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xo-alloc: bugfix expand: limit_ is soft, hi_ is hard. + docs

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This commit is contained in:
Roland Conybeare 2025-11-23 11:35:05 -05:00
commit 40128c423c
2 changed files with 30 additions and 3 deletions
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6
include/xo/alloc/ArenaAlloc.hpp
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@ -127,7 +127,7 @@ namespace xo {
bool debug_flag);
/** size of virtual address range reserved for this allocator **/
std::size_t reserved() const { return this->size(); }
std::size_t reserved() const { return hi_ - lo_; };
std::size_t page_size() const { return page_z_; }
std::byte * free_ptr() const { return free_ptr_; }
@ -212,7 +212,9 @@ namespace xo {
std::byte * checkpoint_ = nullptr;
/** free pointer. memory in range [@ref free_, @ref limit_) available **/
std::byte * free_ptr_ = nullptr;
/** soft limit: end of committed virtual memory **/
/** soft limit: end of committed virtual memory
* invariant: @ref limit_ = @ref lo_ + @ref committed_z_
**/
std::byte * limit_ = nullptr;
/** hard limit: end of reserved virtual memory **/
std::byte * hi_ = nullptr;

27
src/alloc/ArenaAlloc.cpp
View file

@ -170,15 +170,37 @@ namespace xo {
return true;
}
if (lo_ + offset_z > limit_) {
if (lo_ + offset_z > hi_) {
throw std::runtime_error(tostr("ArenaAlloc::expand: requested size exceeds reserved size",
xtag("requested", offset_z), xtag("reserved", reserved())));
}
/*
* pre:
*
* _______________...................................
* ^ ^ ^
* lo limit hi
*
* < committed_z >
* <----------offset_z----------->
* > <- z: 0 <= z < hugepage_z
* <---------aligned_offset_z--------->
* <--- add_commit_z -->
*
* post:
* ____________________________________..............
* ^ ^ ^
* lo limit hi
*
*/
std::size_t aligned_offset_z = align_lub(offset_z, hugepage_z_);
std::byte * commit_start = lo_ + committed_z_;
std::size_t add_commit_z = aligned_offset_z - committed_z_;
assert(limit_ == lo_ + committed_z_);
log && log(xtag("aligned_offset_z", aligned_offset_z),
xtag("add_commit_z", add_commit_z));
@ -196,6 +218,9 @@ namespace xo {
this->committed_z_ = aligned_offset_z;
this->limit_ = this->lo_ + committed_z_;
assert(committed_z_ % hugepage_z_ == 0);
assert(reinterpret_cast<size_t>(limit_) % hugepage_z_ == 0);
return true;
}