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xo-alloc2: refactor: consolidate alloc methods into DArena

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This commit is contained in:
Roland Conybeare 2025-12-18 18:54:01 -05:00
commit 5314c12242
4 changed files with 289 additions and 233 deletions
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40
xo-alloc2/include/xo/alloc2/arena/DArena.hpp
View file

@ -44,6 +44,14 @@ namespace xo {
/** @brief type for allocation header (if enabled) **/
using header_type = AllocHeader; //std::uint64_t;
/** @brief mode argument for @ref _alloc **/
enum class alloc_mode : uint8_t {
standard,
super,
sub_incomplete,
sub_complete,
};
///@}
/** @defgroup mm-arena-ctors arena constructors and destructors **/
@ -107,10 +115,42 @@ namespace xo {
**/
AllocInfo alloc_info(value_type mem) const noexcept;
/** allocate at least @p z bytes of memory.
* Return nullptr and capture error if unable to satisfy request.
* May expand committed memory, as long as resulting committed size
* is no larger than reserved size
**/
value_type alloc(size_type z);
/** when store_header_flag enabled:
* like alloc(), but combine memory consumed by this alloc
* plus following consecutive sub_alloc()'s into a single header.
* otherwise equivalent to alloc()
**/
value_type super_alloc(size_type z);
/** when store_header_flag enabled:
* follow preceding super_alloc() by one or more sub_allocs().
* accumulate total allocated size (including padding) into
* single header. All sub_allocs() except the last must set
* @p complete_flag to false. The last sub_alloc() must set
* @p complete_flag to true.
**/
value_type sub_alloc(size_type z, bool complete_flag);
/** capture error information: advance error count + set last_error **/
void capture_error(error err,
size_type target_z = 0) const;
/** alloc driver. shared by alloc(), super_alloc(), sub_alloc() **/
value_type _alloc(std::size_t req_z, alloc_mode mode);
/** expand committed space in arena @p d
* to size at least @p z
* In practice will round up to a multiple of @ref page_z_.
**/
bool expand(size_type z) noexcept;
/** discard all allocated memory, return to empty state
* Promise:
* - committed memory unchanged

9
xo-alloc2/include/xo/alloc2/arena/IAllocator_DArena.hpp
View file

@ -34,13 +34,6 @@ namespace xo {
using range_type = std::pair<obj<AAllocIterator>,
obj<AAllocIterator>>;
enum class alloc_mode : uint8_t {
standard,
super,
sub_incomplete,
sub_complete,
};
static std::string_view name(const DArena &) noexcept;
static size_type reserved(const DArena &) noexcept;
static size_type size(const DArena &) noexcept;
@ -84,7 +77,7 @@ namespace xo {
/** alloc driver. shared by alloc(), super_alloc(), sub_alloc() **/
static value_type _alloc(DArena &,
size_type z,
alloc_mode mode);
DArena::alloc_mode mode);
};
// template <>

242
xo-alloc2/src/alloc2/DArena.cpp
View file

@ -7,6 +7,7 @@
#include "arena/DArena.hpp"
#include "arena/DArenaIterator.hpp"
#include "xo/alloc2/padding.hpp"
#include "xo/indentlog/scope.hpp"
#include "xo/indentlog/print/tag.hpp"
#include <cassert>
#include <sys/mman.h> // for ::munmap()
@ -289,6 +290,47 @@ namespace xo {
return DArenaIterator::end(this);
}
std::byte *
DArena::alloc(std::size_t req_z)
{
/* - primary allocation path:
* exactly 1 header per alloc() call.
* - store_header_flag follows configuration
*/
return _alloc(req_z, alloc_mode::standard);
}
std::byte *
DArena::super_alloc(std::size_t req_z)
{
/* - (uncommon) pattern for parent alloc immediately followed by
* zero-or-more susidiary allocs, all sharing a single header.
* - collapses into alloc() behavior when
* ArenaConfig.store_header_flag_ disabled
*/
return _alloc(req_z,
alloc_mode::super);
}
std::byte *
DArena::sub_alloc(std::size_t req_z,
bool complete_flag)
{
/* - (uncommon) pattern for subsidiary allocs:
* that piggyback onto preceding super_alloc()
* - collapses into alloc() behavior when
* ArenaConfig.store_header_flag_ disabled
*/
return _alloc(req_z,
(complete_flag
? alloc_mode::sub_complete
: alloc_mode::sub_incomplete));
}
void
DArena::capture_error(error err,
size_type target_z) const
@ -303,6 +345,206 @@ namespace xo {
reserved());
}
byte *
DArena::_alloc(std::size_t req_z, alloc_mode mode)
{
scope log(XO_DEBUG(config_.debug_flag_));
/*
* sub_complete
* sub_incomplete |
* standard super | |
* v v v v
*/
std::array<bool, 4> store_header_v = {{ true, true, false, false }};
std::array<bool, 4> retain_header_v = {{ false, true, false, false }};
std::array<bool, 4> store_guard_v = {{ true, false, false, true }};
/* -> write header at free_ */
bool store_header_flag = false;
/* -> stash last_header_*/
bool retain_header_flag = false;
/* -> write guard bytes */
bool store_guard = false;
if (config_.store_header_flag_) {
store_header_flag = store_header_v[(int)mode];
retain_header_flag = retain_header_v[(int)mode];
store_guard = store_guard_v[(int)mode];
}
assert(padding::is_aligned((size_t)free_));
/*
* free_(pre)
* v
*
* <-------------z1--------------->
* < guard >< hz >< req_z >< dz >< guard >
*
* used <== +++++++++0000zzzz@@@@@@@@@@@@@@@@@ppppppp+++++++++ ==> avail
*
* ^ ^ ^
* header mem |
* ^ |
* last_header_ free_(post)
*
* [+] guard after each allocation, for simple sanitize checks
* [0] unused header bits (avail to application)
* [z] record allocation size
* [@] new allocated memory
* [p] padding (to uintptr_t alignment)
*/
/* non-zero if header feature enabled */
size_t hz = 0;
/* dz: pad req_z to alignment size (multiple of 8 bytes, probably) */
size_t dz = padding::alloc_padding(req_z);
size_t z0 = req_z + dz;
/* if non-zero:
* will store padded alloc size at the beginning of each allocation
* reminder:
* important to store padded size for correct arena iteration
*/
uint64_t header = req_z + dz;
if (store_header_flag)
{
if (config_.header_.is_size_enabled()) [[likely]] {
hz = sizeof(header);
} else {
/* req_z doesn't fit in configured header_size_mask bits */
capture_error(error::header_size_mask);
return nullptr;
}
}
size_t z1 = hz + z0;
assert(padding::is_aligned(z1));
if (!this->expand(this->allocated() + z1)) [[unlikely]] {
/* (error state already captured) */
return nullptr;
}
if (store_header_flag) {
/* capturing header */
*(uint64_t *)free_ = header;
if (retain_header_flag) {
/* and rembering for subsequent
* sub_alloc()
*/
last_header_ = (AllocHeader *)free_;
}
}
byte * mem = free_ + hz;
this->free_ += z1;
if (store_guard) {
/* write guard bytes for overrun detection */
::memset(free_,
config_.header_.guard_byte_,
config_.header_.guard_z_);
this->free_ += config_.header_.guard_z_;
}
log && log(xtag("self", config_.name_),
xtag("hz", hz),
xtag("z0", req_z),
xtag("+pad", dz),
xtag("z1", z1),
xtag("size", this->committed()),
xtag("avail", this->available()));
log && log(xtag("mem", mem),
xtag("free", free_));
return mem;
}
bool
DArena::expand(size_t target_z) noexcept
{
scope log(XO_DEBUG(config_.debug_flag_),
xtag("target_z", target_z),
xtag("committed_z", committed_z_));
if (target_z <= committed_z_) [[likely]] {
log && log("trivial success, offset within committed range",
xtag("target_z", target_z),
xtag("committed_z", committed_z_));
return true;
}
if (lo_ + target_z > hi_) [[unlikely]] {
this->capture_error(error::reserve_exhausted, target_z);
return false;
}
/*
* pre:
*
* _______________...................................
* ^ ^ ^
* lo limit hi
*
* < committed_z >
* <----------target_z----------->
* > <- z: 0 <= z < hugepage_z
* <---------aligned_target_z--------->
* <--- add_commit_z -->
*
* post:
* ____________________________________..............
* ^ ^ ^
* lo limit hi
*
*/
std::size_t aligned_target_z = padding::with_padding(target_z, config_.hugepage_z_);
std::byte * commit_start = limit_; // = lo_ + committed_z_;
std::size_t add_commit_z = aligned_target_z - committed_z_;
assert(limit_ == lo_ + committed_z_);
// log && log(xtag("aligned_offset_z", aligned_offset_z),
// xtag("add_commit_z", add_commit_z));
// log && log("expand committed range",
// xtag("commit_start", commit_start),
// xtag("add_commit_z", add_commit_z),
// xtag("commit_end", commit_start + add_commit_z));
if (::mprotect(commit_start,
add_commit_z,
PROT_READ | PROT_WRITE) != 0) [[unlikely]]
{
capture_error(error::commit_failed, add_commit_z);
return false;
}
committed_z_ = aligned_target_z;
limit_ = lo_ + committed_z_;
if (commit_start == lo_) [[unlikely]] {
/* first expand() for this allocator - start with guard_z_ bytes */
::memset(free_,
config_.header_.guard_byte_,
config_.header_.guard_z_);
free_ += config_.header_.guard_z_;
}
assert(committed_z_ % config_.hugepage_z_ == 0);
assert(reinterpret_cast<size_t>(limit_) % config_.hugepage_z_ == 0);
return true;
} /*expand*/
void
DArena::clear() noexcept
{

231
xo-alloc2/src/alloc2/IAllocator_DArena.cpp
View file

@ -70,14 +70,6 @@ namespace xo {
return s.alloc_info(mem);
}
void dummy(const DArena & s) {
byte * begin_mem = nullptr;
DArenaIterator * ix = new (begin_mem) DArenaIterator(&s, DArenaIterator::begin_header(&s));
obj<AAllocIterator,DArenaIterator> ix_vt{ix};
}
auto
IAllocator_DArena::alloc_range(const DArena & s,
DArena & ialloc) noexcept -> range_type
@ -102,107 +94,21 @@ namespace xo {
bool
IAllocator_DArena::expand(DArena & s, size_t target_z) noexcept
{
scope log(XO_DEBUG(s.config_.debug_flag_),
xtag("target_z", target_z),
xtag("committed_z", s.committed_z_));
if (target_z <= s.committed_z_) [[likely]] {
log && log("trivial success, offset within committed range",
xtag("target_z", target_z),
xtag("committed_z", s.committed_z_));
return true;
}
if (s.lo_ + target_z > s.hi_) [[unlikely]] {
s.capture_error(error::reserve_exhausted, target_z);
return false;
}
/*
* pre:
*
* _______________...................................
* ^ ^ ^
* lo limit hi
*
* < committed_z >
* <----------target_z----------->
* > <- z: 0 <= z < hugepage_z
* <---------aligned_target_z--------->
* <--- add_commit_z -->
*
* post:
* ____________________________________..............
* ^ ^ ^
* lo limit hi
*
*/
std::size_t aligned_target_z = padding::with_padding(target_z, s.config_.hugepage_z_);
std::byte * commit_start = s.limit_; // = s.lo_ + s.committed_z_;
std::size_t add_commit_z = aligned_target_z - s.committed_z_;
assert(s.limit_ == s.lo_ + s.committed_z_);
// log && log(xtag("aligned_offset_z", aligned_offset_z),
// xtag("add_commit_z", add_commit_z));
// log && log("expand committed range",
// xtag("commit_start", commit_start),
// xtag("add_commit_z", add_commit_z),
// xtag("commit_end", commit_start + add_commit_z));
if (::mprotect(commit_start,
add_commit_z,
PROT_READ | PROT_WRITE) != 0) [[unlikely]]
{
s.capture_error(error::commit_failed, add_commit_z);
return false;
}
s.committed_z_ = aligned_target_z;
s.limit_ = s.lo_ + s.committed_z_;
if (commit_start == s.lo_) [[unlikely]] {
/* first expand() for this allocator - start with guard_z_ bytes */
::memset(s.free_,
s.config_.header_.guard_byte_,
s.config_.header_.guard_z_);
s.free_ += s.config_.header_.guard_z_;
}
assert(s.committed_z_ % s.config_.hugepage_z_ == 0);
assert(reinterpret_cast<size_t>(s.limit_) % s.config_.hugepage_z_ == 0);
return true;
return s.expand(target_z);
} /*expand*/
std::byte *
IAllocator_DArena::alloc(DArena & s,
std::size_t req_z)
{
/* - primary allocation path:
* exactly 1 header per alloc() call.
* - store_header_flag follows configuration
*/
return _alloc(s, req_z,
alloc_mode::standard);
return s.alloc(req_z);
}
std::byte *
IAllocator_DArena::super_alloc(DArena & s,
std::size_t req_z)
{
/* - (uncommon) pattern for parent alloc immediately followed by
* zero-or-more susidiary allocs, all sharing a single header.
* - collapses into alloc() behavior when
* ArenaConfig.store_header_flag_ disabled
*/
return _alloc(s, req_z,
alloc_mode::super);
return s.super_alloc(req_z);
}
std::byte *
@ -210,140 +116,15 @@ namespace xo {
std::size_t req_z,
bool complete_flag)
{
/* - (uncommon) pattern for subsidiary allocs:
* that piggyback onto preceding super_alloc()
* - collapses into alloc() behavior when
* ArenaConfig.store_header_flag_ disabled
*/
return _alloc(s, req_z,
(complete_flag
? alloc_mode::sub_complete
: alloc_mode::sub_incomplete));
return s.sub_alloc(req_z, complete_flag);
}
byte *
IAllocator_DArena::_alloc(DArena & s,
std::size_t req_z,
alloc_mode mode)
DArena::alloc_mode mode)
{
scope log(XO_DEBUG(s.config_.debug_flag_));
/*
* sub_complete
* sub_incomplete |
* standard super | |
* v v v v
*/
std::array<bool, 4> store_header_v = {{ true, true, false, false }};
std::array<bool, 4> retain_header_v = {{ false, true, false, false }};
std::array<bool, 4> store_guard_v = {{ true, false, false, true }};
/* -> write header at s.free_ */
bool store_header_flag = false;
/* -> stash s.last_header_*/
bool retain_header_flag = false;
/* -> write guard bytes */
bool store_guard = false;
if (s.config_.store_header_flag_) {
store_header_flag = store_header_v[(int)mode];
retain_header_flag = retain_header_v[(int)mode];
store_guard = store_guard_v[(int)mode];
}
assert(padding::is_aligned((size_t)s.free_));
/*
* free_(pre)
* v
*
* <-------------z1--------------->
* < guard >< hz >< req_z >< dz >< guard >
*
* used <== +++++++++0000zzzz@@@@@@@@@@@@@@@@@ppppppp+++++++++ ==> avail
*
* ^ ^ ^
* header mem |
* ^ |
* last_header_ free_(post)
*
* [+] guard after each allocation, for simple sanitize checks
* [0] unused header bits (avail to application)
* [z] record allocation size
* [@] new allocated memory
* [p] padding (to uintptr_t alignment)
*/
/* non-zero if header feature enabled */
size_t hz = 0;
/* dz: pad req_z to alignment size (multiple of 8 bytes, probably) */
size_t dz = padding::alloc_padding(req_z);
size_t z0 = req_z + dz;
/* if non-zero:
* will store padded alloc size at the beginning of each allocation
* reminder:
* important to store padded size for correct arena iteration
*/
uint64_t header = req_z + dz;
if (store_header_flag)
{
if (s.config_.header_.is_size_enabled()) [[likely]] {
hz = sizeof(header);
} else {
/* req_z doesn't fit in configured header_size_mask bits */
s.capture_error(error::header_size_mask);
return nullptr;
}
}
size_t z1 = hz + z0;
assert(padding::is_aligned(z1));
if (!expand(s, allocated(s) + z1)) [[unlikely]] {
/* (error state already captured) */
return nullptr;
}
if (store_header_flag) {
/* capturing header */
*(uint64_t *)s.free_ = header;
if (retain_header_flag) {
/* and rembering for subsequent
* sub_alloc()
*/
s.last_header_ = (AllocHeader *)s.free_;
}
}
byte * mem = s.free_ + hz;
s.free_ += z1;
if (store_guard) {
/* write guard bytes for overrun detection */
::memset(s.free_,
s.config_.header_.guard_byte_,
s.config_.header_.guard_z_);
s.free_ += s.config_.header_.guard_z_;
}
log && log(xtag("self", s.config_.name_),
xtag("hz", hz),
xtag("z0", req_z),
xtag("+pad", dz),
xtag("z1", z1),
xtag("size", size(s)),
xtag("avail", available(s)));
log && log(xtag("mem", mem),
xtag("free", s.free_));
return mem;
return s._alloc(req_z, mode);
}
void