ref: 21eb277c5a5d3178eed36c23466cd4abdede5122
dir: /lib/std/bytealloc.myr/
use sys
use "die"
use "extremum"
use "memops"
use "syswrap"
use "threadhooks"
use "types"
use "units"
use "result"
use "slfill"
use "backtrace"
pkg std =
const startalloctrace : (f : byte[:] -> void)
const endalloctrace : (-> void)
/* null pointers. only used internally. */
pkglocal const Zsliceptr = (0 : byte#)
pkglocal const Align = 16 /* minimum allocation alignment */
pkglocal const align : (m : std.size, align : std.size -> std.size)
pkglocal const allocsz : (sz : std.size -> std.size)
pkglocal const bytealloc : (sz:size -> byte#)
pkglocal const zbytealloc : (sz:size -> byte#)
pkglocal const bytefree : (m:byte#, sz:size -> void)
;;
const Zslab = (0 : slab#)
const Zchunk = (0 : chunk#)
const Slabsz = 4*MiB
const Cachemax = 4
const Bktmax = 128*KiB /* a balance between wasted space and falling back to mmap */
const Pagesz = 4*KiB
var buckets : bucket[32] /* excessive */
var trace : bool
var tracefd : std.fd
type bucket = struct
sz : size /* aligned size */
nper : size /* max number of elements per slab */
slabs : slab# /* partially filled or free slabs */
cache : slab# /* cache of empty slabs, to prevent thrashing */
ncache : size /* size of cache */
;;
type slab = struct
head : byte# /* head of virtual addresses, so we don't leak address space */
next : slab# /* the next slab on the chain */
prev : slab# /* the prev slab on the chain */
freehd : chunk# /* the nodes we're allocating */
nfree : size /* the number of free nodes */
;;
type chunk = struct /* NB: must be smaller than sizeof(slab) */
next : chunk# /* the next chunk in the free list */
;;
const __init__ = {
for var i = 0; i < buckets.len && (Align << i) <= Bktmax; i++
bktinit(&buckets[i], Align << i)
;;
}
const startalloctrace = {path
match openmode(path, Owronly | Ocreat, 0o644)
| `Ok fd: tracefd = fd
| `Err e: -> void
;;
trace = true
}
const endalloctrace = {
std.close(tracefd)
trace = false
}
const zbytealloc = {sz
var p
p = bytealloc(sz)
memfill(p, 0, sz)
-> p
}
const tracealloc = {p, sz
var stk : void#[13] /* [type, addr, sz, 10 stack slots] */
slfill(stk[:], (0 : void#))
stk[0] = (0 : void#)
stk[1] = (p : void#)
stk[2] = (sz : void#)
backtrace(stk[3:])
writealloctrace(stk[:])
}
const tracefree = {p, sz
var stk : void#[3]
stk[0] = (1 : void#)
stk[1] = (p : void#)
stk[2] = (sz : void#)
writealloctrace(stk[:])
}
const writealloctrace = {sl
var len, p
len = sl.len * sizeof(void#)
p = (sl : byte#)
write(tracefd, p[:len])
}
/* Allocates a blob that is 'sz' bytes long. Dies if the allocation fails */
const bytealloc = {sz
var bkt, p
if (sz <= Bktmax)
bkt = &buckets[bktnum(sz)]
lock(memlck)
p = bktalloc(bkt)
unlock(memlck)
else
p = getmem(sz)
if p == Failmem
die("could not get memory\n")
;;
;;
if trace
lock(memlck)
tracealloc(p, sz)
unlock(memlck)
;;
-> p
}
/* frees a blob that is 'sz' bytes long. */
const bytefree = {p, sz
var bkt
if trace
lock(memlck)
tracefree(p, sz)
unlock(memlck)
;;
memfill(p, 0xa8, sz)
if (sz < Bktmax)
bkt = &buckets[bktnum(sz)]
lock(memlck)
bktfree(bkt, p)
unlock(memlck)
else
freemem(p, sz)
;;
}
/* Sets up a single empty bucket */
const bktinit = {b, sz
b.sz = align(sz, Align)
b.nper = (Slabsz - sizeof(slab))/b.sz
b.slabs = Zslab
b.cache = Zslab
b.ncache = 0
}
/* Creates a slab for bucket 'bkt', and fills the chunk list */
const mkslab = {bkt
var p, s
var b, bnext
var off /* offset of chunk head */
if bkt.ncache > 0
s = bkt.cache
bkt.cache = s.next
bkt.ncache--
;;
/*
tricky: we need power of two alignment, so we allocate double the
needed size, chop off the unaligned ends, and waste the address
space. Since the OS is "smart enough", this shouldn't actually
cost us memory, and 64 bits of address space means that we're not
going to have issues with running out of address space for a
while. On a 32 bit system this would be a bad idea.
*/
p = getmem(Slabsz*2)
if p == Failmem
die("Unable to get memory")
;;
s = (align((p : size), Slabsz) : slab#)
s.head = p
s.nfree = bkt.nper
s.next = Zslab
s.prev = Zslab
/* skip past the slab header */
off = align(sizeof(slab), Align)
bnext = nextchunk((s : chunk#), off)
s.freehd = bnext
for var i = 0; i < bkt.nper; i++
b = bnext
bnext = nextchunk(b, bkt.sz)
b.next = bnext
;;
b.next = Zchunk
-> s
}
/*
Allocates a node from bucket 'bkt', crashing if the
allocation cannot be satisfied. Will create a new slab
if there are no slabs on the freelist.
*/
const bktalloc = {bkt
var s
var b
/* find a slab */
s = bkt.slabs
if s == Zslab
s = mkslab(bkt)
bkt.slabs = s
if s == Zslab
die("No memory left")
;;
;;
/* grab the first chunk on the slab */
b = s.freehd
s.freehd = b.next
s.nfree--
if s.nfree == 0
bkt.slabs = s.next
if s.next != Zslab
s.next.prev = Zslab
;;
;;
-> (b : byte#)
}
/*
Frees a chunk of memory 'm' into bucket 'bkt'.
Assumes that the memory already came from a slab
that was created for bucket 'bkt'. Will crash
if this is not the case.
*/
const bktfree = {bkt, m
var s, b
s = (mtrunc(m, Slabsz) : slab#)
b = (m : chunk#)
if s.nfree == 0
if bkt.slabs != Zslab
bkt.slabs.prev = s
;;
s.next = bkt.slabs
s.prev = Zslab
bkt.slabs = s
elif s.nfree == bkt.nper - 1
/*
HACK HACK HACK: if we can't unmap, keep an infinite cache per slab size.
We should solve this better somehow.
*/
if bkt.ncache < Cachemax || !Canunmap
s.next = bkt.cache
s.prev = Zslab
bkt.cache = s
else
/* unlink the slab from the list */
if s.next != Zslab
s.next.prev = s.prev
;;
if s.prev != Zslab
s.prev.next = s.next
;;
if bkt.slabs == s
bkt.slabs = s.next
;;
/* we mapped 2*Slabsz so we could align it,
so we need to unmap the same */
freemem(s.head, Slabsz*2)
;;
-> void
;;
s.nfree++
b.next = s.freehd
s.freehd = b
}
/*
Finds the correct bucket index to allocate from
for allocations of size 'sz'
*/
const bitpos : byte[32] = [
0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
]
const bktnum = {sz
var n, v
v = (sz >> 3 : uint32)
v |= v >> 1
v |= v >> 2
v |= v >> 4
v |= v >> 8
v |= v >> 16
n = bitpos[((v * 0x07c4acdd) & 0xffff_ffffui) >> 27]
-> (n : size)
}
/*
returns the actual size we allocated for a given
size request
*/
const allocsz = {sz
var bktsz
if sz <= Bktmax
bktsz = Align
for var i = 0; bktsz <= Bktmax; i++
if bktsz >= sz
-> bktsz
;;
bktsz *= 2
;;
else
-> align(sz, Pagesz)
;;
die("Size does not match any buckets")
}
/*
aligns a size to a requested alignment.
'align' must be a power of two
*/
const align = {v, align
-> (v + align - 1) & ~(align - 1)
}
/*
chunks are variable sizes, so we can't just
index to get to the next one
*/
const nextchunk = {b, sz : size
-> ((b : intptr) + (sz : intptr) : chunk#)
}
/*
truncates a pointer to 'align'. 'align' must
be a power of two.
*/
const mtrunc = {m, align
-> ((m : intptr) & ~((align : intptr) - 1) : byte#)
}