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Kernel: Remove unnecessary allocation metadata from kmalloc() chunks

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Each allocation header was tracking its index into the chunk bitmap,
but that index can be computed from the allocation address anyway.

Removing this means that each allocation gets 4 more bytes of memory
and this avoids allocating an extra chunk in many cases. :^)
This commit is contained in:
Andreas Kling 2020-02-22 15:09:18 +01:00
parent 99978b771d
commit e334c36757
1 changed files with 19 additions and 20 deletions
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39
Kernel/Heap/kmalloc.cpp
View file

@ -40,10 +40,10 @@
#define SANITIZE_KMALLOC
struct [[gnu::packed]] allocation_t
struct AllocationHeader
{
size_t start;
size_t nchunk;
size_t allocation_size_in_chunks;
u8 data[0];
};
#define BASE_PHYSICAL (0xc0000000 + (4 * MB))
@ -120,8 +120,8 @@ void* kmalloc_impl(size_t size)
Kernel::dump_backtrace();
}
// We need space for the allocation_t structure at the head of the block.
size_t real_size = size + sizeof(allocation_t);
// We need space for the AllocationHeader at the head of the block.
size_t real_size = size + sizeof(AllocationHeader);
if (sum_free < real_size) {
Kernel::dump_backtrace();
@ -153,20 +153,18 @@ void* kmalloc_impl(size_t size)
++chunks_here;
if (chunks_here == chunks_needed) {
auto* a = (allocation_t*)(BASE_PHYSICAL + (first_chunk * CHUNK_SIZE));
u8* ptr = (u8*)a;
ptr += sizeof(allocation_t);
a->nchunk = chunks_needed;
a->start = first_chunk;
auto* a = (AllocationHeader*)(BASE_PHYSICAL + (first_chunk * CHUNK_SIZE));
u8* ptr = a->data;
a->allocation_size_in_chunks = chunks_needed;
for (size_t k = first_chunk; k < (first_chunk + chunks_needed); ++k) {
alloc_map[k / 8] |= 1 << (k % 8);
}
sum_alloc += a->nchunk * CHUNK_SIZE;
sum_free -= a->nchunk * CHUNK_SIZE;
sum_alloc += a->allocation_size_in_chunks * CHUNK_SIZE;
sum_free -= a->allocation_size_in_chunks * CHUNK_SIZE;
#ifdef SANITIZE_KMALLOC
memset(ptr, KMALLOC_SCRUB_BYTE, (a->nchunk * CHUNK_SIZE) - sizeof(allocation_t));
memset(ptr, KMALLOC_SCRUB_BYTE, (a->allocation_size_in_chunks * CHUNK_SIZE) - sizeof(AllocationHeader));
#endif
return ptr;
}
@ -190,16 +188,17 @@ void kfree(void* ptr)
Kernel::InterruptDisabler disabler;
++g_kfree_call_count;
auto* a = (allocation_t*)((((u8*)ptr) - sizeof(allocation_t)));
auto* a = (AllocationHeader*)((((u8*)ptr) - sizeof(AllocationHeader)));
uintptr_t start = ((uintptr_t)a - (uintptr_t)BASE_PHYSICAL) / CHUNK_SIZE;
for (size_t k = a->start; k < (a->start + a->nchunk); ++k)
for (size_t k = start; k < (start + a->allocation_size_in_chunks); ++k)
alloc_map[k / 8] &= ~(1 << (k % 8));
sum_alloc -= a->nchunk * CHUNK_SIZE;
sum_free += a->nchunk * CHUNK_SIZE;
sum_alloc -= a->allocation_size_in_chunks * CHUNK_SIZE;
sum_free += a->allocation_size_in_chunks * CHUNK_SIZE;
#ifdef SANITIZE_KMALLOC
memset(a, KFREE_SCRUB_BYTE, a->nchunk * CHUNK_SIZE);
memset(a, KFREE_SCRUB_BYTE, a->allocation_size_in_chunks * CHUNK_SIZE);
#endif
}
@ -210,8 +209,8 @@ void* krealloc(void* ptr, size_t new_size)
Kernel::InterruptDisabler disabler;
auto* a = (allocation_t*)((((u8*)ptr) - sizeof(allocation_t)));
size_t old_size = a->nchunk * CHUNK_SIZE;
auto* a = (AllocationHeader*)((((u8*)ptr) - sizeof(AllocationHeader)));
size_t old_size = a->allocation_size_in_chunks * CHUNK_SIZE;
if (old_size == new_size)
return ptr;