate to
264  * allocating individual pages and allowing reclaim to satisfy allocations.
265  */
266 void
267 abd_alloc_chunks(abd_t *abd, size_t size)
268 {
269 	struct list_head pages;
270 	struct sg_table table;
271 	struct scatterlist *sg;
272 	struct page *page, *tmp_page = NULL;
273 	gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
274 	gfp_t gfp_comp = (gfp | __GFP_NORETRY | __GFP_COMP) & ~__GFP_RECLAIM;
275 	int max_order = MIN(zfs_abd_scatter_max_order, MAX_ORDER - 1);
276 	int nr_pages = abd_chunkcnt_for_bytes(size);
277 	int chunks = 0, zones = 0;
278 	size_t remaining_size;
279 	int nid = NUMA_NO_NODE;
280 	int alloc_pages = 0;
281 
282 	INIT_LIST_HEAD(&pages);
283 
284 	while (alloc_pages < nr_pages) {
285 		unsigned chunk_pages;
286 		int order;
287 
288 		order = MIN(highbit64(nr_pages - alloc_pages) - 1, max_order);
289 		chunk_pages = (1U << order);
290 
291 		page = alloc_pages_node(nid, order ? gfp_comp : gfp, order);
292 		if (page == NULL) {
293 			if (order == 0) {
294 				ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
295 				schedule_timeout_interruptible(1);
296 			} else {
297 				max_order = MAX(0, order - 1);
298 			}
299 			continue;
300 		}
301 
302 		list_add_tail(&page->lru, &pages);
303 
304 		if ((nid != NUMA_NO_NODE) && (page_to_nid(page) != nid))
305 			zones++;
306 
307 		nid = page_to_nid(page);
308 		ABDSTAT_BUMP(abdstat_scatter_orders[order]);
309 		chunks++;
310 		alloc_pages += chunk_pages;
311 	}
312 
313 	ASSERT3S(alloc_pages, ==, nr_pages);
314 
315 	while (sg_alloc_table(&table, chunks, gfp)) {
316 		ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
317 		schedule_timeout_interruptible(1);
318 	}
319 
320 	sg = table.sgl;
321 	remaining_size = size;
322 	list_for_each_entry_safe(page, tmp_page, &pages, lru) {
323 		size_t sg_size = MIN(PAGESIZE << compound_order(page),
324 		    remaining_size);
325 		sg_set_page(sg, page, sg_size, 0);
326 		abd_mark_zfs_page(page);
327 		remaining_size -= sg_size;
328 
329 		sg = sg_next(sg);
330 		list_del(&page->lru);
331 	}
332 
333 	/*
334 	 * These conditions ensure that a possible transformation to a linear
335 	 * ABD would be valid.
336 	 */
337 	ASSERT(!PageHighMem(sg_page(table.sgl)));
338 	ASSERT0(ABD_SCATTER(abd).abd_offset);
339 
340 	if (table.nents == 1) {
341 		/*
342 		 * Since there is only one entry, this ABD can be represented
343 		 * as a linear buffer.  All single-page (4K) ABD's can be
344 		 * represented this way.  Some multi-page ABD's can also be
345 		 * represented this way, if we were able to allocate a single
346 		 * "chunk" (higher-order "page" which represents a power-of-2
347 		 * series of physically-contiguous pages).  This is often the
348 		 * case for 2-page (8K) ABD's.
349 		 *
350 		 * Representing a single-entry scatter ABD as a linear ABD
351 		 * has the performance advantage of avoiding the copy (and
352 		 * allocation) in abd_borrow_buf_copy / abd_return_buf_copy.
353 		 * A performance increase of around 5% has been observed for
354 		 * ARC-cached reads (of small blocks which can take advantage
355 		 * of this).
356 		 *
357 		 * Note that this optimization is only possible because the
358 		 * pages are always mapped into the kernel's address space.
359 		 * This is not the case for highmem pages, so the
360 		 * optimization can not be made there.
361 		 */
362 		abd->abd_flags |= ABD_FLAG_LINEAR;
363 		abd->abd_flags |= ABD_FLAG_LINEAR_PAGE;
364 		abd->abd_u.abd_linear.abd_sgl = table.sgl;
365 		ABD_LINEAR_BUF(abd) = page_address(sg_page(table.sgl));
366 	} else if (table.nents > 1) {
367 		ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
368 		abd->abd_flags |= ABD_FLAG_MULTI_CHUNK;
369 
370 		if (zones) {
371 			ABDSTAT_BUMP(abdstat_scatter_page_multi_zone);
372 			abd->abd_flags |= ABD_FLAG_MULTI_ZONE;
373 		}
374 
375 		ABD_SCATTER(abd).abd_sgl = table.sgl;
376 		ABD_SCATTER(abd).abd_nents = table.nents;
377 	}
378 }
379 #else
380 
381 /*
382  * Allocate N individual pages to construct a scatter ABD.  This function
383  * makes no attempt to request contiguous pages and requires the minimal
384  * number of kernel interfaces.  It's designed for maximum compatibility.
385  */
386 void
387 abd_alloc_chunks(abd_t *abd, size_t size)
388 {
389 	struct scatterlist *sg = NULL;
390 	struct sg_table table;
391 	struct page *page;
392 	gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
393 	int nr_pages = abd_chunkcnt_for_bytes(size);
394 	int i = 0;
395 
396 	while (sg_alloc_table(&table, nr_pages, gfp)) {
397 		ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
398 		schedule_timeout_interruptible(1);
399 	}
400 
401 	ASSERT3U(table.nents, ==, nr_pages);
402 	ABD_SCATTER(abd).abd_sgl = table.sgl;
403 	ABD_SCATTER(abd).abd_nents = nr_pages;
404 
405 	abd_for_each_sg(abd, sg, nr_pages, i) {
406 		while ((page = __page_cache_alloc(gfp)) == NULL) {
407 			ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
408 			schedule_timeout_interruptible(1);
409 		}
410 
411 		ABDSTAT_BUMP(abdstat_scatter_orders[0]);
412 		sg_set_page(sg, page, PAGESIZE, 0);
413 		abd_mark_zfs_page(page);
414 	}
415 
416 	if (nr_pages > 1) {
417 		ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
418 		abd->abd_flags |= ABD_FLAG_MULTI_CHUNK;
419 	}
420 }
421 #endif /* !CONFIG_HIGHMEM */
422 
423 /*
424  * This must be called if any of the sg_table allocation functions
425  * are called.
426  */
427 static void
428 abd_free_sg_table(abd_t *abd)
429 {
430 	struct sg_table table;
431 
432 	table.sgl = ABD_SCATTER(abd).abd_sgl;
433 	table.nents = table.orig_nents = ABD_SCATTER(abd).abd_nents;
434 	sg_free_table(&table);
435 }
436 
437 void
438 abd_free_chunks(abd_t *abd)
439 {
440 	struct scatterlist *sg = NULL;
441 	struct page *page;
442 	int nr_pages = ABD_SCATTER(abd).abd_nents;
443 	int order, i = 0;
444 
445 	if (abd->abd_flags & ABD_FLAG_MULTI_ZONE)
446 		ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_zone);
447 
448 	if (abd->abd_flags & ABD_FLAG_MULTI_CHUNK)
449 		ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_chunk);
450 
451 	abd_for_each_sg(abd, sg, nr_pages, i) {
452 		page = sg_page(sg);
453 		abd_unmark_zfs_page(page);
454 		order = compound_order(page);
455 		__free_pages(page, order);
456 		ASSERT3U(sg->length, <=, PAGE_SIZE << order);
457 		ABDSTAT_BUMPDOWN(abdstat_scatter_orders[order]);
458 	}
459 	abd_free_sg_table(abd);
460 }
461 
462 /*
463  * Allocate scatter ABD of size SPA_MAXBLOCKSIZE, where each page in
464  * the scatterlist will be set to the zero'd out buffer abd_zero_page.
465  */
466 static void
467 abd_alloc_zero_scatter(void)
468 {
469 	struct scatterlist *sg = NULL;
470 	struct sg_table table;
471 	gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
472 	int nr_pages = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE);
473 	int i = 0;
474 
475 #if defined(HAVE_ZERO_PAGE_GPL_ONLY)
476 	gfp_t gfp_zero_page = gfp | __GFP_ZERO;
477 	while ((abd_zero_page = __page_cache_alloc(gfp_zero_page)) == NULL) {
478 		ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
479 		schedule_timeout_interruptible(1);
480 	}
481 	abd_mark_zfs_page(abd_zero_page);
482 #else
483 	abd_zero_page = ZERO_PAGE(0);
484 #endif /* HAVE_ZERO_PAGE_GPL_ONLY */
485 
486 	while (sg_alloc_table(&table, nr_pages, gfp)) {
487 		ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
488 		schedule_timeout_interruptible(1);
489 	}
490 	ASSERT3U(table.nents, ==, nr_pages);
491 
492 	abd_zero_scatter = abd_alloc_struct(SPA_MAXBLOCKSIZE);
493 	abd_zero_scatter->abd_flags |= ABD_FLAG_OWNER;
494 	ABD_SCATTER(abd_zero_scatter).abd_offset = 0;
495 	ABD_SCATTER(abd_zero_scatter).abd_sgl = table.sgl;
496 	ABD_SCATTER(abd_zero_scatter).abd_nents = nr_pages;
497 	abd_zero_scatter->abd_size = SPA_MAXBLOCKSIZE;
498 	abd_zero_scatter->abd_flags |= ABD_FLAG_MULTI_CHUNK | ABD_FLAG_ZEROS;
499 
500 	abd_for_each_sg(abd_zero_scatter, sg, nr_pages, i) {
501 		sg_set_page(sg, abd_zero_page, PAGESIZE, 0);
502 	}
503 
504 	ABDSTAT_BUMP(abdstat_scatter_cnt);
505 	ABDSTAT_INCR(abdstat_scatter_data_size, PAGESIZE);
506 	ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
507 }
508 
509 #else /* _KERNEL */
510 
511 #ifndef PAGE_SHIFT
512 #define	PAGE_SHIFT (highbit64(PAGESIZE)-1)
513 #endif
514 
515 #define	zfs_kmap_atomic(chunk)		((void *)chunk)
516 #define	zfs_kunmap_atomic(addr)		do { (void)(addr); } while (0)
517 #define	local_irq_save(flags)		do { (void)(flags); } while (0)
518 #define	local_irq_restore(flags)	do { (void)(flags); } while (0)
519 #define	nth_page(pg, i) \
520 	((struct page *)((void *)(pg) + (i) * PAGESIZE))
521 
522 struct scatterlist {
523 	struct page *page;
524 	int length;
525 	int end;
526 };
527 
528 static void
529 sg_init_table(struct scatterlist *sg, int nr)
530 {
531 	memset(sg, 0, nr * sizeof (struct scatterlist));
532 	sg[nr - 1].end = 1;
533 }
534 
535 /*
536  * This must be called if any of the sg_table allocation functions
537  * are called.
538  */
539 static void
540 abd_free_sg_table(abd_t *abd)
541 {
542 	int nents = ABD_SCATTER(abd).abd_nents;
543 	vmem_free(ABD_SCATTER(abd).abd_sgl,
544 	    nents * sizeof (struct scatterlist));
545 }
546 
547 #define	for_each_sg(sgl, sg, nr, i)	\
548 	for ((i) = 0, (sg) = (sgl); (i) < (nr); (i)++, (sg) = sg_next(sg))
549 
550 static inline void
551 sg_set_page(struct scatterlist *sg, struct page *page, unsigned int len,
552     unsigned int offset)
553 {
554 	/* currently we don't use offset */
555 	ASSERT(offset == 0);
556 	sg->page = page;
557 	sg->length = len;
558 }
559 
560 static inline struct page *
561 sg_page(struct scatterlist *sg)
562 {
563 	return (sg->page);
564 }
565 
566 static inline struct scatterlist *
567 sg_next(struct scatterlist *sg)
568 {
569 	if (sg->end)
570 		return (NULL);
571 
572 	return (sg + 1);
573 }
574 
575 void
576 abd_alloc_chunks(abd_t *abd, size_t size)
577 {
578 	unsigned nr_pages = abd_chunkcnt_for_bytes(size);
579 	struct scatterlist *sg;
580 	int i;
581 
582 	ABD_SCATTER(abd).abd_sgl = vmem_alloc(nr_pages *
583 	    sizeof (struct scatterlist), KM_SLEEP);
584 	sg_init_table(ABD_SCATTER(abd).abd_sgl, nr_pages);
585 
586 	abd_for_each_sg(abd, sg, nr_pages, i) {
587 		struct page *p = umem_alloc_aligned(PAGESIZE, 64, KM_SLEEP);
588 		sg_set_page(sg, p, PAGESIZE, 0);
589 	}
590 	ABD_SCATTER(abd).abd_nents = nr_pages;
591 }
592 
593 void
594 abd_free_chunks(abd_t *abd)
595 {
596 	int i, n = ABD_SCATTER(abd).abd_nents;
597 	struct scatterlist *sg;
598 
599 	abd_for_each_sg(abd, sg, n, i) {
600 		for (int j = 0; j < sg->length; j += PAGESIZE) {
601 			struct page *p = nth_page(sg_page(sg), j >> PAGE_SHIFT);
602 			umem_free(p, PAGESIZE);
603 		}
604 	}
605 	abd_free_sg_table(abd);
606 }
607 
608 static void
609 abd_alloc_zero_scatter(void)
610 {
611 	unsigned nr_pages = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE);
612 	struct scatterlist *sg;
613 	int i;
614 
615 	abd_zero_page = umem_alloc_aligned(PAGESIZE, 64, KM_SLEEP);
616 	memset(abd_zero_page, 0, PAGESIZE);
617 	abd_zero_scatter = abd_alloc_struct(SPA_MAXBLOCKSIZE);
618 	abd_zero_scatter->abd_flags |= ABD_FLAG_OWNER;
619 	abd_zero_scatter->abd_flags |= ABD_FLAG_MULTI_CHUNK | ABD_FLAG_ZEROS;
620 	ABD_SCATTER(abd_zero_scatter).abd_offset = 0;
621 	ABD_SCATTER(abd_zero_scatter).abd_nents = nr_pages;
622 	abd_zero_scatter->abd_size = SPA_MAXBLOCKSIZE;
623 	ABD_SCATTER(abd_zero_scatter).abd_sgl = vmem_alloc(nr_pages *
624 	    sizeof (struct scatterlist), KM_SLEEP);
625 
626 	sg_init_table(ABD_SCATTER(abd_zero_scatter).abd_sgl, nr_pages);
627 
628 	abd_for_each_sg(abd_zero_scatter, sg, nr_pages, i) {
629 		sg_set_page(sg, abd_zero_page, PAGESIZE, 0);
630 	}
631 
632 	ABDSTAT_BUMP(abdstat_scatter_cnt);
633 	ABDSTAT_INCR(abdstat_scatter_data_size, PAGESIZE);
634 	ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk);
635 }
636 
637 #endif /* _KERNEL */
638 
639 boolean_t
640 abd_size_alloc_linear(size_t size)
641 {
642 	return (!zfs_abd_scatter_enabled || size < zfs_abd_scatter_min_size);
643 }
644 
645 void
646 abd_update_scatter_stats(abd_t *abd, abd_stats_op_t op)
647 {
648 	ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR);
649 	int waste = P2ROUNDUP(abd->abd_size, PAGESIZE) - abd->abd_size;
650 	if (op == ABDSTAT_INCR) {
651 		ABDSTAT_BUMP(abdstat_scatter_cnt);
652 		ABDSTAT_INCR(abdstat_scatter_data_size, abd->abd_size);
653 		ABDSTAT_INCR(abdstat_scatter_chunk_waste, waste);
654 		arc_space_consume(waste, ARC_SPACE_ABD_CHUNK_WASTE);
655 	} else {
656 		ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
657 		ABDSTAT_INCR(abdstat_scatter_data_size, -(int)abd->abd_size);
658 		ABDSTAT_INCR(abdstat_scatter_chunk_waste, -waste);
659 		arc_space_return(waste, ARC_SPACE_ABD_CHUNK_WASTE);
660 	}
661 }
662 
663 void
664 abd_update_linear_stats(abd_t *abd, abd_stats_op_t op)
665 {
666 	ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR);
667 	if (op == ABDSTAT_INCR) {
668 		ABDSTAT_BUMP(abdstat_linear_cnt);
669 		ABDSTAT_INCR(abdstat_linear_data_size, abd->abd_size);
670 	} else {
671 		ABDSTAT_BUMPDOWN(abdstat_linear_cnt);
672 		ABDSTAT_INCR(abdstat_linear_data_size, -(int)abd->abd_size);
673 	}
674 }
675 
676 void
677 abd_verify_scatter(abd_t *abd)
678 {
679 	size_t n;
680 	int i = 0;
681 	struct scatterlist *sg = NULL;
682 
683 	ASSERT3U(ABD_SCATTER(abd).abd_nents, >, 0);
684 	ASSERT3U(ABD_SCATTER(abd).abd_offset, <,
685 	    ABD_SCATTER(abd).abd_sgl->length);
686 	n = ABD_SCATTER(abd).abd_nents;
687 	abd_for_each_sg(abd, sg, n, i) {
688 		ASSERT3P(sg_page(sg), !=, NULL);
689 	}
690 }
691 
692 static void
693 abd_free_zero_scatter(void)
694 {
695 	ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
696 	ABDSTAT_INCR(abdstat_scatter_data_size, -(int)PAGESIZE);
697 	ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_chunk);
698 
699 	abd_free_sg_table(abd_zero_scatter);
700 	abd_free_struct(abd_zero_scatter);
701 	abd_zero_scatter = NULL;
702 	ASSERT3P(abd_zero_page, !=, NULL);
703 #if defined(_KERNEL)
704 #if defined(HAVE_ZERO_PAGE_GPL_ONLY)
705 	abd_unmark_zfs_page(abd_zero_page);
706 	__free_page(abd_zero_page);
707 #endif /* HAVE_ZERO_PAGE_GPL_ONLY */
708 #else
709 	umem_free(abd_zero_page, PAGESIZE);
710 #endif /* _KERNEL */
711 }
712 
713 static int
714 abd_kstats_update(kstat_t *ksp, int rw)
715 {
716 	abd_stats_t *as = ksp->ks_data;
717 
718 	if (rw == KSTAT_WRITE)
719 		return (EACCES);
720 	as->abdstat_struct_size.value.ui64 =
721 	    wmsum_value(&abd_sums.abdstat_struct_size);
722 	as->abdstat_linear_cnt.value.ui64 =
723 	    wmsum_value(&abd_sums.abdstat_linear_cnt);
724 	as->abdstat_linear_data_size.value.ui64 =
725 	    wmsum_value(&abd_sums.abdstat_linear_data_size);
726 	as->abdstat_scatter_cnt.value.ui64 =
727 	    wmsum_value(&abd_sums.abdstat_scatter_cnt);
728 	as->abdstat_scatter_data_size.value.ui64 =
729 	    wmsum_value(&abd_sums.abdstat_scatter_data_size);
730 	as->abdstat_scatter_chunk_waste.value.ui64 =
731 	    wmsum_value(&abd_sums.abdstat_scatter_chunk_waste);
732 	for (int i = 0; i < MAX_ORDER; i++) {
733 		as->abdstat_scatter_orders[i].value.ui64 =
734 		    wmsum_value(&abd_sums.abdstat_scatter_orders[i]);
735 	}
736 	as->abdstat_scatter_page_multi_chunk.value.ui64 =
737 	    wmsum_value(&abd_sums.abdstat_scatter_page_multi_chunk);
738 	as->abdstat_scatter_page_multi_zone.value.ui64 =
739 	    wmsum_value(&abd_sums.abdstat_scatter_page_multi_zone);
740 	as->abdstat_scatter_page_alloc_retry.value.ui64 =
741 	    wmsum_value(&abd_sums.abdstat_scatter_page_alloc_retry);
742 	as->abdstat_scatter_sg_table_retry.value.ui64 =
743 	    wmsum_value(&abd_sums.abdstat_scatter_sg_table_retry);
744 	return (0);
745 }
746 
747 void
748 abd_init(void)
749 {
750 	int i;
751 
752 	abd_cache = kmem_cache_create("abd_t", sizeof (abd_t),
753 	    0, NULL, NULL, NULL, NULL, NULL, 0);
754 
755 	wmsum_init(&abd_sums.abdstat_struct_size, 0);
756 	wmsum_init(&abd_sums.abdstat_linear_cnt, 0);
757 	wmsum_init(&abd_sums.abdstat_linear_data_size, 0);
758 	wmsum_init(&abd_sums.abdstat_scatter_cnt, 0);
759 	wmsum_init(&abd_sums.abdstat_scatter_data_size, 0);
760 	wmsum_init(&abd_sums.abdstat_scatter_chunk_waste, 0);
761 	for (i = 0; i < MAX_ORDER; i++)
762 		wmsum_init(&abd_sums.abdstat_scatter_orders[i], 0);
763 	wmsum_init(&abd_sums.abdstat_scatter_page_multi_chunk, 0);
764 	wmsum_init(&abd_sums.abdstat_scatter_page_multi_zone, 0);
765 	wmsum_init(&abd_sums.abdstat_scatter_page_alloc_retry, 0);
766 	wmsum_init(&abd_sums.abdstat_scatter_sg_table_retry, 0);
767 
768 	abd_ksp = kstat_create("zfs", 0, "abdstats", "misc", KSTAT_TYPE_NAMED,
769 	    sizeof (abd_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
770 	if (abd_ksp != NULL) {
771 		for (i = 0; i < MAX_ORDER; i++) {
772 			snprintf(abd_stats.abdstat_scatter_orders[i].name,
773 			    KSTAT_STRLEN, "scatter_order_%d", i);
774 			abd_stats.abdstat_scatter_orders[i].data_type =
775 			    KSTAT_DATA_UINT64;
776 		}
777 		abd_ksp->ks_data = &abd_stats;
778 		abd_ksp->ks_update = abd_kstats_update;
779 		kstat_install(abd_ksp);
780 	}
781 
782 	abd_alloc_zero_scatter();
783 }
784 
785 void
786 abd_fini(void)
787 {
788 	abd_free_zero_scatter();
789 
790 	if (abd_ksp != NULL) {
791 		kstat_delete(abd_ksp);
792 		abd_ksp = NULL;
793 	}
794 
795 	wmsum_fini(&abd_sums.abdstat_struct_size);
796 	wmsum_fini(&abd_sums.abdstat_linear_cnt);
797 	wmsum_fini(&abd_sums.abdstat_linear_data_size);
798 	wmsum_fini(&abd_sums.abdstat_scatter_cnt);
799 	wmsum_fini(&abd_sums.abdstat_scatter_data_size);
800 	wmsum_fini(&abd_sums.abdstat_scatter_chunk_waste);
801 	for (int i = 0; i < MAX_ORDER; i++)
802 		wmsum_fini(&abd_sums.abdstat_scatter_orders[i]);
803 	wmsum_fini(&abd_sums.abdstat_scatter_page_multi_chunk);
804 	wmsum_fini(&abd_sums.abdstat_scatter_page_multi_zone);
805 	wmsum_fini(&abd_sums.abdstat_scatter_page_alloc_retry);
806 	wmsum_fini(&abd_sums.abdstat_scatter_sg_table_retry);
807 
808 	if (abd_cache) {
809 		kmem_cache_destroy(abd_cache);
810 		abd_cache = NULL;
811 	}
812 }
813 
814 void
815 abd_free_linear_page(abd_t *abd)
816 {
817 	/* Transform it back into a scatter ABD for freeing */
818 	struct scatterlist *sg = abd->abd_u.abd_linear.abd_sgl;
819 	abd->abd_flags &= ~ABD_FLAG_LINEAR;
820 	abd->abd_flags &= ~ABD_FLAG_LINEAR_PAGE;
821 	ABD_SCATTER(abd).abd_nents = 1;
822 	ABD_SCATTER(abd).abd_offset = 0;
823 	ABD_SCATTER(abd).abd_sgl = sg;
824 	abd_free_chunks(abd);
825 
826 	abd_update_scatter_stats(abd, ABDSTAT_DECR);
827 }
828 
829 /*
830  * If we're going to use this ABD for doing I/O using the block layer, the
831  * consumer of the ABD data doesn't care if it's scattered or not, and we don't
832  * plan to store this ABD in memory for a long period of time, we should
833  * allocate the ABD type that requires the least data copying to do the I/O.
834  *
835  * On Linux the optimal thing to do would be to use abd_get_offset() and
836  * construct a new ABD which shares the original pages thereby eliminating
837  * the copy.  But for the moment a new linear ABD is allocated until this
838  * performance optimization can be implemented.
839  */
840 abd_t *
841 abd_alloc_for_io(size_t size, boolean_t is_metadata)
842 {
843 	return (abd_alloc(size, is_metadata));
844 }
845 
846 abd_t *
847 abd_get_offset_scatter(abd_t *abd, abd_t *sabd, size_t off,
848     size_t size)
849 {
850 	(void) size;
851 	int i = 0;
852 	struct scatterlist *sg = NULL;
853 
854 	abd_verify(sabd);
855 	ASSERT3U(off, <=, sabd->abd_size);
856 
857 	size_t new_offset = ABD_SCATTER(sabd).abd_offset + off;
858 
859 	if (abd == NULL)
860 		abd = abd_alloc_struct(0);
861 
862 	/*
863 	 * Even if this buf is filesystem metadata, we only track that
864 	 * if we own the underlying data buffer, which is not true in
865 	 * this case. Therefore, we don't ever use ABD_FLAG_META here.
866 	 */
867 
868 	abd_for_each_sg(sabd, sg, ABD_SCATTER(sabd).abd_nents, i) {
869 		if (new_offset < sg->length)
870 			break;
871 		new_offset -= sg->length;
872 	}
873 
874 	ABD_SCATTER(abd).abd_sgl = sg;
875 	ABD_SCATTER(abd).abd_offset = new_offset;
876 	ABD_SCATTER(abd).abd_nents = ABD_SCATTER(sabd).abd_nents - i;
877 
878 	return (abd);
879 }
880 
881 /*
882  * Initialize the abd_iter.
883  */
884 void
885 abd_iter_init(struct abd_iter *aiter, abd_t *abd)
886 {
887 	ASSERT(!abd_is_gang(abd));
888 	abd_verify(abd);
889 	aiter->iter_abd = abd;
890 	aiter->iter_mapaddr = NULL;
891 	aiter->iter_mapsize = 0;
892 	aiter->iter_pos = 0;
893 	if (abd_is_linear(abd)) {
894 		aiter->iter_offset = 0;
895 		aiter->iter_sg = NULL;
896 	} else {
897 		aiter->iter_offset = ABD_SCATTER(abd).abd_offset;
898 		aiter->iter_sg = ABD_SCATTER(abd).abd_sgl;
899 	}
900 }
901 
902 /*
903  * This is just a helper function to see if we have exhausted the
904  * abd_iter and reached the end.
905  */
906 boolean_t
907 abd_iter_at_end(struct abd_iter *aiter)
908 {
909 	return (aiter->iter_pos == aiter->iter_abd->abd_size);
910 }
911 
912 /*
913  * Advance the iterator by a certain amount. Cannot be called when a chunk is
914  * in use. This can be safely called when the aiter has already exhausted, in
915  * which case this does nothing.
916  */
917 void
918 abd_iter_advance(struct abd_iter *aiter, size_t amount)
919 {
920 	ASSERT3P(aiter->iter_mapaddr, ==, NULL);
921 	ASSERT0(aiter->iter_mapsize);
922 
923 	/* There's nothing left to advance to, so do nothing */
924 	if (abd_iter_at_end(aiter))
925 		return;
926 
927 	aiter->iter_pos += amount;
928 	aiter->iter_offset += amount;
929 	if (!abd_is_linear(aiter->iter_abd)) {
930 		while (aiter->iter_offset >= aiter->iter_sg->length) {
931 			aiter->iter_offset -= aiter->iter_sg->length;
932 			aiter->iter_sg = sg_next(aiter->iter_sg);
933 			if (aiter->iter_sg == NULL) {
934 				ASSERT0(aiter->iter_offset);
935 				break;
936 			}
937 		}
938 	}
939 }
940 
941 /*
942  * Map the current chunk into aiter. This can be safely called when the aiter
943  * has already exhausted, in which case this does nothing.
944  */
945 void
946 abd_iter_map(struct abd_iter *aiter)
947 {
948 	void *paddr;
949 	size_t offset = 0;
950 
951 	ASSERT3P(aiter->iter_mapaddr, ==, NULL);
952 	ASSERT0(aiter->iter_mapsize);
953 
954 	/* There's nothing left to iterate over, so do nothing */
955 	if (abd_iter_at_end(aiter))
956 		return;
957 
958 	if (abd_is_linear(aiter->iter_abd)) {
959 		ASSERT3U(aiter->iter_pos, ==, aiter->iter_offset);
960 		offset = aiter->iter_offset;
961 		aiter->iter_mapsize = aiter->iter_abd->abd_size - offset;
962 		paddr = ABD_LINEAR_BUF(aiter->iter_abd);
963 	} else {
964 		offset = aiter->iter_offset;
965 		aiter->iter_mapsize = MIN(aiter->iter_sg->length - offset,
966 		    aiter->iter_abd->abd_size - aiter->iter_pos);
967 
968 		paddr = zfs_kmap_atomic(sg_page(aiter->iter_sg));
969 	}
970 
971 	aiter->iter_mapaddr = (char *)paddr + offset;
972 }
973 
974 /*
975  * Unmap the current chunk from aiter. This can be safely called when the aiter
976  * has already exhausted, in which case this does nothing.
977  */
978 void
979 abd_iter_unmap(struct abd_iter *aiter)
980 {
981 	/* There's nothing left to unmap, so do nothing */
982 	if (abd_iter_at_end(aiter))
983 		return;
984 
985 	if (!abd_is_linear(aiter->iter_abd)) {
986 		/* LINTED E_FUNC_SET_NOT_USED */
987 		zfs_kunmap_atomic(aiter->iter_mapaddr - aiter->iter_offset);
988 	}
989 
990 	ASSERT3P(aiter->iter_mapaddr, !=, NULL);
991 	ASSERT3U(aiter->iter_mapsize, >, 0);
992 
993 	aiter->iter_mapaddr = NULL;
994 	aiter->iter_mapsize = 0;
995 }
996 
997 void
998 abd_cache_reap_now(void)
999 {
1000 }
1001 
1002 #if defined(_KERNEL)
1003 /*
1004  * bio_nr_pages for ABD.
1005  * @off is the offset in @abd
1006  */
1007 unsigned long
1008 abd_nr_pages_off(abd_t *abd, unsigned int size, size_t off)
1009 {
1010 	unsigned long pos;
1011 
1012 	if (abd_is_gang(abd)) {
1013 		unsigned long count = 0;
1014 
1015 		for (abd_t *cabd = abd_gang_get_offset(abd, &off);
1016 		    cabd != NULL && size != 0;
1017 		    cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) {
1018 			ASSERT3U(off, <, cabd->abd_size);
1019 			int mysize = MIN(size, cabd->abd_size - off);
1020 			count += abd_nr_pages_off(cabd, mysize, off);
1021 			size -= mysize;
1022 			off = 0;
1023 		}
1024 		return (count);
1025 	}
1026 
1027 	if (abd_is_linear(abd))
1028 		pos = (unsigned long)abd_to_buf(abd) + off;
1029 	else
1030 		pos = ABD_SCATTER(abd).abd_offset + off;
1031 
1032 	return (((pos + size + PAGESIZE - 1) >> PAGE_SHIFT) -
1033 	    (pos >> PAGE_SHIFT));
1034 }
1035 
1036 static unsigned int
1037 bio_map(struct bio *bio, void *buf_ptr, unsigned int bio_size)
1038 {
1039 	unsigned int offset, size, i;
1040 	struct page *page;
1041 
1042 	offset = offset_in_page(buf_ptr);
1043 	for (i = 0; i < bio->bi_max_vecs; i++) {
1044 		size = PAGE_SIZE - offset;
1045 
1046 		if (bio_size <= 0)
1047 			break;
1048 
1049 		if (size > bio_size)
1050 			size = bio_size;
1051 
1052 		if (is_vmalloc_addr(buf_ptr))
1053 			page = vmalloc_to_page(buf_ptr);
1054 		else
1055 			page = virt_to_page(buf_ptr);
1056 
1057 		/*
1058 		 * Some network related block device uses tcp_sendpage, which
1059 		 * doesn't behave well when using 0-count page, this is a
1060 		 * safety net to catch them.
1061 		 */
1062 		ASSERT3S(page_count(page), >, 0);
1063 
1064 		if (bio_add_page(bio, page, size, offset) != size)
1065 			break;
1066 
1067 		buf_ptr += size;
1068 		bio_size -= size;
1069 		offset = 0;
1070 	}
1071 
1072 	return (bio_size);
1073 }
1074 
1075 /*
1076  * bio_map for gang ABD.
1077  */
1078 static unsigned int
1079 abd_gang_bio_map_off(struct bio *bio, abd_t *abd,
1080     unsigned int io_size, size_t off)
1081 {
1082 	ASSERT(abd_is_gang(abd));
1083 
1084 	for (abd_t *cabd = abd_gang_get_offset(abd, &off);
1085 	    cabd != NULL;
1086 	    cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) {
1087 		ASSERT3U(off, <, cabd->abd_size);
1088 		int size = MIN(io_size, cabd->abd_size - off);
1089 		int remainder = abd_bio_map_off(bio, cabd, size, off);
1090 		io_size -= (size - remainder);
1091 		if (io_size == 0 || remainder > 0)
1092 			return (io_size);
1093 		off = 0;
1094 	}
1095 	ASSERT0(io_size);
1096 	return (io_size);
1097 }
1098 
1099 /*
1100  * bio_map for ABD.
1101  * @off is the offset in @abd
1102  * Remaining IO size is returned
1103  */
1104 unsigned int
1105 abd_bio_map_off(struct bio *bio, abd_t *abd,
1106     unsigned int io_size, size_t off)
1107 {
1108 	struct abd_iter aiter;
1109 
1110 	ASSERT3U(io_size, <=, abd->abd_size - off);
1111 	if (abd_is_linear(abd))
1112 		return (bio_map(bio, ((char *)abd_to_buf(abd)) + off, io_size));
1113 
1114 	ASSERT(!abd_is_linear(abd));
1115 	if (abd_is_gang(abd))
1116 		return (abd_gang_bio_map_off(bio, abd, io_size, off));
1117 
1118 	abd_iter_init(&aiter, abd);
1119 	abd_iter_advance(&aiter, off);
1120 
1121 	for (int i = 0; i < bio->bi_max_vecs; i++) {
1122 		struct page *pg;
1123 		size_t len, sgoff, pgoff;
1124 		struct scatterlist *sg;
1125 
1126 		if (io_size <= 0)
1127 			break;
1128 
1129 		sg = aiter.iter_sg;
1130 		sgoff = aiter.iter_offset;
1131 		pgoff = sgoff & (PAGESIZE - 1);
1132 		len = MIN(io_size, PAGESIZE - pgoff);
1133 		ASSERT(len > 0);
1134 
1135 		pg = nth_page(sg_page(sg), sgoff >> PAGE_SHIFT);
1136 		if (bio_add_page(bio, pg, len, pgoff) != len)
1137 			break;
1138 
1139 		io_size -= len;
1140 		abd_iter_advance(&aiter, len);
1141 	}
1142 
1143 	return (io_size);
1144 }
1145 
1146 /* Tunable Parameters */
1147 module_param(zfs_abd_scatter_enabled, int, 0644);
1148 MODULE_PARM_DESC(zfs_abd_scatter_enabled,
1149 	"Toggle whether ABD allocations must be linear.");
1150 module_param(zfs_abd_scatter_min_size, int, 0644);
1151 MODULE_PARM_DESC(zfs_abd_scatter_min_size,
1152 	"Minimum size of scatter allocations.");
1153 /* CSTYLED */
1154 module_param(zfs_abd_scatter_max_order, uint, 0644);
1155 MODULE_PARM_DESC(zfs_abd_scatter_max_order,
1156 	"Maximum order allocation used for a scatter ABD.");
1157 #endif
1158