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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Assertions.h>
#include <AK/Memory.h>
#include <Kernel/Heap/SlabAllocator.h>
#include <Kernel/Heap/kmalloc.h>
#include <Kernel/Sections.h>
#include <Kernel/VM/Region.h>
#define SANITIZE_SLABS
namespace Kernel {
template<size_t templated_slab_size>
class SlabAllocator {
public:
SlabAllocator() = default;
void init(size_t size)
{
m_base = kmalloc_eternal(size);
m_end = (u8*)m_base + size;
FreeSlab* slabs = (FreeSlab*)m_base;
m_slab_count = size / templated_slab_size;
for (size_t i = 1; i < m_slab_count; ++i) {
slabs[i].next = &slabs[i - 1];
}
slabs[0].next = nullptr;
m_freelist = &slabs[m_slab_count - 1];
m_num_allocated = 0;
}
constexpr size_t slab_size() const { return templated_slab_size; }
size_t slab_count() const { return m_slab_count; }
void* alloc()
{
FreeSlab* free_slab;
{
// We want to avoid being swapped out in the middle of this
ScopedCritical critical;
FreeSlab* next_free;
free_slab = m_freelist.load(AK::memory_order_consume);
do {
if (!free_slab)
return kmalloc(slab_size());
// It's possible another processor is doing the same thing at
// the same time, so next_free *can* be a bogus pointer. However,
// in that case compare_exchange_strong would fail and we would
// try again.
next_free = free_slab->next;
} while (!m_freelist.compare_exchange_strong(free_slab, next_free, AK::memory_order_acq_rel));
m_num_allocated++;
}
#ifdef SANITIZE_SLABS
memset(free_slab, SLAB_ALLOC_SCRUB_BYTE, slab_size());
#endif
return free_slab;
}
void dealloc(void* ptr)
{
VERIFY(ptr);
if (ptr < m_base || ptr >= m_end) {
kfree(ptr);
return;
}
FreeSlab* free_slab = (FreeSlab*)ptr;
#ifdef SANITIZE_SLABS
if (slab_size() > sizeof(FreeSlab*))
memset(free_slab->padding, SLAB_DEALLOC_SCRUB_BYTE, sizeof(FreeSlab::padding));
#endif
// We want to avoid being swapped out in the middle of this
ScopedCritical critical;
FreeSlab* next_free = m_freelist.load(AK::memory_order_consume);
do {
free_slab->next = next_free;
} while (!m_freelist.compare_exchange_strong(next_free, free_slab, AK::memory_order_acq_rel));
m_num_allocated--;
}
size_t num_allocated() const { return m_num_allocated; }
size_t num_free() const { return m_slab_count - m_num_allocated; }
private:
struct FreeSlab {
FreeSlab* next;
char padding[templated_slab_size - sizeof(FreeSlab*)];
};
Atomic<FreeSlab*> m_freelist { nullptr };
Atomic<size_t, AK::MemoryOrder::memory_order_relaxed> m_num_allocated;
size_t m_slab_count;
void* m_base { nullptr };
void* m_end { nullptr };
static_assert(sizeof(FreeSlab) == templated_slab_size);
};
static SlabAllocator<16> s_slab_allocator_16;
static SlabAllocator<32> s_slab_allocator_32;
static SlabAllocator<64> s_slab_allocator_64;
static SlabAllocator<128> s_slab_allocator_128;
static SlabAllocator<256> s_slab_allocator_256;
#if ARCH(I386)
static_assert(sizeof(Region) <= s_slab_allocator_128.slab_size());
#endif
template<typename Callback>
void for_each_allocator(Callback callback)
{
callback(s_slab_allocator_16);
callback(s_slab_allocator_32);
callback(s_slab_allocator_64);
callback(s_slab_allocator_128);
callback(s_slab_allocator_256);
}
UNMAP_AFTER_INIT void slab_alloc_init()
{
s_slab_allocator_16.init(128 * KiB);
s_slab_allocator_32.init(128 * KiB);
s_slab_allocator_64.init(512 * KiB);
s_slab_allocator_128.init(512 * KiB);
s_slab_allocator_256.init(128 * KiB);
}
void* slab_alloc(size_t slab_size)
{
if (slab_size <= 16)
return s_slab_allocator_16.alloc();
if (slab_size <= 32)
return s_slab_allocator_32.alloc();
if (slab_size <= 64)
return s_slab_allocator_64.alloc();
if (slab_size <= 128)
return s_slab_allocator_128.alloc();
if (slab_size <= 256)
return s_slab_allocator_256.alloc();
VERIFY_NOT_REACHED();
}
void slab_dealloc(void* ptr, size_t slab_size)
{
if (slab_size <= 16)
return s_slab_allocator_16.dealloc(ptr);
if (slab_size <= 32)
return s_slab_allocator_32.dealloc(ptr);
if (slab_size <= 64)
return s_slab_allocator_64.dealloc(ptr);
if (slab_size <= 128)
return s_slab_allocator_128.dealloc(ptr);
if (slab_size <= 256)
return s_slab_allocator_256.dealloc(ptr);
VERIFY_NOT_REACHED();
}
void slab_alloc_stats(Function<void(size_t slab_size, size_t allocated, size_t free)> callback)
{
for_each_allocator([&](auto& allocator) {
auto num_allocated = allocator.num_allocated();
auto num_free = allocator.slab_count() - num_allocated;
callback(allocator.slab_size(), num_allocated, num_free);
});
}
}
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