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chore: clarify m_cs_sz use with mimalloc (#8058)

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We didn't feed correct data to `mi_free_size`, but it turns out it
discards it anyway.
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Sebastian Ullrich 2025-04-23 09:39:01 +02:00 • committed by GitHub
parent dfa72d6c04
commit 2e42013555
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1 changed files with 7 additions and 3 deletions
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10
src/include/lean/lean.h
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@ -116,8 +116,10 @@ reference counting is not needed (== 0). We don't use reference counting for obj
marked as persistent.
For "small" objects stored in compact regions, the field `m_cs_sz` contains the object size. For "small" objects not
stored in compact regions, we use the page information to retrieve its size. This is not an option
with mimalloc, so there we always use `m_cs_sz` (TODO: do everywhere?).
stored in compact regions, we use the page information to retrieve its size so that we can reuse
`m_cs_sz` to store the deletion list inline. Using the page information is not an option with
mimalloc, so there we always use `m_cs_sz`; reusing it for the deletion list is fine in this case as
we do not need the size after an object has been marked for deletion (see `lean_free_small_object`).
During deallocation and 64-bit machines, the fields `m_rc` and `m_cs_sz` store the next object in the deletion TODO list.
These two fields together have 48-bits, and this is enough for modern computers.
@ -421,7 +423,9 @@ static inline void lean_free_small_object(lean_object * o) {
#ifdef LEAN_SMALL_ALLOCATOR
lean_free_small(o);
#elif defined(LEAN_MIMALLOC)
mi_free_size((void *)o, o->m_cs_sz);
// We must NOT use `m_cs_sz` here as it is repurposed for the deletion list; as `mi_free_size`
// is no different from `mi_free` at the time of writing, we don't lose anything from that.
mi_free((void *)o);
#else
size_t* ptr = (size_t*)o - 1;
free_sized(ptr, *ptr + sizeof(size_t));