f0e2ab702a
# Pagemap The Pagemap now stores all the meta-data for the object allocation. The meta-data in the pagemap is effectively a triple of the sizeclass, the remote allocator, and a pointer to a 64 byte block of meta-data for this chunk of memory. By storing the pointer to a block, it allows the pagemap to handle multiple slab sizes without branching on the fast path. There is one entry in the pagemap per 16KiB of address space, but by using the same entry in the pagemap for 4 adjacent entries, then we can treat a 64KiB range can be treated as a single slab of allocations. This change also means there is almost no capability amplification required by the implementation on CHERI for finding meta-data. The only amplification is required, when we change the way a chunk is used to a size of object allocation. # Backend There is a second major aspect of the refactor that there is now a narrow API that abstracts the Pagemap, PAL and address space management. This should better enable the compartmentalisation and makes it easier to produce alternative backends for various research directions. This is a template parameter that can be used to specialised by the front-end in different ways. # Thread local state The thread local state has been refactored into two components, one (called 'localalloc') that is stored directly in the TLS and is constant initialised, and one that is allocated in the address space (called 'coreallloc') which is lazily created and pooled. # Difference This removes Superslabs/Medium slabs as there meta-data is now part of the pagemap.
110 lines
2.7 KiB
C++
110 lines
2.7 KiB
C++
#pragma once
|
|
|
|
#include "../ds/flaglock.h"
|
|
#include "../ds/mpmcstack.h"
|
|
#include "../pal/pal_concept.h"
|
|
#include "pooled.h"
|
|
|
|
namespace snmalloc
|
|
{
|
|
/**
|
|
* Pool of a particular type of object.
|
|
*
|
|
* This pool will never return objects to the OS. It maintains a list of all
|
|
* objects ever allocated that can be iterated (not concurrency safe). Pooled
|
|
* types can be acquired from the pool, and released back to the pool. This is
|
|
* concurrency safe.
|
|
*
|
|
* This is used to bootstrap the allocation of allocators.
|
|
*/
|
|
template<class T>
|
|
class PoolState
|
|
{
|
|
template<typename TT>
|
|
friend class Pool;
|
|
|
|
private:
|
|
std::atomic_flag lock = ATOMIC_FLAG_INIT;
|
|
MPMCStack<T, PreZeroed> stack;
|
|
T* list{nullptr};
|
|
|
|
public:
|
|
constexpr PoolState() = default;
|
|
};
|
|
|
|
template<typename T>
|
|
class Pool
|
|
{
|
|
public:
|
|
template<typename SharedStateHandle, typename... Args>
|
|
static T* acquire(SharedStateHandle h, Args&&... args)
|
|
{
|
|
PoolState<T>& pool = h.pool();
|
|
T* p = pool.stack.pop();
|
|
|
|
if (p != nullptr)
|
|
{
|
|
p->set_in_use();
|
|
return p;
|
|
}
|
|
|
|
p = ChunkAllocator::alloc_meta_data<T>(
|
|
h, nullptr, std::forward<Args>(args)...);
|
|
|
|
FlagLock f(pool.lock);
|
|
p->list_next = pool.list;
|
|
pool.list = p;
|
|
|
|
p->set_in_use();
|
|
return p;
|
|
}
|
|
|
|
/**
|
|
* Return to the pool an object previously retrieved by `acquire`
|
|
*
|
|
* Do not return objects from `extract`.
|
|
*/
|
|
template<typename SharedStateHandle>
|
|
static void release(SharedStateHandle h, T* p)
|
|
{
|
|
// The object's destructor is not run. If the object is "reallocated", it
|
|
// is returned without the constructor being run, so the object is reused
|
|
// without re-initialisation.
|
|
p->reset_in_use();
|
|
h.pool().stack.push(p);
|
|
}
|
|
|
|
template<typename SharedStateHandle>
|
|
static T* extract(SharedStateHandle h, T* p = nullptr)
|
|
{
|
|
// Returns a linked list of all objects in the stack, emptying the stack.
|
|
if (p == nullptr)
|
|
return h.pool().stack.pop_all();
|
|
|
|
return p->next;
|
|
}
|
|
|
|
/**
|
|
* Return to the pool a list of object previously retrieved by `extract`
|
|
*
|
|
* Do not return objects from `acquire`.
|
|
*/
|
|
template<typename SharedStateHandle>
|
|
static void restore(SharedStateHandle h, T* first, T* last)
|
|
{
|
|
// Pushes a linked list of objects onto the stack. Use to put a linked
|
|
// list returned by extract back onto the stack.
|
|
h.pool().stack.push(first, last);
|
|
}
|
|
|
|
template<typename SharedStateHandle>
|
|
static T* iterate(SharedStateHandle h, T* p = nullptr)
|
|
{
|
|
if (p == nullptr)
|
|
return h.pool().list;
|
|
|
|
return p->list_next;
|
|
}
|
|
};
|
|
} // namespace snmalloc
|