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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (C) 2021-2023 Oracle. All Rights Reserved.
4 * Author: Darrick J. Wong <djwong@kernel.org>
5 */
6#include "xfs.h"
7#include "xfs_fs.h"
8#include "xfs_shared.h"
9#include "xfs_format.h"
10#include "scrub/xfile.h"
11#include "scrub/xfarray.h"
12#include "scrub/scrub.h"
13#include "scrub/trace.h"
14
15/*
16 * Large Arrays of Fixed-Size Records
17 * ==================================
18 *
19 * This memory array uses an xfile (which itself is a memfd "file") to store
20 * large numbers of fixed-size records in memory that can be paged out. This
21 * puts less stress on the memory reclaim algorithms during an online repair
22 * because we don't have to pin so much memory. However, array access is less
23 * direct than would be in a regular memory array. Access to the array is
24 * performed via indexed load and store methods, and an append method is
25 * provided for convenience. Array elements can be unset, which sets them to
26 * all zeroes. Unset entries are skipped during iteration, though direct loads
27 * will return a zeroed buffer. Callers are responsible for concurrency
28 * control.
29 */
30
31/*
32 * Pointer to scratch space. Because we can't access the xfile data directly,
33 * we allocate a small amount of memory on the end of the xfarray structure to
34 * buffer array items when we need space to store values temporarily.
35 */
36static inline void *xfarray_scratch(struct xfarray *array)
37{
38 return (array + 1);
39}
40
41/* Compute array index given an xfile offset. */
42static xfarray_idx_t
43xfarray_idx(
44 struct xfarray *array,
45 loff_t pos)
46{
47 if (array->obj_size_log >= 0)
48 return (xfarray_idx_t)pos >> array->obj_size_log;
49
50 return div_u64((xfarray_idx_t)pos, array->obj_size);
51}
52
53/* Compute xfile offset of array element. */
54static inline loff_t xfarray_pos(struct xfarray *array, xfarray_idx_t idx)
55{
56 if (array->obj_size_log >= 0)
57 return idx << array->obj_size_log;
58
59 return idx * array->obj_size;
60}
61
62/*
63 * Initialize a big memory array. Array records cannot be larger than a
64 * page, and the array cannot span more bytes than the page cache supports.
65 * If @required_capacity is nonzero, the maximum array size will be set to this
66 * quantity and the array creation will fail if the underlying storage cannot
67 * support that many records.
68 */
69int
70xfarray_create(
71 const char *description,
72 unsigned long long required_capacity,
73 size_t obj_size,
74 struct xfarray **arrayp)
75{
76 struct xfarray *array;
77 struct xfile *xfile;
78 int error;
79
80 ASSERT(obj_size < PAGE_SIZE);
81
82 error = xfile_create(description, 0, &xfile);
83 if (error)
84 return error;
85
86 error = -ENOMEM;
87 array = kzalloc(sizeof(struct xfarray) + obj_size, XCHK_GFP_FLAGS);
88 if (!array)
89 goto out_xfile;
90
91 array->xfile = xfile;
92 array->obj_size = obj_size;
93
94 if (is_power_of_2(obj_size))
95 array->obj_size_log = ilog2(obj_size);
96 else
97 array->obj_size_log = -1;
98
99 array->max_nr = xfarray_idx(array, MAX_LFS_FILESIZE);
100 trace_xfarray_create(array, required_capacity);
101
102 if (required_capacity > 0) {
103 if (array->max_nr < required_capacity) {
104 error = -ENOMEM;
105 goto out_xfarray;
106 }
107 array->max_nr = required_capacity;
108 }
109
110 *arrayp = array;
111 return 0;
112
113out_xfarray:
114 kfree(array);
115out_xfile:
116 xfile_destroy(xfile);
117 return error;
118}
119
120/* Destroy the array. */
121void
122xfarray_destroy(
123 struct xfarray *array)
124{
125 xfile_destroy(array->xfile);
126 kfree(array);
127}
128
129/* Load an element from the array. */
130int
131xfarray_load(
132 struct xfarray *array,
133 xfarray_idx_t idx,
134 void *ptr)
135{
136 if (idx >= array->nr)
137 return -ENODATA;
138
139 return xfile_obj_load(array->xfile, ptr, array->obj_size,
140 xfarray_pos(array, idx));
141}
142
143/* Is this array element potentially unset? */
144static inline bool
145xfarray_is_unset(
146 struct xfarray *array,
147 loff_t pos)
148{
149 void *temp = xfarray_scratch(array);
150 int error;
151
152 if (array->unset_slots == 0)
153 return false;
154
155 error = xfile_obj_load(array->xfile, temp, array->obj_size, pos);
156 if (!error && xfarray_element_is_null(array, temp))
157 return true;
158
159 return false;
160}
161
162/*
163 * Unset an array element. If @idx is the last element in the array, the
164 * array will be truncated. Otherwise, the entry will be zeroed.
165 */
166int
167xfarray_unset(
168 struct xfarray *array,
169 xfarray_idx_t idx)
170{
171 void *temp = xfarray_scratch(array);
172 loff_t pos = xfarray_pos(array, idx);
173 int error;
174
175 if (idx >= array->nr)
176 return -ENODATA;
177
178 if (idx == array->nr - 1) {
179 array->nr--;
180 return 0;
181 }
182
183 if (xfarray_is_unset(array, pos))
184 return 0;
185
186 memset(temp, 0, array->obj_size);
187 error = xfile_obj_store(array->xfile, temp, array->obj_size, pos);
188 if (error)
189 return error;
190
191 array->unset_slots++;
192 return 0;
193}
194
195/*
196 * Store an element in the array. The element must not be completely zeroed,
197 * because those are considered unset sparse elements.
198 */
199int
200xfarray_store(
201 struct xfarray *array,
202 xfarray_idx_t idx,
203 const void *ptr)
204{
205 int ret;
206
207 if (idx >= array->max_nr)
208 return -EFBIG;
209
210 ASSERT(!xfarray_element_is_null(array, ptr));
211
212 ret = xfile_obj_store(array->xfile, ptr, array->obj_size,
213 xfarray_pos(array, idx));
214 if (ret)
215 return ret;
216
217 array->nr = max(array->nr, idx + 1);
218 return 0;
219}
220
221/* Is this array element NULL? */
222bool
223xfarray_element_is_null(
224 struct xfarray *array,
225 const void *ptr)
226{
227 return !memchr_inv(ptr, 0, array->obj_size);
228}
229
230/*
231 * Store an element anywhere in the array that is unset. If there are no
232 * unset slots, append the element to the array.
233 */
234int
235xfarray_store_anywhere(
236 struct xfarray *array,
237 const void *ptr)
238{
239 void *temp = xfarray_scratch(array);
240 loff_t endpos = xfarray_pos(array, array->nr);
241 loff_t pos;
242 int error;
243
244 /* Find an unset slot to put it in. */
245 for (pos = 0;
246 pos < endpos && array->unset_slots > 0;
247 pos += array->obj_size) {
248 error = xfile_obj_load(array->xfile, temp, array->obj_size,
249 pos);
250 if (error || !xfarray_element_is_null(array, temp))
251 continue;
252
253 error = xfile_obj_store(array->xfile, ptr, array->obj_size,
254 pos);
255 if (error)
256 return error;
257
258 array->unset_slots--;
259 return 0;
260 }
261
262 /* No unset slots found; attach it on the end. */
263 array->unset_slots = 0;
264 return xfarray_append(array, ptr);
265}
266
267/* Return length of array. */
268uint64_t
269xfarray_length(
270 struct xfarray *array)
271{
272 return array->nr;
273}
274
275/*
276 * Decide which array item we're going to read as part of an _iter_get.
277 * @cur is the array index, and @pos is the file offset of that array index in
278 * the backing xfile. Returns ENODATA if we reach the end of the records.
279 *
280 * Reading from a hole in a sparse xfile causes page instantiation, so for
281 * iterating a (possibly sparse) array we need to figure out if the cursor is
282 * pointing at a totally uninitialized hole and move the cursor up if
283 * necessary.
284 */
285static inline int
286xfarray_find_data(
287 struct xfarray *array,
288 xfarray_idx_t *cur,
289 loff_t *pos)
290{
291 unsigned int pgoff = offset_in_page(*pos);
292 loff_t end_pos = *pos + array->obj_size - 1;
293 loff_t new_pos;
294
295 /*
296 * If the current array record is not adjacent to a page boundary, we
297 * are in the middle of the page. We do not need to move the cursor.
298 */
299 if (pgoff != 0 && pgoff + array->obj_size - 1 < PAGE_SIZE)
300 return 0;
301
302 /*
303 * Call SEEK_DATA on the last byte in the record we're about to read.
304 * If the record ends at (or crosses) the end of a page then we know
305 * that the first byte of the record is backed by pages and don't need
306 * to query it. If instead the record begins at the start of the page
307 * then we know that querying the last byte is just as good as querying
308 * the first byte, since records cannot be larger than a page.
309 *
310 * If the call returns the same file offset, we know this record is
311 * backed by real pages. We do not need to move the cursor.
312 */
313 new_pos = xfile_seek_data(array->xfile, end_pos);
314 if (new_pos == -ENXIO)
315 return -ENODATA;
316 if (new_pos < 0)
317 return new_pos;
318 if (new_pos == end_pos)
319 return 0;
320
321 /*
322 * Otherwise, SEEK_DATA told us how far up to move the file pointer to
323 * find more data. Move the array index to the first record past the
324 * byte offset we were given.
325 */
326 new_pos = roundup_64(new_pos, array->obj_size);
327 *cur = xfarray_idx(array, new_pos);
328 *pos = xfarray_pos(array, *cur);
329 return 0;
330}
331
332/*
333 * Starting at *idx, fetch the next non-null array entry and advance the index
334 * to set up the next _load_next call. Returns ENODATA if we reach the end of
335 * the array. Callers must set @*idx to XFARRAY_CURSOR_INIT before the first
336 * call to this function.
337 */
338int
339xfarray_load_next(
340 struct xfarray *array,
341 xfarray_idx_t *idx,
342 void *rec)
343{
344 xfarray_idx_t cur = *idx;
345 loff_t pos = xfarray_pos(array, cur);
346 int error;
347
348 do {
349 if (cur >= array->nr)
350 return -ENODATA;
351
352 /*
353 * Ask the backing store for the location of next possible
354 * written record, then retrieve that record.
355 */
356 error = xfarray_find_data(array, &cur, &pos);
357 if (error)
358 return error;
359 error = xfarray_load(array, cur, rec);
360 if (error)
361 return error;
362
363 cur++;
364 pos += array->obj_size;
365 } while (xfarray_element_is_null(array, rec));
366
367 *idx = cur;
368 return 0;
369}
370
371/* Sorting functions */
372
373#ifdef DEBUG
374# define xfarray_sort_bump_loads(si) do { (si)->loads++; } while (0)
375# define xfarray_sort_bump_stores(si) do { (si)->stores++; } while (0)
376# define xfarray_sort_bump_compares(si) do { (si)->compares++; } while (0)
377# define xfarray_sort_bump_heapsorts(si) do { (si)->heapsorts++; } while (0)
378#else
379# define xfarray_sort_bump_loads(si)
380# define xfarray_sort_bump_stores(si)
381# define xfarray_sort_bump_compares(si)
382# define xfarray_sort_bump_heapsorts(si)
383#endif /* DEBUG */
384
385/* Load an array element for sorting. */
386static inline int
387xfarray_sort_load(
388 struct xfarray_sortinfo *si,
389 xfarray_idx_t idx,
390 void *ptr)
391{
392 xfarray_sort_bump_loads(si);
393 return xfarray_load(si->array, idx, ptr);
394}
395
396/* Store an array element for sorting. */
397static inline int
398xfarray_sort_store(
399 struct xfarray_sortinfo *si,
400 xfarray_idx_t idx,
401 void *ptr)
402{
403 xfarray_sort_bump_stores(si);
404 return xfarray_store(si->array, idx, ptr);
405}
406
407/* Compare an array element for sorting. */
408static inline int
409xfarray_sort_cmp(
410 struct xfarray_sortinfo *si,
411 const void *a,
412 const void *b)
413{
414 xfarray_sort_bump_compares(si);
415 return si->cmp_fn(a, b);
416}
417
418/* Return a pointer to the low index stack for quicksort partitioning. */
419static inline xfarray_idx_t *xfarray_sortinfo_lo(struct xfarray_sortinfo *si)
420{
421 return (xfarray_idx_t *)(si + 1);
422}
423
424/* Return a pointer to the high index stack for quicksort partitioning. */
425static inline xfarray_idx_t *xfarray_sortinfo_hi(struct xfarray_sortinfo *si)
426{
427 return xfarray_sortinfo_lo(si) + si->max_stack_depth;
428}
429
430/* Size of each element in the quicksort pivot array. */
431static inline size_t
432xfarray_pivot_rec_sz(
433 struct xfarray *array)
434{
435 return round_up(array->obj_size, 8) + sizeof(xfarray_idx_t);
436}
437
438/* Allocate memory to handle the sort. */
439static inline int
440xfarray_sortinfo_alloc(
441 struct xfarray *array,
442 xfarray_cmp_fn cmp_fn,
443 unsigned int flags,
444 struct xfarray_sortinfo **infop)
445{
446 struct xfarray_sortinfo *si;
447 size_t nr_bytes = sizeof(struct xfarray_sortinfo);
448 size_t pivot_rec_sz = xfarray_pivot_rec_sz(array);
449 int max_stack_depth;
450
451 /*
452 * The median-of-nine pivot algorithm doesn't work if a subset has
453 * fewer than 9 items. Make sure the in-memory sort will always take
454 * over for subsets where this wouldn't be the case.
455 */
456 BUILD_BUG_ON(XFARRAY_QSORT_PIVOT_NR >= XFARRAY_ISORT_NR);
457
458 /*
459 * Tail-call recursion during the partitioning phase means that
460 * quicksort will never recurse more than log2(nr) times. We need one
461 * extra level of stack to hold the initial parameters. In-memory
462 * sort will always take care of the last few levels of recursion for
463 * us, so we can reduce the stack depth by that much.
464 */
465 max_stack_depth = ilog2(array->nr) + 1 - (XFARRAY_ISORT_SHIFT - 1);
466 if (max_stack_depth < 1)
467 max_stack_depth = 1;
468
469 /* Each level of quicksort uses a lo and a hi index */
470 nr_bytes += max_stack_depth * sizeof(xfarray_idx_t) * 2;
471
472 /* Scratchpad for in-memory sort, or finding the pivot */
473 nr_bytes += max_t(size_t,
474 (XFARRAY_QSORT_PIVOT_NR + 1) * pivot_rec_sz,
475 XFARRAY_ISORT_NR * array->obj_size);
476
477 si = kvzalloc(nr_bytes, XCHK_GFP_FLAGS);
478 if (!si)
479 return -ENOMEM;
480
481 si->array = array;
482 si->cmp_fn = cmp_fn;
483 si->flags = flags;
484 si->max_stack_depth = max_stack_depth;
485 si->max_stack_used = 1;
486
487 xfarray_sortinfo_lo(si)[0] = 0;
488 xfarray_sortinfo_hi(si)[0] = array->nr - 1;
489
490 trace_xfarray_sort(si, nr_bytes);
491 *infop = si;
492 return 0;
493}
494
495/* Should this sort be terminated by a fatal signal? */
496static inline bool
497xfarray_sort_terminated(
498 struct xfarray_sortinfo *si,
499 int *error)
500{
501 /*
502 * If preemption is disabled, we need to yield to the scheduler every
503 * few seconds so that we don't run afoul of the soft lockup watchdog
504 * or RCU stall detector.
505 */
506 cond_resched();
507
508 if ((si->flags & XFARRAY_SORT_KILLABLE) &&
509 fatal_signal_pending(current)) {
510 if (*error == 0)
511 *error = -EINTR;
512 return true;
513 }
514 return false;
515}
516
517/* Do we want an in-memory sort? */
518static inline bool
519xfarray_want_isort(
520 struct xfarray_sortinfo *si,
521 xfarray_idx_t start,
522 xfarray_idx_t end)
523{
524 /*
525 * For array subsets that fit in the scratchpad, it's much faster to
526 * use the kernel's heapsort than quicksort's stack machine.
527 */
528 return (end - start) < XFARRAY_ISORT_NR;
529}
530
531/* Return the scratch space within the sortinfo structure. */
532static inline void *xfarray_sortinfo_isort_scratch(struct xfarray_sortinfo *si)
533{
534 return xfarray_sortinfo_hi(si) + si->max_stack_depth;
535}
536
537/*
538 * Sort a small number of array records using scratchpad memory. The records
539 * need not be contiguous in the xfile's memory pages.
540 */
541STATIC int
542xfarray_isort(
543 struct xfarray_sortinfo *si,
544 xfarray_idx_t lo,
545 xfarray_idx_t hi)
546{
547 void *scratch = xfarray_sortinfo_isort_scratch(si);
548 loff_t lo_pos = xfarray_pos(si->array, lo);
549 loff_t len = xfarray_pos(si->array, hi - lo + 1);
550 int error;
551
552 trace_xfarray_isort(si, lo, hi);
553
554 xfarray_sort_bump_loads(si);
555 error = xfile_obj_load(si->array->xfile, scratch, len, lo_pos);
556 if (error)
557 return error;
558
559 xfarray_sort_bump_heapsorts(si);
560 sort(scratch, hi - lo + 1, si->array->obj_size, si->cmp_fn, NULL);
561
562 xfarray_sort_bump_stores(si);
563 return xfile_obj_store(si->array->xfile, scratch, len, lo_pos);
564}
565
566/* Grab a page for sorting records. */
567static inline int
568xfarray_sort_get_page(
569 struct xfarray_sortinfo *si,
570 loff_t pos,
571 uint64_t len)
572{
573 int error;
574
575 error = xfile_get_page(si->array->xfile, pos, len, &si->xfpage);
576 if (error)
577 return error;
578
579 /*
580 * xfile pages must never be mapped into userspace, so we skip the
581 * dcache flush when mapping the page.
582 */
583 si->page_kaddr = kmap_local_page(si->xfpage.page);
584 return 0;
585}
586
587/* Release a page we grabbed for sorting records. */
588static inline int
589xfarray_sort_put_page(
590 struct xfarray_sortinfo *si)
591{
592 if (!si->page_kaddr)
593 return 0;
594
595 kunmap_local(si->page_kaddr);
596 si->page_kaddr = NULL;
597
598 return xfile_put_page(si->array->xfile, &si->xfpage);
599}
600
601/* Decide if these records are eligible for in-page sorting. */
602static inline bool
603xfarray_want_pagesort(
604 struct xfarray_sortinfo *si,
605 xfarray_idx_t lo,
606 xfarray_idx_t hi)
607{
608 pgoff_t lo_page;
609 pgoff_t hi_page;
610 loff_t end_pos;
611
612 /* We can only map one page at a time. */
613 lo_page = xfarray_pos(si->array, lo) >> PAGE_SHIFT;
614 end_pos = xfarray_pos(si->array, hi) + si->array->obj_size - 1;
615 hi_page = end_pos >> PAGE_SHIFT;
616
617 return lo_page == hi_page;
618}
619
620/* Sort a bunch of records that all live in the same memory page. */
621STATIC int
622xfarray_pagesort(
623 struct xfarray_sortinfo *si,
624 xfarray_idx_t lo,
625 xfarray_idx_t hi)
626{
627 void *startp;
628 loff_t lo_pos = xfarray_pos(si->array, lo);
629 uint64_t len = xfarray_pos(si->array, hi - lo);
630 int error = 0;
631
632 trace_xfarray_pagesort(si, lo, hi);
633
634 xfarray_sort_bump_loads(si);
635 error = xfarray_sort_get_page(si, lo_pos, len);
636 if (error)
637 return error;
638
639 xfarray_sort_bump_heapsorts(si);
640 startp = si->page_kaddr + offset_in_page(lo_pos);
641 sort(startp, hi - lo + 1, si->array->obj_size, si->cmp_fn, NULL);
642
643 xfarray_sort_bump_stores(si);
644 return xfarray_sort_put_page(si);
645}
646
647/* Return a pointer to the xfarray pivot record within the sortinfo struct. */
648static inline void *xfarray_sortinfo_pivot(struct xfarray_sortinfo *si)
649{
650 return xfarray_sortinfo_hi(si) + si->max_stack_depth;
651}
652
653/* Return a pointer to the start of the pivot array. */
654static inline void *
655xfarray_sortinfo_pivot_array(
656 struct xfarray_sortinfo *si)
657{
658 return xfarray_sortinfo_pivot(si) + si->array->obj_size;
659}
660
661/* The xfarray record is stored at the start of each pivot array element. */
662static inline void *
663xfarray_pivot_array_rec(
664 void *pa,
665 size_t pa_recsz,
666 unsigned int pa_idx)
667{
668 return pa + (pa_recsz * pa_idx);
669}
670
671/* The xfarray index is stored at the end of each pivot array element. */
672static inline xfarray_idx_t *
673xfarray_pivot_array_idx(
674 void *pa,
675 size_t pa_recsz,
676 unsigned int pa_idx)
677{
678 return xfarray_pivot_array_rec(pa, pa_recsz, pa_idx + 1) -
679 sizeof(xfarray_idx_t);
680}
681
682/*
683 * Find a pivot value for quicksort partitioning, swap it with a[lo], and save
684 * the cached pivot record for the next step.
685 *
686 * Load evenly-spaced records within the given range into memory, sort them,
687 * and choose the pivot from the median record. Using multiple points will
688 * improve the quality of the pivot selection, and hopefully avoid the worst
689 * quicksort behavior, since our array values are nearly always evenly sorted.
690 */
691STATIC int
692xfarray_qsort_pivot(
693 struct xfarray_sortinfo *si,
694 xfarray_idx_t lo,
695 xfarray_idx_t hi)
696{
697 void *pivot = xfarray_sortinfo_pivot(si);
698 void *parray = xfarray_sortinfo_pivot_array(si);
699 void *recp;
700 xfarray_idx_t *idxp;
701 xfarray_idx_t step = (hi - lo) / (XFARRAY_QSORT_PIVOT_NR - 1);
702 size_t pivot_rec_sz = xfarray_pivot_rec_sz(si->array);
703 int i, j;
704 int error;
705
706 ASSERT(step > 0);
707
708 /*
709 * Load the xfarray indexes of the records we intend to sample into the
710 * pivot array.
711 */
712 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz, 0);
713 *idxp = lo;
714 for (i = 1; i < XFARRAY_QSORT_PIVOT_NR - 1; i++) {
715 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz, i);
716 *idxp = lo + (i * step);
717 }
718 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz,
719 XFARRAY_QSORT_PIVOT_NR - 1);
720 *idxp = hi;
721
722 /* Load the selected xfarray records into the pivot array. */
723 for (i = 0; i < XFARRAY_QSORT_PIVOT_NR; i++) {
724 xfarray_idx_t idx;
725
726 recp = xfarray_pivot_array_rec(parray, pivot_rec_sz, i);
727 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz, i);
728
729 /* No unset records; load directly into the array. */
730 if (likely(si->array->unset_slots == 0)) {
731 error = xfarray_sort_load(si, *idxp, recp);
732 if (error)
733 return error;
734 continue;
735 }
736
737 /*
738 * Load non-null records into the scratchpad without changing
739 * the xfarray_idx_t in the pivot array.
740 */
741 idx = *idxp;
742 xfarray_sort_bump_loads(si);
743 error = xfarray_load_next(si->array, &idx, recp);
744 if (error)
745 return error;
746 }
747
748 xfarray_sort_bump_heapsorts(si);
749 sort(parray, XFARRAY_QSORT_PIVOT_NR, pivot_rec_sz, si->cmp_fn, NULL);
750
751 /*
752 * We sorted the pivot array records (which includes the xfarray
753 * indices) in xfarray record order. The median element of the pivot
754 * array contains the xfarray record that we will use as the pivot.
755 * Copy that xfarray record to the designated space.
756 */
757 recp = xfarray_pivot_array_rec(parray, pivot_rec_sz,
758 XFARRAY_QSORT_PIVOT_NR / 2);
759 memcpy(pivot, recp, si->array->obj_size);
760
761 /* If the pivot record we chose was already in a[lo] then we're done. */
762 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz,
763 XFARRAY_QSORT_PIVOT_NR / 2);
764 if (*idxp == lo)
765 return 0;
766
767 /*
768 * Find the cached copy of a[lo] in the pivot array so that we can swap
769 * a[lo] and a[pivot].
770 */
771 for (i = 0, j = -1; i < XFARRAY_QSORT_PIVOT_NR; i++) {
772 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz, i);
773 if (*idxp == lo)
774 j = i;
775 }
776 if (j < 0) {
777 ASSERT(j >= 0);
778 return -EFSCORRUPTED;
779 }
780
781 /* Swap a[lo] and a[pivot]. */
782 error = xfarray_sort_store(si, lo, pivot);
783 if (error)
784 return error;
785
786 recp = xfarray_pivot_array_rec(parray, pivot_rec_sz, j);
787 idxp = xfarray_pivot_array_idx(parray, pivot_rec_sz,
788 XFARRAY_QSORT_PIVOT_NR / 2);
789 return xfarray_sort_store(si, *idxp, recp);
790}
791
792/*
793 * Set up the pointers for the next iteration. We push onto the stack all of
794 * the unsorted values between a[lo + 1] and a[end[i]], and we tweak the
795 * current stack frame to point to the unsorted values between a[beg[i]] and
796 * a[lo] so that those values will be sorted when we pop the stack.
797 */
798static inline int
799xfarray_qsort_push(
800 struct xfarray_sortinfo *si,
801 xfarray_idx_t *si_lo,
802 xfarray_idx_t *si_hi,
803 xfarray_idx_t lo,
804 xfarray_idx_t hi)
805{
806 /* Check for stack overflows */
807 if (si->stack_depth >= si->max_stack_depth - 1) {
808 ASSERT(si->stack_depth < si->max_stack_depth - 1);
809 return -EFSCORRUPTED;
810 }
811
812 si->max_stack_used = max_t(uint8_t, si->max_stack_used,
813 si->stack_depth + 2);
814
815 si_lo[si->stack_depth + 1] = lo + 1;
816 si_hi[si->stack_depth + 1] = si_hi[si->stack_depth];
817 si_hi[si->stack_depth++] = lo - 1;
818
819 /*
820 * Always start with the smaller of the two partitions to keep the
821 * amount of recursion in check.
822 */
823 if (si_hi[si->stack_depth] - si_lo[si->stack_depth] >
824 si_hi[si->stack_depth - 1] - si_lo[si->stack_depth - 1]) {
825 swap(si_lo[si->stack_depth], si_lo[si->stack_depth - 1]);
826 swap(si_hi[si->stack_depth], si_hi[si->stack_depth - 1]);
827 }
828
829 return 0;
830}
831
832/*
833 * Load an element from the array into the first scratchpad and cache the page,
834 * if possible.
835 */
836static inline int
837xfarray_sort_load_cached(
838 struct xfarray_sortinfo *si,
839 xfarray_idx_t idx,
840 void *ptr)
841{
842 loff_t idx_pos = xfarray_pos(si->array, idx);
843 pgoff_t startpage;
844 pgoff_t endpage;
845 int error = 0;
846
847 /*
848 * If this load would split a page, release the cached page, if any,
849 * and perform a traditional read.
850 */
851 startpage = idx_pos >> PAGE_SHIFT;
852 endpage = (idx_pos + si->array->obj_size - 1) >> PAGE_SHIFT;
853 if (startpage != endpage) {
854 error = xfarray_sort_put_page(si);
855 if (error)
856 return error;
857
858 if (xfarray_sort_terminated(si, &error))
859 return error;
860
861 return xfile_obj_load(si->array->xfile, ptr,
862 si->array->obj_size, idx_pos);
863 }
864
865 /* If the cached page is not the one we want, release it. */
866 if (xfile_page_cached(&si->xfpage) &&
867 xfile_page_index(&si->xfpage) != startpage) {
868 error = xfarray_sort_put_page(si);
869 if (error)
870 return error;
871 }
872
873 /*
874 * If we don't have a cached page (and we know the load is contained
875 * in a single page) then grab it.
876 */
877 if (!xfile_page_cached(&si->xfpage)) {
878 if (xfarray_sort_terminated(si, &error))
879 return error;
880
881 error = xfarray_sort_get_page(si, startpage << PAGE_SHIFT,
882 PAGE_SIZE);
883 if (error)
884 return error;
885 }
886
887 memcpy(ptr, si->page_kaddr + offset_in_page(idx_pos),
888 si->array->obj_size);
889 return 0;
890}
891
892/*
893 * Sort the array elements via quicksort. This implementation incorporates
894 * four optimizations discussed in Sedgewick:
895 *
896 * 1. Use an explicit stack of array indices to store the next array partition
897 * to sort. This helps us to avoid recursion in the call stack, which is
898 * particularly expensive in the kernel.
899 *
900 * 2. For arrays with records in arbitrary or user-controlled order, choose the
901 * pivot element using a median-of-nine decision tree. This reduces the
902 * probability of selecting a bad pivot value which causes worst case
903 * behavior (i.e. partition sizes of 1).
904 *
905 * 3. The smaller of the two sub-partitions is pushed onto the stack to start
906 * the next level of recursion, and the larger sub-partition replaces the
907 * current stack frame. This guarantees that we won't need more than
908 * log2(nr) stack space.
909 *
910 * 4. For small sets, load the records into the scratchpad and run heapsort on
911 * them because that is very fast. In the author's experience, this yields
912 * a ~10% reduction in runtime.
913 *
914 * If a small set is contained entirely within a single xfile memory page,
915 * map the page directly and run heap sort directly on the xfile page
916 * instead of using the load/store interface. This halves the runtime.
917 *
918 * 5. This optimization is specific to the implementation. When converging lo
919 * and hi after selecting a pivot, we will try to retain the xfile memory
920 * page between load calls, which reduces run time by 50%.
921 */
922
923/*
924 * Due to the use of signed indices, we can only support up to 2^63 records.
925 * Files can only grow to 2^63 bytes, so this is not much of a limitation.
926 */
927#define QSORT_MAX_RECS (1ULL << 63)
928
929int
930xfarray_sort(
931 struct xfarray *array,
932 xfarray_cmp_fn cmp_fn,
933 unsigned int flags)
934{
935 struct xfarray_sortinfo *si;
936 xfarray_idx_t *si_lo, *si_hi;
937 void *pivot;
938 void *scratch = xfarray_scratch(array);
939 xfarray_idx_t lo, hi;
940 int error = 0;
941
942 if (array->nr < 2)
943 return 0;
944 if (array->nr >= QSORT_MAX_RECS)
945 return -E2BIG;
946
947 error = xfarray_sortinfo_alloc(array, cmp_fn, flags, &si);
948 if (error)
949 return error;
950 si_lo = xfarray_sortinfo_lo(si);
951 si_hi = xfarray_sortinfo_hi(si);
952 pivot = xfarray_sortinfo_pivot(si);
953
954 while (si->stack_depth >= 0) {
955 lo = si_lo[si->stack_depth];
956 hi = si_hi[si->stack_depth];
957
958 trace_xfarray_qsort(si, lo, hi);
959
960 /* Nothing left in this partition to sort; pop stack. */
961 if (lo >= hi) {
962 si->stack_depth--;
963 continue;
964 }
965
966 /*
967 * If directly mapping the page and sorting can solve our
968 * problems, we're done.
969 */
970 if (xfarray_want_pagesort(si, lo, hi)) {
971 error = xfarray_pagesort(si, lo, hi);
972 if (error)
973 goto out_free;
974 si->stack_depth--;
975 continue;
976 }
977
978 /* If insertion sort can solve our problems, we're done. */
979 if (xfarray_want_isort(si, lo, hi)) {
980 error = xfarray_isort(si, lo, hi);
981 if (error)
982 goto out_free;
983 si->stack_depth--;
984 continue;
985 }
986
987 /* Pick a pivot, move it to a[lo] and stash it. */
988 error = xfarray_qsort_pivot(si, lo, hi);
989 if (error)
990 goto out_free;
991
992 /*
993 * Rearrange a[lo..hi] such that everything smaller than the
994 * pivot is on the left side of the range and everything larger
995 * than the pivot is on the right side of the range.
996 */
997 while (lo < hi) {
998 /*
999 * Decrement hi until it finds an a[hi] less than the
1000 * pivot value.
1001 */
1002 error = xfarray_sort_load_cached(si, hi, scratch);
1003 if (error)
1004 goto out_free;
1005 while (xfarray_sort_cmp(si, scratch, pivot) >= 0 &&
1006 lo < hi) {
1007 hi--;
1008 error = xfarray_sort_load_cached(si, hi,
1009 scratch);
1010 if (error)
1011 goto out_free;
1012 }
1013 error = xfarray_sort_put_page(si);
1014 if (error)
1015 goto out_free;
1016
1017 if (xfarray_sort_terminated(si, &error))
1018 goto out_free;
1019
1020 /* Copy that item (a[hi]) to a[lo]. */
1021 if (lo < hi) {
1022 error = xfarray_sort_store(si, lo++, scratch);
1023 if (error)
1024 goto out_free;
1025 }
1026
1027 /*
1028 * Increment lo until it finds an a[lo] greater than
1029 * the pivot value.
1030 */
1031 error = xfarray_sort_load_cached(si, lo, scratch);
1032 if (error)
1033 goto out_free;
1034 while (xfarray_sort_cmp(si, scratch, pivot) <= 0 &&
1035 lo < hi) {
1036 lo++;
1037 error = xfarray_sort_load_cached(si, lo,
1038 scratch);
1039 if (error)
1040 goto out_free;
1041 }
1042 error = xfarray_sort_put_page(si);
1043 if (error)
1044 goto out_free;
1045
1046 if (xfarray_sort_terminated(si, &error))
1047 goto out_free;
1048
1049 /* Copy that item (a[lo]) to a[hi]. */
1050 if (lo < hi) {
1051 error = xfarray_sort_store(si, hi--, scratch);
1052 if (error)
1053 goto out_free;
1054 }
1055
1056 if (xfarray_sort_terminated(si, &error))
1057 goto out_free;
1058 }
1059
1060 /*
1061 * Put our pivot value in the correct place at a[lo]. All
1062 * values between a[beg[i]] and a[lo - 1] should be less than
1063 * the pivot; and all values between a[lo + 1] and a[end[i]-1]
1064 * should be greater than the pivot.
1065 */
1066 error = xfarray_sort_store(si, lo, pivot);
1067 if (error)
1068 goto out_free;
1069
1070 /* Set up the stack frame to process the two partitions. */
1071 error = xfarray_qsort_push(si, si_lo, si_hi, lo, hi);
1072 if (error)
1073 goto out_free;
1074
1075 if (xfarray_sort_terminated(si, &error))
1076 goto out_free;
1077 }
1078
1079out_free:
1080 trace_xfarray_sort_stats(si, error);
1081 kvfree(si);
1082 return error;
1083}