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Kernel: Remove the kmalloc_eternal heap :^)

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This was a premature optimization from the early days of SerenityOS.
The eternal heap was a simple bump pointer allocator over a static
byte array. My original idea was to avoid heap fragmentation and improve
data locality, but both ideas were rooted in cargo culting, not data.

We would reserve 4 MiB at boot and only ended up using ~256 KiB, wasting
the rest.

This patch replaces all kmalloc_eternal() usage by regular kmalloc().
This commit is contained in:
Andreas Kling 2021-12-28 19:12:22 +01:00
parent a1be135891
commit ac7ce12123
46 changed files with 5 additions and 82 deletions
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25
Kernel/Heap/kmalloc.cpp
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@ -29,7 +29,6 @@ static constexpr size_t CHUNK_SIZE = 64;
#endif
#define POOL_SIZE (2 * MiB)
#define ETERNAL_RANGE_SIZE (4 * MiB)
namespace std {
const nothrow_t nothrow;
@ -307,18 +306,13 @@ READONLY_AFTER_INIT static KmallocGlobalData* g_kmalloc_global;
alignas(KmallocGlobalData) static u8 g_kmalloc_global_heap[sizeof(KmallocGlobalData)];
// Treat the heap as logically separate from .bss
__attribute__((section(".heap"))) static u8 kmalloc_eternal_heap[ETERNAL_RANGE_SIZE];
__attribute__((section(".heap"))) static u8 kmalloc_pool_heap[POOL_SIZE];
static size_t g_kmalloc_bytes_eternal = 0;
static size_t g_kmalloc_call_count;
static size_t g_kfree_call_count;
static size_t g_nested_kfree_calls;
bool g_dump_kmalloc_stacks;
static u8* s_next_eternal_ptr;
READONLY_AFTER_INIT static u8* s_end_of_eternal_range;
void kmalloc_enable_expand()
{
g_kmalloc_global->enable_expansion();
@ -335,28 +329,10 @@ static inline void kmalloc_verify_nospinlock_held()
UNMAP_AFTER_INIT void kmalloc_init()
{
// Zero out heap since it's placed after end_of_kernel_bss.
memset(kmalloc_eternal_heap, 0, sizeof(kmalloc_eternal_heap));
memset(kmalloc_pool_heap, 0, sizeof(kmalloc_pool_heap));
g_kmalloc_global = new (g_kmalloc_global_heap) KmallocGlobalData(kmalloc_pool_heap, sizeof(kmalloc_pool_heap));
s_lock.initialize();
s_next_eternal_ptr = kmalloc_eternal_heap;
s_end_of_eternal_range = s_next_eternal_ptr + sizeof(kmalloc_eternal_heap);
}
void* kmalloc_eternal(size_t size)
{
kmalloc_verify_nospinlock_held();
size = round_up_to_power_of_two(size, sizeof(void*));
SpinlockLocker lock(s_lock);
void* ptr = s_next_eternal_ptr;
s_next_eternal_ptr += size;
VERIFY(s_next_eternal_ptr < s_end_of_eternal_range);
g_kmalloc_bytes_eternal += size;
return ptr;
}
void* kmalloc(size_t size)
@ -493,7 +469,6 @@ void get_kmalloc_stats(kmalloc_stats& stats)
SpinlockLocker lock(s_lock);
stats.bytes_allocated = g_kmalloc_global->allocated_bytes();
stats.bytes_free = g_kmalloc_global->free_bytes();
stats.bytes_eternal = g_kmalloc_bytes_eternal;
stats.kmalloc_call_count = g_kmalloc_call_count;
stats.kfree_call_count = g_kfree_call_count;
}