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 * This code can be compiled stand-alone for debugging.
92 * $FreeBSD: src/sys/kern/subr_blist.c,v 1.5.2.2 2003/01/12 09:23:12 dillon Exp $
93 * $DragonFly: src/sys/kern/subr_blist.c,v 1.8 2008/08/10 22:09:50 dillon Exp $
98 #include <sys/param.h>
99 #include <sys/systm.h>
100 #include <sys/lock.h>
101 #include <sys/kernel.h>
102 #include <sys/blist.h>
103 #include <sys/malloc.h>
105 #include <vm/vm_object.h>
106 #include <vm/vm_kern.h>
107 #include <vm/vm_extern.h>
108 #include <vm/vm_page.h>
112 #ifndef BLIST_NO_DEBUG
116 #define SWAPBLK_NONE ((swblk_t)-1)
118 #include <sys/types.h>
124 #define kmalloc(a,b,c) malloc(a)
125 #define kfree(a,b) free(a)
127 #include <sys/blist.h>
129 void panic(const char *ctl, ...);
134 * static support functions
137 static swblk_t blst_leaf_alloc(blmeta_t *scan, swblk_t blk, int count);
138 static swblk_t blst_meta_alloc(blmeta_t *scan, swblk_t blk,
139 swblk_t count, swblk_t radix, int skip);
140 static void blst_leaf_free(blmeta_t *scan, swblk_t relblk, int count);
141 static void blst_meta_free(blmeta_t *scan, swblk_t freeBlk, swblk_t count,
142 swblk_t radix, int skip, swblk_t blk);
143 static void blst_copy(blmeta_t *scan, swblk_t blk, swblk_t radix,
144 swblk_t skip, blist_t dest, swblk_t count);
145 static swblk_t blst_radix_init(blmeta_t *scan, swblk_t radix,
146 int skip, swblk_t count);
148 static void blst_radix_print(blmeta_t *scan, swblk_t blk,
149 swblk_t radix, int skip, int tab);
153 static MALLOC_DEFINE(M_SWAP, "SWAP", "Swap space");
157 * blist_create() - create a blist capable of handling up to the specified
160 * blocks must be greater then 0
162 * The smallest blist consists of a single leaf node capable of
163 * managing BLIST_BMAP_RADIX blocks.
167 blist_create(swblk_t blocks)
174 * Calculate radix and skip field used for scanning.
176 radix = BLIST_BMAP_RADIX;
178 while (radix < blocks) {
179 radix *= BLIST_META_RADIX;
180 skip = (skip + 1) * BLIST_META_RADIX;
183 bl = kmalloc(sizeof(struct blist), M_SWAP, M_WAITOK);
185 bzero(bl, sizeof(*bl));
187 bl->bl_blocks = blocks;
188 bl->bl_radix = radix;
190 bl->bl_rootblks = 1 +
191 blst_radix_init(NULL, bl->bl_radix, bl->bl_skip, blocks);
192 bl->bl_root = kmalloc(sizeof(blmeta_t) * bl->bl_rootblks, M_SWAP, M_WAITOK);
194 #if defined(BLIST_DEBUG)
196 "BLIST representing %d blocks (%d MB of swap)"
197 ", requiring %dK of ram\n",
199 bl->bl_blocks * 4 / 1024,
200 (bl->bl_rootblks * sizeof(blmeta_t) + 1023) / 1024
202 kprintf("BLIST raw radix tree contains %d records\n", bl->bl_rootblks);
204 blst_radix_init(bl->bl_root, bl->bl_radix, bl->bl_skip, blocks);
210 blist_destroy(blist_t bl)
212 kfree(bl->bl_root, M_SWAP);
217 * blist_alloc() - reserve space in the block bitmap. Return the base
218 * of a contiguous region or SWAPBLK_NONE if space could
223 blist_alloc(blist_t bl, swblk_t count)
225 swblk_t blk = SWAPBLK_NONE;
228 if (bl->bl_radix == BLIST_BMAP_RADIX)
229 blk = blst_leaf_alloc(bl->bl_root, 0, count);
231 blk = blst_meta_alloc(bl->bl_root, 0, count, bl->bl_radix, bl->bl_skip);
232 if (blk != SWAPBLK_NONE)
233 bl->bl_free -= count;
239 * blist_free() - free up space in the block bitmap. Return the base
240 * of a contiguous region. Panic if an inconsistancy is
245 blist_free(blist_t bl, swblk_t blkno, swblk_t count)
248 if (bl->bl_radix == BLIST_BMAP_RADIX)
249 blst_leaf_free(bl->bl_root, blkno, count);
251 blst_meta_free(bl->bl_root, blkno, count, bl->bl_radix, bl->bl_skip, 0);
252 bl->bl_free += count;
257 * blist_resize() - resize an existing radix tree to handle the
258 * specified number of blocks. This will reallocate
259 * the tree and transfer the previous bitmap to the new
260 * one. When extending the tree you can specify whether
261 * the new blocks are to left allocated or freed.
265 blist_resize(blist_t *pbl, swblk_t count, int freenew)
267 blist_t newbl = blist_create(count);
271 if (count > save->bl_blocks)
272 count = save->bl_blocks;
273 blst_copy(save->bl_root, 0, save->bl_radix, save->bl_skip, newbl, count);
276 * If resizing upwards, should we free the new space or not?
278 if (freenew && count < newbl->bl_blocks) {
279 blist_free(newbl, count, newbl->bl_blocks - count);
287 * blist_print() - dump radix tree
291 blist_print(blist_t bl)
293 kprintf("BLIST {\n");
294 blst_radix_print(bl->bl_root, 0, bl->bl_radix, bl->bl_skip, 4);
300 /************************************************************************
301 * ALLOCATION SUPPORT FUNCTIONS *
302 ************************************************************************
304 * These support functions do all the actual work. They may seem
305 * rather longish, but that's because I've commented them up. The
306 * actual code is straight forward.
311 * blist_leaf_alloc() - allocate at a leaf in the radix tree (a bitmap).
313 * This is the core of the allocator and is optimized for the 1 block
314 * and the BLIST_BMAP_RADIX block allocation cases. Other cases are
315 * somewhat slower. The 1 block allocation case is log2 and extremely
320 blst_leaf_alloc(blmeta_t *scan, swblk_t blk, int count)
322 u_swblk_t orig = scan->u.bmu_bitmap;
326 * Optimize bitmap all-allocated case. Also, count = 1
327 * case assumes at least 1 bit is free in the bitmap, so
328 * we have to take care of this case here.
330 scan->bm_bighint = 0;
331 return(SWAPBLK_NONE);
335 * Optimized code to allocate one bit out of the bitmap
338 int j = BLIST_BMAP_RADIX/2;
341 mask = (u_swblk_t)-1 >> (BLIST_BMAP_RADIX/2);
344 if ((orig & mask) == 0) {
351 scan->u.bmu_bitmap &= ~(1 << r);
354 if (count <= BLIST_BMAP_RADIX) {
356 * non-optimized code to allocate N bits out of the bitmap.
357 * The more bits, the faster the code runs. It will run
358 * the slowest allocating 2 bits, but since there aren't any
359 * memory ops in the core loop (or shouldn't be, anyway),
360 * you probably won't notice the difference.
363 int n = BLIST_BMAP_RADIX - count;
366 mask = (u_swblk_t)-1 >> n;
368 for (j = 0; j <= n; ++j) {
369 if ((orig & mask) == mask) {
370 scan->u.bmu_bitmap &= ~mask;
377 * We couldn't allocate count in this subtree, update bighint.
379 scan->bm_bighint = count - 1;
380 return(SWAPBLK_NONE);
384 * blist_meta_alloc() - allocate at a meta in the radix tree.
386 * Attempt to allocate at a meta node. If we can't, we update
387 * bighint and return a failure. Updating bighint optimize future
388 * calls that hit this node. We have to check for our collapse cases
389 * and we have a few optimizations strewn in as well.
393 blst_meta_alloc(blmeta_t *scan, swblk_t blk, swblk_t count,
394 swblk_t radix, int skip)
397 int next_skip = ((u_int)skip / BLIST_META_RADIX);
399 if (scan->u.bmu_avail == 0) {
401 * ALL-ALLOCATED special case
403 scan->bm_bighint = count;
404 return(SWAPBLK_NONE);
407 if (scan->u.bmu_avail == radix) {
408 radix /= BLIST_META_RADIX;
411 * ALL-FREE special case, initialize uninitialize
414 for (i = 1; i <= skip; i += next_skip) {
415 if (scan[i].bm_bighint == (swblk_t)-1)
417 if (next_skip == 1) {
418 scan[i].u.bmu_bitmap = (u_swblk_t)-1;
419 scan[i].bm_bighint = BLIST_BMAP_RADIX;
421 scan[i].bm_bighint = radix;
422 scan[i].u.bmu_avail = radix;
426 radix /= BLIST_META_RADIX;
429 for (i = 1; i <= skip; i += next_skip) {
430 if (count <= scan[i].bm_bighint) {
432 * count fits in object
435 if (next_skip == 1) {
436 r = blst_leaf_alloc(&scan[i], blk, count);
438 r = blst_meta_alloc(&scan[i], blk, count, radix, next_skip - 1);
440 if (r != SWAPBLK_NONE) {
441 scan->u.bmu_avail -= count;
442 if (scan->bm_bighint > scan->u.bmu_avail)
443 scan->bm_bighint = scan->u.bmu_avail;
446 } else if (scan[i].bm_bighint == (swblk_t)-1) {
451 } else if (count > radix) {
453 * count does not fit in object even if it were
456 panic("blist_meta_alloc: allocation too large");
462 * We couldn't allocate count in this subtree, update bighint.
464 if (scan->bm_bighint >= count)
465 scan->bm_bighint = count - 1;
466 return(SWAPBLK_NONE);
470 * BLST_LEAF_FREE() - free allocated block from leaf bitmap
475 blst_leaf_free(blmeta_t *scan, swblk_t blk, int count)
478 * free some data in this bitmap
481 * 0000111111111110000
485 int n = blk & (BLIST_BMAP_RADIX - 1);
488 mask = ((u_swblk_t)-1 << n) &
489 ((u_swblk_t)-1 >> (BLIST_BMAP_RADIX - count - n));
491 if (scan->u.bmu_bitmap & mask)
492 panic("blst_radix_free: freeing free block");
493 scan->u.bmu_bitmap |= mask;
496 * We could probably do a better job here. We are required to make
497 * bighint at least as large as the biggest contiguous block of
498 * data. If we just shoehorn it, a little extra overhead will
499 * be incured on the next allocation (but only that one typically).
501 scan->bm_bighint = BLIST_BMAP_RADIX;
505 * BLST_META_FREE() - free allocated blocks from radix tree meta info
507 * This support routine frees a range of blocks from the bitmap.
508 * The range must be entirely enclosed by this radix node. If a
509 * meta node, we break the range down recursively to free blocks
510 * in subnodes (which means that this code can free an arbitrary
511 * range whereas the allocation code cannot allocate an arbitrary
516 blst_meta_free(blmeta_t *scan, swblk_t freeBlk, swblk_t count,
517 swblk_t radix, int skip, swblk_t blk)
520 int next_skip = ((u_int)skip / BLIST_META_RADIX);
523 kprintf("FREE (%x,%d) FROM (%x,%d)\n",
529 if (scan->u.bmu_avail == 0) {
531 * ALL-ALLOCATED special case, with possible
532 * shortcut to ALL-FREE special case.
534 scan->u.bmu_avail = count;
535 scan->bm_bighint = count;
537 if (count != radix) {
538 for (i = 1; i <= skip; i += next_skip) {
539 if (scan[i].bm_bighint == (swblk_t)-1)
541 scan[i].bm_bighint = 0;
542 if (next_skip == 1) {
543 scan[i].u.bmu_bitmap = 0;
545 scan[i].u.bmu_avail = 0;
551 scan->u.bmu_avail += count;
552 /* scan->bm_bighint = radix; */
556 * ALL-FREE special case.
559 if (scan->u.bmu_avail == radix)
561 if (scan->u.bmu_avail > radix)
562 panic("blst_meta_free: freeing already free blocks (%d) %d/%d", count, scan->u.bmu_avail, radix);
565 * Break the free down into its components
568 radix /= BLIST_META_RADIX;
570 i = (freeBlk - blk) / radix;
572 i = i * next_skip + 1;
574 while (i <= skip && blk < freeBlk + count) {
577 v = blk + radix - freeBlk;
581 if (scan->bm_bighint == (swblk_t)-1)
582 panic("blst_meta_free: freeing unexpected range");
584 if (next_skip == 1) {
585 blst_leaf_free(&scan[i], freeBlk, v);
587 blst_meta_free(&scan[i], freeBlk, v, radix, next_skip - 1, blk);
589 if (scan->bm_bighint < scan[i].bm_bighint)
590 scan->bm_bighint = scan[i].bm_bighint;
599 * BLIST_RADIX_COPY() - copy one radix tree to another
601 * Locates free space in the source tree and frees it in the destination
602 * tree. The space may not already be free in the destination.
606 blst_copy(blmeta_t *scan, swblk_t blk, swblk_t radix,
607 swblk_t skip, blist_t dest, swblk_t count)
616 if (radix == BLIST_BMAP_RADIX) {
617 u_swblk_t v = scan->u.bmu_bitmap;
619 if (v == (u_swblk_t)-1) {
620 blist_free(dest, blk, count);
624 for (i = 0; i < BLIST_BMAP_RADIX && i < count; ++i) {
626 blist_free(dest, blk + i, 1);
636 if (scan->u.bmu_avail == 0) {
638 * Source all allocated, leave dest allocated
642 if (scan->u.bmu_avail == radix) {
644 * Source all free, free entire dest
647 blist_free(dest, blk, count);
649 blist_free(dest, blk, radix);
654 radix /= BLIST_META_RADIX;
655 next_skip = ((u_int)skip / BLIST_META_RADIX);
657 for (i = 1; count && i <= skip; i += next_skip) {
658 if (scan[i].bm_bighint == (swblk_t)-1)
661 if (count >= radix) {
689 * BLST_RADIX_INIT() - initialize radix tree
691 * Initialize our meta structures and bitmaps and calculate the exact
692 * amount of space required to manage 'count' blocks - this space may
693 * be considerably less then the calculated radix due to the large
694 * RADIX values we use.
698 blst_radix_init(blmeta_t *scan, swblk_t radix, int skip, swblk_t count)
702 swblk_t memindex = 0;
708 if (radix == BLIST_BMAP_RADIX) {
710 scan->bm_bighint = 0;
711 scan->u.bmu_bitmap = 0;
717 * Meta node. If allocating the entire object we can special
718 * case it. However, we need to figure out how much memory
719 * is required to manage 'count' blocks, so we continue on anyway.
723 scan->bm_bighint = 0;
724 scan->u.bmu_avail = 0;
727 radix /= BLIST_META_RADIX;
728 next_skip = ((u_int)skip / BLIST_META_RADIX);
730 for (i = 1; i <= skip; i += next_skip) {
731 if (count >= radix) {
733 * Allocate the entire object
735 memindex = i + blst_radix_init(
736 ((scan) ? &scan[i] : NULL),
742 } else if (count > 0) {
744 * Allocate a partial object
746 memindex = i + blst_radix_init(
747 ((scan) ? &scan[i] : NULL),
755 * Add terminator and break out
758 scan[i].bm_bighint = (swblk_t)-1;
770 blst_radix_print(blmeta_t *scan, swblk_t blk, swblk_t radix, int skip, int tab)
776 if (radix == BLIST_BMAP_RADIX) {
778 "%*.*s(%04x,%d): bitmap %08x big=%d\n",
787 if (scan->u.bmu_avail == 0) {
789 "%*.*s(%04x,%d) ALL ALLOCATED\n",
796 if (scan->u.bmu_avail == radix) {
798 "%*.*s(%04x,%d) ALL FREE\n",
807 "%*.*s(%04x,%d): subtree (%d/%d) big=%d {\n",
815 radix /= BLIST_META_RADIX;
816 next_skip = ((u_int)skip / BLIST_META_RADIX);
819 for (i = 1; i <= skip; i += next_skip) {
820 if (scan[i].bm_bighint == (swblk_t)-1) {
822 "%*.*s(%04x,%d): Terminator\n",
851 main(int ac, char **av)
857 for (i = 1; i < ac; ++i) {
858 const char *ptr = av[i];
860 size = strtol(ptr, NULL, 0);
864 fprintf(stderr, "Bad option: %s\n", ptr - 2);
867 bl = blist_create(size);
868 blist_free(bl, 0, size);
876 kprintf("%d/%d/%d> ", bl->bl_free, size, bl->bl_radix);
878 if (fgets(buf, sizeof(buf), stdin) == NULL)
882 if (sscanf(buf + 1, "%d", &count) == 1) {
883 blist_resize(&bl, count, 1);
891 if (sscanf(buf + 1, "%d", &count) == 1) {
892 swblk_t blk = blist_alloc(bl, count);
893 kprintf(" R=%04x\n", blk);
899 if (sscanf(buf + 1, "%x %d", &da, &count) == 2) {
900 blist_free(bl, da, count);
924 panic(const char *ctl, ...)
929 vfprintf(stderr, ctl, va);
930 fprintf(stderr, "\n");