/* * BLIST.C - Bitmap allocator/deallocator, using a radix tree with hinting * * (c)Copyright 1998, Matthew Dillon. Terms for use and redistribution * are covered by the BSD Copyright as found in /usr/src/COPYRIGHT. * * This module implements a general bitmap allocator/deallocator. The * allocator eats around 2 bits per 'block'. The module does not * try to interpret the meaning of a 'block' other then to return * SWAPBLK_NONE on an allocation failure. * * A radix tree is used to maintain the bitmap. Two radix constants are * involved: One for the bitmaps contained in the leaf nodes (typically * 32), and one for the meta nodes (typically 16). Both meta and leaf * nodes have a hint field. This field gives us a hint as to the largest * free contiguous range of blocks under the node. It may contain a * value that is too high, but will never contain a value that is too * low. When the radix tree is searched, allocation failures in subtrees * update the hint. * * The radix tree also implements two collapsed states for meta nodes: * the ALL-ALLOCATED state and the ALL-FREE state. If a meta node is * in either of these two states, all information contained underneath * the node is considered stale. These states are used to optimize * allocation and freeing operations. * * The hinting greatly increases code efficiency for allocations while * the general radix structure optimizes both allocations and frees. The * radix tree should be able to operate well no matter how much * fragmentation there is and no matter how large a bitmap is used. * * Unlike the rlist code, the blist code wires all necessary memory at * creation time. Neither allocations nor frees require interaction with * the memory subsystem. In contrast, the rlist code may allocate memory * on an rlist_free() call. The non-blocking features of the blist code * are used to great advantage in the swap code (vm/nswap_pager.c). The * rlist code uses a little less overall memory then the blist code (but * due to swap interleaving not all that much less), but the blist code * scales much, much better. * * LAYOUT: The radix tree is layed out recursively using a * linear array. Each meta node is immediately followed (layed out * sequentially in memory) by BLIST_META_RADIX lower level nodes. This * is a recursive structure but one that can be easily scanned through * a very simple 'skip' calculation. In order to support large radixes, * portions of the tree may reside outside our memory allocation. We * handle this with an early-termination optimization (when bighint is * set to -1) on the scan. The memory allocation is only large enough * to cover the number of blocks requested at creation time even if it * must be encompassed in larger root-node radix. * * NOTE: the allocator cannot currently allocate more then * BLIST_BMAP_RADIX blocks per call. It will panic with 'allocation too * large' if you try. This is an area that could use improvement. The * radix is large enough that this restriction does not effect the swap * system, though. Currently only the allocation code is effected by * this algorithmic unfeature. The freeing code can handle arbitrary * ranges. * * This code can be compiled stand-alone for debugging. * * $FreeBSD: src/sys/kern/subr_blist.c,v 1.5.2.2 2003/01/12 09:23:12 dillon Exp $ * $DragonFly: src/sys/kern/subr_blist.c,v 1.2 2003/06/17 04:28:41 dillon Exp $ */ #ifdef _KERNEL #include #include #include #include #include #include #include #include #include #include #include #else #ifndef BLIST_NO_DEBUG #define BLIST_DEBUG #endif #define SWAPBLK_NONE ((daddr_t)-1) #include #include #include #include #include #define malloc(a,b,c) malloc(a) #define free(a,b) free(a) typedef unsigned int u_daddr_t; #include void panic(const char *ctl, ...); #endif /* * static support functions */ static daddr_t blst_leaf_alloc(blmeta_t *scan, daddr_t blk, int count); static daddr_t blst_meta_alloc(blmeta_t *scan, daddr_t blk, daddr_t count, daddr_t radix, int skip); static void blst_leaf_free(blmeta_t *scan, daddr_t relblk, int count); static void blst_meta_free(blmeta_t *scan, daddr_t freeBlk, daddr_t count, daddr_t radix, int skip, daddr_t blk); static void blst_copy(blmeta_t *scan, daddr_t blk, daddr_t radix, daddr_t skip, blist_t dest, daddr_t count); static daddr_t blst_radix_init(blmeta_t *scan, daddr_t radix, int skip, daddr_t count); #ifndef _KERNEL static void blst_radix_print(blmeta_t *scan, daddr_t blk, daddr_t radix, int skip, int tab); #endif #ifdef _KERNEL static MALLOC_DEFINE(M_SWAP, "SWAP", "Swap space"); #endif /* * blist_create() - create a blist capable of handling up to the specified * number of blocks * * blocks must be greater then 0 * * The smallest blist consists of a single leaf node capable of * managing BLIST_BMAP_RADIX blocks. */ blist_t blist_create(daddr_t blocks) { blist_t bl; int radix; int skip = 0; /* * Calculate radix and skip field used for scanning. */ radix = BLIST_BMAP_RADIX; while (radix < blocks) { radix *= BLIST_META_RADIX; skip = (skip + 1) * BLIST_META_RADIX; } bl = malloc(sizeof(struct blist), M_SWAP, M_WAITOK); bzero(bl, sizeof(*bl)); bl->bl_blocks = blocks; bl->bl_radix = radix; bl->bl_skip = skip; bl->bl_rootblks = 1 + blst_radix_init(NULL, bl->bl_radix, bl->bl_skip, blocks); bl->bl_root = malloc(sizeof(blmeta_t) * bl->bl_rootblks, M_SWAP, M_WAITOK); #if defined(BLIST_DEBUG) printf( "BLIST representing %d blocks (%d MB of swap)" ", requiring %dK of ram\n", bl->bl_blocks, bl->bl_blocks * 4 / 1024, (bl->bl_rootblks * sizeof(blmeta_t) + 1023) / 1024 ); printf("BLIST raw radix tree contains %d records\n", bl->bl_rootblks); #endif blst_radix_init(bl->bl_root, bl->bl_radix, bl->bl_skip, blocks); return(bl); } void blist_destroy(blist_t bl) { free(bl->bl_root, M_SWAP); free(bl, M_SWAP); } /* * blist_alloc() - reserve space in the block bitmap. Return the base * of a contiguous region or SWAPBLK_NONE if space could * not be allocated. */ daddr_t blist_alloc(blist_t bl, daddr_t count) { daddr_t blk = SWAPBLK_NONE; if (bl) { if (bl->bl_radix == BLIST_BMAP_RADIX) blk = blst_leaf_alloc(bl->bl_root, 0, count); else blk = blst_meta_alloc(bl->bl_root, 0, count, bl->bl_radix, bl->bl_skip); if (blk != SWAPBLK_NONE) bl->bl_free -= count; } return(blk); } /* * blist_free() - free up space in the block bitmap. Return the base * of a contiguous region. Panic if an inconsistancy is * found. */ void blist_free(blist_t bl, daddr_t blkno, daddr_t count) { if (bl) { if (bl->bl_radix == BLIST_BMAP_RADIX) blst_leaf_free(bl->bl_root, blkno, count); else blst_meta_free(bl->bl_root, blkno, count, bl->bl_radix, bl->bl_skip, 0); bl->bl_free += count; } } /* * blist_resize() - resize an existing radix tree to handle the * specified number of blocks. This will reallocate * the tree and transfer the previous bitmap to the new * one. When extending the tree you can specify whether * the new blocks are to left allocated or freed. */ void blist_resize(blist_t *pbl, daddr_t count, int freenew) { blist_t newbl = blist_create(count); blist_t save = *pbl; *pbl = newbl; if (count > save->bl_blocks) count = save->bl_blocks; blst_copy(save->bl_root, 0, save->bl_radix, save->bl_skip, newbl, count); /* * If resizing upwards, should we free the new space or not? */ if (freenew && count < newbl->bl_blocks) { blist_free(newbl, count, newbl->bl_blocks - count); } blist_destroy(save); } #ifdef BLIST_DEBUG /* * blist_print() - dump radix tree */ void blist_print(blist_t bl) { printf("BLIST {\n"); blst_radix_print(bl->bl_root, 0, bl->bl_radix, bl->bl_skip, 4); printf("}\n"); } #endif /************************************************************************ * ALLOCATION SUPPORT FUNCTIONS * ************************************************************************ * * These support functions do all the actual work. They may seem * rather longish, but that's because I've commented them up. The * actual code is straight forward. * */ /* * blist_leaf_alloc() - allocate at a leaf in the radix tree (a bitmap). * * This is the core of the allocator and is optimized for the 1 block * and the BLIST_BMAP_RADIX block allocation cases. Other cases are * somewhat slower. The 1 block allocation case is log2 and extremely * quick. */ static daddr_t blst_leaf_alloc( blmeta_t *scan, daddr_t blk, int count ) { u_daddr_t orig = scan->u.bmu_bitmap; if (orig == 0) { /* * Optimize bitmap all-allocated case. Also, count = 1 * case assumes at least 1 bit is free in the bitmap, so * we have to take care of this case here. */ scan->bm_bighint = 0; return(SWAPBLK_NONE); } if (count == 1) { /* * Optimized code to allocate one bit out of the bitmap */ u_daddr_t mask; int j = BLIST_BMAP_RADIX/2; int r = 0; mask = (u_daddr_t)-1 >> (BLIST_BMAP_RADIX/2); while (j) { if ((orig & mask) == 0) { r += j; orig >>= j; } j >>= 1; mask >>= j; } scan->u.bmu_bitmap &= ~(1 << r); return(blk + r); } if (count <= BLIST_BMAP_RADIX) { /* * non-optimized code to allocate N bits out of the bitmap. * The more bits, the faster the code runs. It will run * the slowest allocating 2 bits, but since there aren't any * memory ops in the core loop (or shouldn't be, anyway), * you probably won't notice the difference. */ int j; int n = BLIST_BMAP_RADIX - count; u_daddr_t mask; mask = (u_daddr_t)-1 >> n; for (j = 0; j <= n; ++j) { if ((orig & mask) == mask) { scan->u.bmu_bitmap &= ~mask; return(blk + j); } mask = (mask << 1); } } /* * We couldn't allocate count in this subtree, update bighint. */ scan->bm_bighint = count - 1; return(SWAPBLK_NONE); } /* * blist_meta_alloc() - allocate at a meta in the radix tree. * * Attempt to allocate at a meta node. If we can't, we update * bighint and return a failure. Updating bighint optimize future * calls that hit this node. We have to check for our collapse cases * and we have a few optimizations strewn in as well. */ static daddr_t blst_meta_alloc( blmeta_t *scan, daddr_t blk, daddr_t count, daddr_t radix, int skip ) { int i; int next_skip = ((u_int)skip / BLIST_META_RADIX); if (scan->u.bmu_avail == 0) { /* * ALL-ALLOCATED special case */ scan->bm_bighint = count; return(SWAPBLK_NONE); } if (scan->u.bmu_avail == radix) { radix /= BLIST_META_RADIX; /* * ALL-FREE special case, initialize uninitialize * sublevel. */ for (i = 1; i <= skip; i += next_skip) { if (scan[i].bm_bighint == (daddr_t)-1) break; if (next_skip == 1) { scan[i].u.bmu_bitmap = (u_daddr_t)-1; scan[i].bm_bighint = BLIST_BMAP_RADIX; } else { scan[i].bm_bighint = radix; scan[i].u.bmu_avail = radix; } } } else { radix /= BLIST_META_RADIX; } for (i = 1; i <= skip; i += next_skip) { if (count <= scan[i].bm_bighint) { /* * count fits in object */ daddr_t r; if (next_skip == 1) { r = blst_leaf_alloc(&scan[i], blk, count); } else { r = blst_meta_alloc(&scan[i], blk, count, radix, next_skip - 1); } if (r != SWAPBLK_NONE) { scan->u.bmu_avail -= count; if (scan->bm_bighint > scan->u.bmu_avail) scan->bm_bighint = scan->u.bmu_avail; return(r); } } else if (scan[i].bm_bighint == (daddr_t)-1) { /* * Terminator */ break; } else if (count > radix) { /* * count does not fit in object even if it were * complete free. */ panic("blist_meta_alloc: allocation too large"); } blk += radix; } /* * We couldn't allocate count in this subtree, update bighint. */ if (scan->bm_bighint >= count) scan->bm_bighint = count - 1; return(SWAPBLK_NONE); } /* * BLST_LEAF_FREE() - free allocated block from leaf bitmap * */ static void blst_leaf_free( blmeta_t *scan, daddr_t blk, int count ) { /* * free some data in this bitmap * * e.g. * 0000111111111110000 * \_________/\__/ * v n */ int n = blk & (BLIST_BMAP_RADIX - 1); u_daddr_t mask; mask = ((u_daddr_t)-1 << n) & ((u_daddr_t)-1 >> (BLIST_BMAP_RADIX - count - n)); if (scan->u.bmu_bitmap & mask) panic("blst_radix_free: freeing free block"); scan->u.bmu_bitmap |= mask; /* * We could probably do a better job here. We are required to make * bighint at least as large as the biggest contiguous block of * data. If we just shoehorn it, a little extra overhead will * be incured on the next allocation (but only that one typically). */ scan->bm_bighint = BLIST_BMAP_RADIX; } /* * BLST_META_FREE() - free allocated blocks from radix tree meta info * * This support routine frees a range of blocks from the bitmap. * The range must be entirely enclosed by this radix node. If a * meta node, we break the range down recursively to free blocks * in subnodes (which means that this code can free an arbitrary * range whereas the allocation code cannot allocate an arbitrary * range). */ static void blst_meta_free( blmeta_t *scan, daddr_t freeBlk, daddr_t count, daddr_t radix, int skip, daddr_t blk ) { int i; int next_skip = ((u_int)skip / BLIST_META_RADIX); #if 0 printf("FREE (%x,%d) FROM (%x,%d)\n", freeBlk, count, blk, radix ); #endif if (scan->u.bmu_avail == 0) { /* * ALL-ALLOCATED special case, with possible * shortcut to ALL-FREE special case. */ scan->u.bmu_avail = count; scan->bm_bighint = count; if (count != radix) { for (i = 1; i <= skip; i += next_skip) { if (scan[i].bm_bighint == (daddr_t)-1) break; scan[i].bm_bighint = 0; if (next_skip == 1) { scan[i].u.bmu_bitmap = 0; } else { scan[i].u.bmu_avail = 0; } } /* fall through */ } } else { scan->u.bmu_avail += count; /* scan->bm_bighint = radix; */ } /* * ALL-FREE special case. */ if (scan->u.bmu_avail == radix) return; if (scan->u.bmu_avail > radix) panic("blst_meta_free: freeing already free blocks (%d) %d/%d", count, scan->u.bmu_avail, radix); /* * Break the free down into its components */ radix /= BLIST_META_RADIX; i = (freeBlk - blk) / radix; blk += i * radix; i = i * next_skip + 1; while (i <= skip && blk < freeBlk + count) { daddr_t v; v = blk + radix - freeBlk; if (v > count) v = count; if (scan->bm_bighint == (daddr_t)-1) panic("blst_meta_free: freeing unexpected range"); if (next_skip == 1) { blst_leaf_free(&scan[i], freeBlk, v); } else { blst_meta_free(&scan[i], freeBlk, v, radix, next_skip - 1, blk); } if (scan->bm_bighint < scan[i].bm_bighint) scan->bm_bighint = scan[i].bm_bighint; count -= v; freeBlk += v; blk += radix; i += next_skip; } } /* * BLIST_RADIX_COPY() - copy one radix tree to another * * Locates free space in the source tree and frees it in the destination * tree. The space may not already be free in the destination. */ static void blst_copy( blmeta_t *scan, daddr_t blk, daddr_t radix, daddr_t skip, blist_t dest, daddr_t count ) { int next_skip; int i; /* * Leaf node */ if (radix == BLIST_BMAP_RADIX) { u_daddr_t v = scan->u.bmu_bitmap; if (v == (u_daddr_t)-1) { blist_free(dest, blk, count); } else if (v != 0) { int i; for (i = 0; i < BLIST_BMAP_RADIX && i < count; ++i) { if (v & (1 << i)) blist_free(dest, blk + i, 1); } } return; } /* * Meta node */ if (scan->u.bmu_avail == 0) { /* * Source all allocated, leave dest allocated */ return; } if (scan->u.bmu_avail == radix) { /* * Source all free, free entire dest */ if (count < radix) blist_free(dest, blk, count); else blist_free(dest, blk, radix); return; } radix /= BLIST_META_RADIX; next_skip = ((u_int)skip / BLIST_META_RADIX); for (i = 1; count && i <= skip; i += next_skip) { if (scan[i].bm_bighint == (daddr_t)-1) break; if (count >= radix) { blst_copy( &scan[i], blk, radix, next_skip - 1, dest, radix ); count -= radix; } else { if (count) { blst_copy( &scan[i], blk, radix, next_skip - 1, dest, count ); } count = 0; } blk += radix; } } /* * BLST_RADIX_INIT() - initialize radix tree * * Initialize our meta structures and bitmaps and calculate the exact * amount of space required to manage 'count' blocks - this space may * be considerably less then the calculated radix due to the large * RADIX values we use. */ static daddr_t blst_radix_init(blmeta_t *scan, daddr_t radix, int skip, daddr_t count) { int i; int next_skip; daddr_t memindex = 0; /* * Leaf node */ if (radix == BLIST_BMAP_RADIX) { if (scan) { scan->bm_bighint = 0; scan->u.bmu_bitmap = 0; } return(memindex); } /* * Meta node. If allocating the entire object we can special * case it. However, we need to figure out how much memory * is required to manage 'count' blocks, so we continue on anyway. */ if (scan) { scan->bm_bighint = 0; scan->u.bmu_avail = 0; } radix /= BLIST_META_RADIX; next_skip = ((u_int)skip / BLIST_META_RADIX); for (i = 1; i <= skip; i += next_skip) { if (count >= radix) { /* * Allocate the entire object */ memindex = i + blst_radix_init( ((scan) ? &scan[i] : NULL), radix, next_skip - 1, radix ); count -= radix; } else if (count > 0) { /* * Allocate a partial object */ memindex = i + blst_radix_init( ((scan) ? &scan[i] : NULL), radix, next_skip - 1, count ); count = 0; } else { /* * Add terminator and break out */ if (scan) scan[i].bm_bighint = (daddr_t)-1; break; } } if (memindex < i) memindex = i; return(memindex); } #ifdef BLIST_DEBUG static void blst_radix_print(blmeta_t *scan, daddr_t blk, daddr_t radix, int skip, int tab) { int i; int next_skip; int lastState = 0; if (radix == BLIST_BMAP_RADIX) { printf( "%*.*s(%04x,%d): bitmap %08x big=%d\n", tab, tab, "", blk, radix, scan->u.bmu_bitmap, scan->bm_bighint ); return; } if (scan->u.bmu_avail == 0) { printf( "%*.*s(%04x,%d) ALL ALLOCATED\n", tab, tab, "", blk, radix ); return; } if (scan->u.bmu_avail == radix) { printf( "%*.*s(%04x,%d) ALL FREE\n", tab, tab, "", blk, radix ); return; } printf( "%*.*s(%04x,%d): subtree (%d/%d) big=%d {\n", tab, tab, "", blk, radix, scan->u.bmu_avail, radix, scan->bm_bighint ); radix /= BLIST_META_RADIX; next_skip = ((u_int)skip / BLIST_META_RADIX); tab += 4; for (i = 1; i <= skip; i += next_skip) { if (scan[i].bm_bighint == (daddr_t)-1) { printf( "%*.*s(%04x,%d): Terminator\n", tab, tab, "", blk, radix ); lastState = 0; break; } blst_radix_print( &scan[i], blk, radix, next_skip - 1, tab ); blk += radix; } tab -= 4; printf( "%*.*s}\n", tab, tab, "" ); } #endif #ifdef BLIST_DEBUG int main(int ac, char **av) { int size = 1024; int i; blist_t bl; for (i = 1; i < ac; ++i) { const char *ptr = av[i]; if (*ptr != '-') { size = strtol(ptr, NULL, 0); continue; } ptr += 2; fprintf(stderr, "Bad option: %s\n", ptr - 2); exit(1); } bl = blist_create(size); blist_free(bl, 0, size); for (;;) { char buf[1024]; daddr_t da = 0; daddr_t count = 0; printf("%d/%d/%d> ", bl->bl_free, size, bl->bl_radix); fflush(stdout); if (fgets(buf, sizeof(buf), stdin) == NULL) break; switch(buf[0]) { case 'r': if (sscanf(buf + 1, "%d", &count) == 1) { blist_resize(&bl, count, 1); } else { printf("?\n"); } case 'p': blist_print(bl); break; case 'a': if (sscanf(buf + 1, "%d", &count) == 1) { daddr_t blk = blist_alloc(bl, count); printf(" R=%04x\n", blk); } else { printf("?\n"); } break; case 'f': if (sscanf(buf + 1, "%x %d", &da, &count) == 2) { blist_free(bl, da, count); } else { printf("?\n"); } break; case '?': case 'h': puts( "p -print\n" "a %d -allocate\n" "f %x %d -free\n" "r %d -resize\n" "h/? -help" ); break; default: printf("?\n"); break; } } return(0); } void panic(const char *ctl, ...) { va_list va; va_start(va, ctl); vfprintf(stderr, ctl, va); fprintf(stderr, "\n"); va_end(va); exit(1); } #endif