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xo-arena: + DArena methods {checkpoint, restore}

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This commit is contained in:
Roland Conybeare 2026-01-18 19:17:54 -05:00
commit 64b165766f
1 changed files with 16 additions and 29 deletions
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45
xo-arena/include/xo/arena/DArena.hpp
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@ -62,6 +62,12 @@ namespace xo {
sub_complete,
};
/** @brief Checkpoint for unwinding arena state **/
struct Checkpoint {
explicit Checkpoint(std::byte * x) : free_{x} {}
std::byte * free_;
};
///@}
/** @defgroup mm-arena-ctors arena constructors and destructors **/
@ -115,34 +121,6 @@ namespace xo {
**/
bool contains(const void * addr) const noexcept { return (lo_ <= addr) && (addr < hi_); }
#ifdef OBSOLETE
/** obtain uncommitted contiguous memory range comprising
* a whole multiple of @p align_z bytes, of at least size @p req_z,
* aligned on a @p align_z boundary. Uncommitted memory is not (yet)
* backed by physical memory.
*
* If @p enable_hugepage_flag is true and THP
* (transparent huge pages) are available, use THP for arena memory.
* This relieves TLB and page table memory when @p req_z is a lot larger than
* page size (likely 4KB). Cost is that arena will consum physical memory in unit
* of @p align_z. Arena may waste up to @p align_z bytes of memory as a result.
*
* If @p enable_hugepage_flag is true, @p align_z should be huge page size
* (probably 2MB) for optimal performance.
*
* At present the THP feature is not supported on OSX.
* May be supportable through mach_vm_allocate().
*
* Note that we reject MAP_HUGETLB|MAP_HUGE_2MB flags to mmap here,
* since requires previously-reserved memory in /proc/sys/vm/nr_hugepages.
*
* @return pair giving reserved memory address range [lo,hi)
**/
static range_type map_aligned_range(size_type req_z,
size_type align_z,
bool enable_hugepage_flag);
#endif
/** true if arena is mapped i.e. has a reserved address range **/
bool is_mapped() const noexcept { return (lo_ != nullptr) && (hi_ != nullptr); }
@ -165,7 +143,8 @@ namespace xo {
*
* Require:
* 1. @p mem is address returned by allocation on this arena
* i.e. by @ref IAllocator_DArena::alloc() or @ref IAllocator_DArena::alloc_super()
* i.e. by @ref IAllocator_DArena::alloc() or
* @ref IAllocator_DArena::alloc_super()
* 2. @p mem has not been invalidated since it was allocated
* i.e. by call to @ref DArena::clear
*
@ -218,6 +197,14 @@ namespace xo {
/** create initial guard **/
void establish_initial_guard() noexcept;
/** checkpoint arena state. Revert to the same state with
* @ref rstore
**/
Checkpoint checkpoint() noexcept { return Checkpoint(free_); }
/** restore arena state to previously-established checkpoint **/
void restore(Checkpoint ckp) noexcept { free_ = ckp.free_; }
/** discard all allocated memory, return to empty state
* Promise:
* - committed memory unchanged