2 * BLIST.C - Bitmap allocator/deallocator, using a radix tree with hinting
4 * Copyright (c) 1998,2004 The DragonFly Project. All rights reserved.
6 * This code is derived from software contributed to The DragonFly Project
7 * by Matthew Dillon <dillon@backplane.com>
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in
17 * the documentation and/or other materials provided with the
19 * 3. Neither the name of The DragonFly Project nor the names of its
20 * contributors may be used to endorse or promote products derived
21 * from this software without specific, prior written permission.
23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
24 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
26 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
27 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
28 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
29 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
30 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
31 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
32 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * This module implements a general bitmap allocator/deallocator. The
38 * allocator eats around 2 bits per 'block'. The module does not
39 * try to interpret the meaning of a 'block' other then to return
40 * SWAPBLK_NONE on an allocation failure.
42 * A radix tree is used to maintain the bitmap. Two radix constants are
43 * involved: One for the bitmaps contained in the leaf nodes (typically
44 * 32), and one for the meta nodes (typically 16). Both meta and leaf
45 * nodes have a hint field. This field gives us a hint as to the largest
46 * free contiguous range of blocks under the node. It may contain a
47 * value that is too high, but will never contain a value that is too
48 * low. When the radix tree is searched, allocation failures in subtrees
51 * The radix tree also implements two collapsed states for meta nodes:
52 * the ALL-ALLOCATED state and the ALL-FREE state. If a meta node is
53 * in either of these two states, all information contained underneath
54 * the node is considered stale. These states are used to optimize
55 * allocation and freeing operations.
57 * The hinting greatly increases code efficiency for allocations while
58 * the general radix structure optimizes both allocations and frees. The
59 * radix tree should be able to operate well no matter how much
60 * fragmentation there is and no matter how large a bitmap is used.
62 * Unlike the rlist code, the blist code wires all necessary memory at
63 * creation time. Neither allocations nor frees require interaction with
64 * the memory subsystem. In contrast, the rlist code may allocate memory
65 * on an rlist_free() call. The non-blocking features of the blist code
66 * are used to great advantage in the swap code (vm/nswap_pager.c). The
67 * rlist code uses a little less overall memory then the blist code (but
68 * due to swap interleaving not all that much less), but the blist code
69 * scales much, much better.
71 * LAYOUT: The radix tree is layed out recursively using a
72 * linear array. Each meta node is immediately followed (layed out
73 * sequentially in memory) by BLIST_META_RADIX lower level nodes. This
74 * is a recursive structure but one that can be easily scanned through
75 * a very simple 'skip' calculation. In order to support large radixes,
76 * portions of the tree may reside outside our memory allocation. We
77 * handle this with an early-termination optimization (when bighint is
78 * set to -1) on the scan. The memory allocation is only large enough
79 * to cover the number of blocks requested at creation time even if it
80 * must be encompassed in larger root-node radix.
82 * NOTE: The allocator cannot currently allocate more then
83 * BLIST_BMAP_RADIX blocks per call. It will panic with 'allocation too
84 * large' if you try. This is an area that could use improvement. The
85 * radix is large enough that this restriction does not effect the swap
86 * system, though. Currently only the allocation code is effected by
87 * this algorithmic unfeature. The freeing code can handle arbitrary
90 * NOTE: The radix may exceed 32 bits in order to support up to 2^31
91 * blocks. The first divison will drop the radix down and fit
92 * it within a signed 32 bit integer.
94 * This code can be compiled stand-alone for debugging.
96 * $FreeBSD: src/sys/kern/subr_blist.c,v 1.5.2.2 2003/01/12 09:23:12 dillon Exp $
97 * $DragonFly: src/sys/kern/subr_blist.c,v 1.8 2008/08/10 22:09:50 dillon Exp $
102 #include <sys/param.h>
103 #include <sys/systm.h>
104 #include <sys/lock.h>
105 #include <sys/kernel.h>
106 #include <sys/blist.h>
107 #include <sys/malloc.h>
111 #ifndef BLIST_NO_DEBUG
115 #define SWAPBLK_NONE ((swblk_t)-1)
117 #include <sys/types.h>
123 #define kmalloc(a,b,c) malloc(a)
124 #define kfree(a,b) free(a)
125 #define kprintf printf
126 #define KKASSERT(exp)
128 #include <sys/blist.h>
130 void panic(const char *ctl, ...);
135 * static support functions
138 static swblk_t blst_leaf_alloc(blmeta_t *scan, swblk_t blk, int count);
139 static swblk_t blst_meta_alloc(blmeta_t *scan, swblk_t blk,
140 swblk_t count, int64_t radix, int skip);
141 static void blst_leaf_free(blmeta_t *scan, swblk_t relblk, int count);
142 static void blst_meta_free(blmeta_t *scan, swblk_t freeBlk, swblk_t count,
143 int64_t radix, int skip, swblk_t blk);
144 static void blst_copy(blmeta_t *scan, swblk_t blk, int64_t radix,
145 swblk_t skip, blist_t dest, swblk_t count);
146 static swblk_t blst_radix_init(blmeta_t *scan, int64_t radix,
147 int skip, swblk_t count);
149 static void blst_radix_print(blmeta_t *scan, swblk_t blk,
150 int64_t radix, int skip, int tab);
154 static MALLOC_DEFINE(M_SWAP, "SWAP", "Swap space");
158 * blist_create() - create a blist capable of handling up to the specified
161 * blocks must be greater then 0
163 * The smallest blist consists of a single leaf node capable of
164 * managing BLIST_BMAP_RADIX blocks.
168 blist_create(swblk_t blocks)
175 * Calculate radix and skip field used for scanning.
177 * Radix can exceed 32 bits even if swblk_t is limited to 32 bits.
179 radix = BLIST_BMAP_RADIX;
181 while (radix < blocks) {
182 radix *= BLIST_META_RADIX;
183 skip = (skip + 1) * BLIST_META_RADIX;
187 bl = kmalloc(sizeof(struct blist), M_SWAP, M_WAITOK);
189 bzero(bl, sizeof(*bl));
191 bl->bl_blocks = blocks;
192 bl->bl_radix = radix;
194 bl->bl_rootblks = 1 +
195 blst_radix_init(NULL, bl->bl_radix, bl->bl_skip, blocks);
196 bl->bl_root = kmalloc(sizeof(blmeta_t) * bl->bl_rootblks, M_SWAP, M_WAITOK);
198 #if defined(BLIST_DEBUG)
200 "BLIST representing %d blocks (%d MB of swap)"
201 ", requiring %dK of ram\n",
203 bl->bl_blocks * 4 / 1024,
204 (bl->bl_rootblks * sizeof(blmeta_t) + 1023) / 1024
206 kprintf("BLIST raw radix tree contains %d records\n", bl->bl_rootblks);
208 blst_radix_init(bl->bl_root, bl->bl_radix, bl->bl_skip, blocks);
214 blist_destroy(blist_t bl)
216 kfree(bl->bl_root, M_SWAP);
221 * blist_alloc() - reserve space in the block bitmap. Return the base
222 * of a contiguous region or SWAPBLK_NONE if space could
227 blist_alloc(blist_t bl, swblk_t count)
229 swblk_t blk = SWAPBLK_NONE;
232 if (bl->bl_radix == BLIST_BMAP_RADIX)
233 blk = blst_leaf_alloc(bl->bl_root, 0, count);
235 blk = blst_meta_alloc(bl->bl_root, 0, count, bl->bl_radix, bl->bl_skip);
236 if (blk != SWAPBLK_NONE)
237 bl->bl_free -= count;
243 * blist_free() - free up space in the block bitmap. Return the base
244 * of a contiguous region. Panic if an inconsistancy is
249 blist_free(blist_t bl, swblk_t blkno, swblk_t count)
252 if (bl->bl_radix == BLIST_BMAP_RADIX)
253 blst_leaf_free(bl->bl_root, blkno, count);
255 blst_meta_free(bl->bl_root, blkno, count, bl->bl_radix, bl->bl_skip, 0);
256 bl->bl_free += count;
261 * blist_resize() - resize an existing radix tree to handle the
262 * specified number of blocks. This will reallocate
263 * the tree and transfer the previous bitmap to the new
264 * one. When extending the tree you can specify whether
265 * the new blocks are to left allocated or freed.
269 blist_resize(blist_t *pbl, swblk_t count, int freenew)
271 blist_t newbl = blist_create(count);
275 if (count > save->bl_blocks)
276 count = save->bl_blocks;
277 blst_copy(save->bl_root, 0, save->bl_radix, save->bl_skip, newbl, count);
280 * If resizing upwards, should we free the new space or not?
282 if (freenew && count < newbl->bl_blocks) {
283 blist_free(newbl, count, newbl->bl_blocks - count);
291 * blist_print() - dump radix tree
295 blist_print(blist_t bl)
297 kprintf("BLIST {\n");
298 blst_radix_print(bl->bl_root, 0, bl->bl_radix, bl->bl_skip, 4);
304 /************************************************************************
305 * ALLOCATION SUPPORT FUNCTIONS *
306 ************************************************************************
308 * These support functions do all the actual work. They may seem
309 * rather longish, but that's because I've commented them up. The
310 * actual code is straight forward.
315 * blist_leaf_alloc() - allocate at a leaf in the radix tree (a bitmap).
317 * This is the core of the allocator and is optimized for the 1 block
318 * and the BLIST_BMAP_RADIX block allocation cases. Other cases are
319 * somewhat slower. The 1 block allocation case is log2 and extremely
324 blst_leaf_alloc(blmeta_t *scan, swblk_t blk, int count)
326 u_swblk_t orig = scan->u.bmu_bitmap;
330 * Optimize bitmap all-allocated case. Also, count = 1
331 * case assumes at least 1 bit is free in the bitmap, so
332 * we have to take care of this case here.
334 scan->bm_bighint = 0;
335 return(SWAPBLK_NONE);
339 * Optimized code to allocate one bit out of the bitmap
342 int j = BLIST_BMAP_RADIX/2;
345 mask = (u_swblk_t)-1 >> (BLIST_BMAP_RADIX/2);
348 if ((orig & mask) == 0) {
355 scan->u.bmu_bitmap &= ~(1 << r);
358 if (count <= BLIST_BMAP_RADIX) {
360 * non-optimized code to allocate N bits out of the bitmap.
361 * The more bits, the faster the code runs. It will run
362 * the slowest allocating 2 bits, but since there aren't any
363 * memory ops in the core loop (or shouldn't be, anyway),
364 * you probably won't notice the difference.
367 int n = BLIST_BMAP_RADIX - count;
370 mask = (u_swblk_t)-1 >> n;
372 for (j = 0; j <= n; ++j) {
373 if ((orig & mask) == mask) {
374 scan->u.bmu_bitmap &= ~mask;
381 * We couldn't allocate count in this subtree, update bighint.
383 scan->bm_bighint = count - 1;
384 return(SWAPBLK_NONE);
388 * blist_meta_alloc() - allocate at a meta in the radix tree.
390 * Attempt to allocate at a meta node. If we can't, we update
391 * bighint and return a failure. Updating bighint optimize future
392 * calls that hit this node. We have to check for our collapse cases
393 * and we have a few optimizations strewn in as well.
397 blst_meta_alloc(blmeta_t *scan, swblk_t blk, swblk_t count,
398 int64_t radix, int skip)
401 int next_skip = ((u_int)skip / BLIST_META_RADIX);
403 if (scan->u.bmu_avail == 0) {
405 * ALL-ALLOCATED special case
407 scan->bm_bighint = count;
408 return(SWAPBLK_NONE);
412 * note: radix may exceed 32 bits until first division.
414 if (scan->u.bmu_avail == radix) {
415 radix /= BLIST_META_RADIX;
418 * ALL-FREE special case, initialize uninitialize
421 for (i = 1; i <= skip; i += next_skip) {
422 if (scan[i].bm_bighint == (swblk_t)-1)
424 if (next_skip == 1) {
425 scan[i].u.bmu_bitmap = (u_swblk_t)-1;
426 scan[i].bm_bighint = BLIST_BMAP_RADIX;
428 scan[i].bm_bighint = (swblk_t)radix;
429 scan[i].u.bmu_avail = (swblk_t)radix;
433 radix /= BLIST_META_RADIX;
436 for (i = 1; i <= skip; i += next_skip) {
437 if (count <= scan[i].bm_bighint) {
439 * count fits in object
442 if (next_skip == 1) {
443 r = blst_leaf_alloc(&scan[i], blk, count);
445 r = blst_meta_alloc(&scan[i], blk, count, radix, next_skip - 1);
447 if (r != SWAPBLK_NONE) {
448 scan->u.bmu_avail -= count;
449 if (scan->bm_bighint > scan->u.bmu_avail)
450 scan->bm_bighint = scan->u.bmu_avail;
453 } else if (scan[i].bm_bighint == (swblk_t)-1) {
458 } else if (count > (swblk_t)radix) {
460 * count does not fit in object even if it were
463 panic("blist_meta_alloc: allocation too large");
465 blk += (swblk_t)radix;
469 * We couldn't allocate count in this subtree, update bighint.
471 if (scan->bm_bighint >= count)
472 scan->bm_bighint = count - 1;
473 return(SWAPBLK_NONE);
477 * BLST_LEAF_FREE() - free allocated block from leaf bitmap
482 blst_leaf_free(blmeta_t *scan, swblk_t blk, int count)
485 * free some data in this bitmap
488 * 0000111111111110000
492 int n = blk & (BLIST_BMAP_RADIX - 1);
495 mask = ((u_swblk_t)-1 << n) &
496 ((u_swblk_t)-1 >> (BLIST_BMAP_RADIX - count - n));
498 if (scan->u.bmu_bitmap & mask)
499 panic("blst_radix_free: freeing free block");
500 scan->u.bmu_bitmap |= mask;
503 * We could probably do a better job here. We are required to make
504 * bighint at least as large as the biggest contiguous block of
505 * data. If we just shoehorn it, a little extra overhead will
506 * be incured on the next allocation (but only that one typically).
508 scan->bm_bighint = BLIST_BMAP_RADIX;
512 * BLST_META_FREE() - free allocated blocks from radix tree meta info
514 * This support routine frees a range of blocks from the bitmap.
515 * The range must be entirely enclosed by this radix node. If a
516 * meta node, we break the range down recursively to free blocks
517 * in subnodes (which means that this code can free an arbitrary
518 * range whereas the allocation code cannot allocate an arbitrary
523 blst_meta_free(blmeta_t *scan, swblk_t freeBlk, swblk_t count,
524 int64_t radix, int skip, swblk_t blk)
527 int next_skip = ((u_int)skip / BLIST_META_RADIX);
530 kprintf("FREE (%x,%d) FROM (%x,%lld)\n",
532 blk, (long long)radix
537 * NOTE: radix may exceed 32 bits until first division.
539 if (scan->u.bmu_avail == 0) {
541 * ALL-ALLOCATED special case, with possible
542 * shortcut to ALL-FREE special case.
544 scan->u.bmu_avail = count;
545 scan->bm_bighint = count;
547 if (count != radix) {
548 for (i = 1; i <= skip; i += next_skip) {
549 if (scan[i].bm_bighint == (swblk_t)-1)
551 scan[i].bm_bighint = 0;
552 if (next_skip == 1) {
553 scan[i].u.bmu_bitmap = 0;
555 scan[i].u.bmu_avail = 0;
561 scan->u.bmu_avail += count;
562 /* scan->bm_bighint = radix; */
566 * ALL-FREE special case.
569 if (scan->u.bmu_avail == radix)
571 if (scan->u.bmu_avail > radix)
572 panic("blst_meta_free: freeing already free blocks (%d) %d/%lld", count, scan->u.bmu_avail, (long long)radix);
575 * Break the free down into its components
578 radix /= BLIST_META_RADIX;
580 i = (freeBlk - blk) / (swblk_t)radix;
581 blk += i * (swblk_t)radix;
582 i = i * next_skip + 1;
584 while (i <= skip && blk < freeBlk + count) {
587 v = blk + (swblk_t)radix - freeBlk;
591 if (scan->bm_bighint == (swblk_t)-1)
592 panic("blst_meta_free: freeing unexpected range");
594 if (next_skip == 1) {
595 blst_leaf_free(&scan[i], freeBlk, v);
597 blst_meta_free(&scan[i], freeBlk, v, radix, next_skip - 1, blk);
599 if (scan->bm_bighint < scan[i].bm_bighint)
600 scan->bm_bighint = scan[i].bm_bighint;
603 blk += (swblk_t)radix;
609 * BLIST_RADIX_COPY() - copy one radix tree to another
611 * Locates free space in the source tree and frees it in the destination
612 * tree. The space may not already be free in the destination.
616 blst_copy(blmeta_t *scan, swblk_t blk, int64_t radix,
617 swblk_t skip, blist_t dest, swblk_t count)
626 if (radix == BLIST_BMAP_RADIX) {
627 u_swblk_t v = scan->u.bmu_bitmap;
629 if (v == (u_swblk_t)-1) {
630 blist_free(dest, blk, count);
634 for (i = 0; i < BLIST_BMAP_RADIX && i < count; ++i) {
636 blist_free(dest, blk + i, 1);
646 if (scan->u.bmu_avail == 0) {
648 * Source all allocated, leave dest allocated
652 if (scan->u.bmu_avail == radix) {
654 * Source all free, free entire dest
657 blist_free(dest, blk, count);
659 blist_free(dest, blk, (swblk_t)radix);
664 radix /= BLIST_META_RADIX;
665 next_skip = ((u_int)skip / BLIST_META_RADIX);
667 for (i = 1; count && i <= skip; i += next_skip) {
668 if (scan[i].bm_bighint == (swblk_t)-1)
671 if (count >= (swblk_t)radix) {
680 count -= (swblk_t)radix;
694 blk += (swblk_t)radix;
699 * BLST_RADIX_INIT() - initialize radix tree
701 * Initialize our meta structures and bitmaps and calculate the exact
702 * amount of space required to manage 'count' blocks - this space may
703 * be considerably less then the calculated radix due to the large
704 * RADIX values we use.
708 blst_radix_init(blmeta_t *scan, int64_t radix, int skip, swblk_t count)
712 swblk_t memindex = 0;
718 if (radix == BLIST_BMAP_RADIX) {
720 scan->bm_bighint = 0;
721 scan->u.bmu_bitmap = 0;
727 * Meta node. If allocating the entire object we can special
728 * case it. However, we need to figure out how much memory
729 * is required to manage 'count' blocks, so we continue on anyway.
733 scan->bm_bighint = 0;
734 scan->u.bmu_avail = 0;
737 radix /= BLIST_META_RADIX;
738 next_skip = ((u_int)skip / BLIST_META_RADIX);
740 for (i = 1; i <= skip; i += next_skip) {
741 if (count >= (swblk_t)radix) {
743 * Allocate the entire object
745 memindex = i + blst_radix_init(
746 ((scan) ? &scan[i] : NULL),
751 count -= (swblk_t)radix;
752 } else if (count > 0) {
754 * Allocate a partial object
756 memindex = i + blst_radix_init(
757 ((scan) ? &scan[i] : NULL),
765 * Add terminator and break out
768 scan[i].bm_bighint = (swblk_t)-1;
780 blst_radix_print(blmeta_t *scan, swblk_t blk, int64_t radix, int skip, int tab)
786 if (radix == BLIST_BMAP_RADIX) {
788 "%*.*s(%04x,%lld): bitmap %08x big=%d\n",
790 blk, (long long)radix,
797 if (scan->u.bmu_avail == 0) {
799 "%*.*s(%04x,%lld) ALL ALLOCATED\n",
806 if (scan->u.bmu_avail == radix) {
808 "%*.*s(%04x,%lld) ALL FREE\n",
817 "%*.*s(%04x,%lld): subtree (%d/%lld) big=%d {\n",
819 blk, (long long)radix,
825 radix /= BLIST_META_RADIX;
826 next_skip = ((u_int)skip / BLIST_META_RADIX);
829 for (i = 1; i <= skip; i += next_skip) {
830 if (scan[i].bm_bighint == (swblk_t)-1) {
832 "%*.*s(%04x,%lld): Terminator\n",
834 blk, (long long)radix
846 blk += (swblk_t)radix;
861 main(int ac, char **av)
867 for (i = 1; i < ac; ++i) {
868 const char *ptr = av[i];
870 size = strtol(ptr, NULL, 0);
874 fprintf(stderr, "Bad option: %s\n", ptr - 2);
877 bl = blist_create(size);
878 blist_free(bl, 0, size);
886 kprintf("%d/%d/%lld> ",
887 bl->bl_free, size, (long long)bl->bl_radix);
889 if (fgets(buf, sizeof(buf), stdin) == NULL)
893 if (sscanf(buf + 1, "%d", &count) == 1) {
894 blist_resize(&bl, count, 1);
903 if (sscanf(buf + 1, "%d", &count) == 1) {
904 swblk_t blk = blist_alloc(bl, count);
905 kprintf(" R=%04x\n", blk);
911 if (sscanf(buf + 1, "%x %d", &da, &count) == 2) {
912 blist_free(bl, da, count);
936 panic(const char *ctl, ...)
941 vfprintf(stderr, ctl, va);
942 fprintf(stderr, "\n");