/*-
* Copyright (c) 1998 Matthew Dillon. All Rights Reserved.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* BLIST.C - Bitmap allocator/deallocator, using a radix tree with hinting
*
* 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 than to return
* BLIST_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 than 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 laid out recursively using a
* linear array. Each meta node is immediately followed (laid 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 than
* 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 affect 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.
*/
/*
* blmeta and bl_bitmap_t MUST be a power of 2 in size.
*/
typedef struct blmeta {
union {
blist_blkno_t bmu_avail; /* space available under us */
blist_bitmap_t bmu_bitmap; /* bitmap if we are a leaf */
} u;
blist_blkno_t bm_bighint; /* biggest contiguous block hint*/
} blmeta_t;
struct blist {
blist_blkno_t bl_blocks; /* area of coverage */
blist_blkno_t bl_radix; /* coverage radix */
blist_blkno_t bl_skip; /* starting skip */
blist_blkno_t bl_free; /* number of free blocks */
blmeta_t *bl_root; /* root of radix tree */
blist_blkno_t bl_rootblks; /* blks allocated for tree */
};
/*
* blist_create() - create a blist capable of handling up to the specified
* number of blocks
*
* blocks must be greater than 0
*
* The smallest blist consists of a single leaf node capable of
* managing BLIST_BMAP_RADIX blocks.
*/
/*
* blist_fill() - mark a region in the block bitmap as off-limits
* to the allocator (i.e. allocate it), ignoring any
* existing allocations. Return the number of blocks
* actually filled that were free before the call.
*/
/*
* 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, blist_blkno_t count, int freenew)
{
blist_t newbl = blist_create(count);
blist_t save = *pbl;
/*
* 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);
}
/************************************************************************
* 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.
*/
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(BLIST_NONE);
}
if (count == 1) {
/*
* Optimized code to allocate one bit out of the bitmap
*/
blist_bitmap_t mask;
int j = BLIST_BMAP_RADIX/2;
int r = 0;
while (j) {
if ((orig & mask) == 0) {
r += j;
orig >>= j;
}
j >>= 1;
mask >>= j;
}
scan->u.bmu_bitmap &= ~((blist_bitmap_t)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;
blist_bitmap_t mask;
mask = (blist_bitmap_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(BLIST_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.
*/
if (scan->u.bmu_avail == 0) {
/*
* ALL-ALLOCATED special case
*/
scan->bm_bighint = count;
return(BLIST_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 == (blist_blkno_t)-1)
break;
if (next_skip == 1) {
scan[i].u.bmu_bitmap = (blist_bitmap_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 (scan[i].bm_bighint == (blist_blkno_t)-1) {
/*
* Terminator
*/
break;
} else if (count <= scan[i].bm_bighint) {
/*
* count fits in object
*/
blist_blkno_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 != BLIST_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 (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(BLIST_NONE);
}
static void
blst_leaf_free(
blmeta_t *scan,
blist_blkno_t blk,
int count
) {
/*
* free some data in this bitmap
*
* e.g.
* 0000111111111110000
* \_________/\__/
* v n
*/
int n = blk & (BLIST_BMAP_RADIX - 1);
blist_bitmap_t 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).
*/
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 == (blist_blkno_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; */
}
/*
* 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.
*/
/*
* BLST_LEAF_FILL() - allocate specific blocks in leaf bitmap
*
* This routine allocates all blocks in the specified range
* regardless of any existing allocations in that range. Returns
* the number of blocks allocated by the call.
*/
static int
blst_leaf_fill(blmeta_t *scan, blist_blkno_t blk, int count)
{
int n = blk & (BLIST_BMAP_RADIX - 1);
int nblks;
blist_bitmap_t mask, bitmap;
/* Count the number of blocks we're about to allocate */
bitmap = scan->u.bmu_bitmap & mask;
for (nblks = 0; bitmap != 0; nblks++)
bitmap &= bitmap - 1;
scan->u.bmu_bitmap &= ~mask;
return nblks;
}
/*
* BLIST_META_FILL() - allocate specific blocks at a meta node
*
* This routine allocates the specified range of blocks,
* regardless of any existing allocations in the range. The
* range must be within the extent of this node. Returns the
* number of blocks allocated by the call.
*/
static blist_blkno_t
blst_meta_fill(
blmeta_t *scan,
blist_blkno_t allocBlk,
blist_blkno_t count,
blist_blkno_t radix,
blist_blkno_t skip,
blist_blkno_t blk
) {
blist_blkno_t i;
blist_blkno_t next_skip = (skip / BLIST_META_RADIX);
blist_blkno_t nblks = 0;
if (count == radix || scan->u.bmu_avail == 0) {
/*
* ALL-ALLOCATED special case
*/
nblks = scan->u.bmu_avail;
scan->u.bmu_avail = 0;
scan->bm_bighint = count;
return nblks;
}
if (count > radix)
panic("blist_meta_fill: allocation too large");
if (scan->u.bmu_avail == radix) {
radix /= BLIST_META_RADIX;
/*
* ALL-FREE special case, initialize sublevel
*/
for (i = 1; i <= skip; i += next_skip) {
if (scan[i].bm_bighint == (blist_blkno_t)-1)
break;
if (next_skip == 1) {
scan[i].u.bmu_bitmap = (blist_bitmap_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;
}
i = (allocBlk - blk) / radix;
blk += i * radix;
i = i * next_skip + 1;
while (i <= skip && blk < allocBlk + count) {
blist_blkno_t v;
v = blk + radix - allocBlk;
if (v > count)
v = count;
if (scan->bm_bighint == (blist_blkno_t)-1)
panic("blst_meta_fill: filling unexpected range");
/*
* 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 than the calculated radix due to the large
* RADIX values we use.
*/
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;
}
