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Rewrote physical memory allocator

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The physical memory allocator now uses a buddy allocator instead of a stack.

Also moved some of the platform-independent context code to kernel.c.
This commit is contained in:
ngiddings
2022-08-23 13:00:26 -05:00
parent 54e2beefc1
commit bacedbea86
10 changed files with 314 additions and 156 deletions
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251
src/mmgr.c
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@@ -1,5 +1,6 @@
#include "mmgr.h"
#include "string.h"
#include "math.h"
#include "platform/paging.h"
#include "types/status.h"
#include <stdint.h>
@@ -12,11 +13,12 @@
*/
struct page_stack_t
{
/**
* @brief The total number of physical pages managed by the system.
*
*/
size_t total_pages;
unsigned long total_pages;
/**
* @brief Points to the topmost physical address on the stack.
@@ -39,81 +41,230 @@ struct page_stack_t
} page_stack;
int initialize_page_stack(struct memory_map_t *map, physaddr_t *stack_base)
struct page_map_t
{
page_stack.base_pointer = stack_base;
page_stack.limit_pointer = stack_base;
page_stack.stack_pointer = stack_base;
page_stack.total_pages = 0;
for(int i = 0; i < map->size; i++)
/**
* @brief The underlying bitmap representing the availability of chunks of
* physical memory.
*
*/
unsigned long *bitmap;
/**
* @brief The size of the bitmap in bytes.
*
*/
unsigned long bitmap_size;
/**
* @brief The size in bytes of the smallest unit of allocation.
*
* This value should either be the size of a page on the host system, or
* possibly some number of pages.
*
*/
unsigned long block_size;
/**
* @brief
*
*/
unsigned long height;
/**
* @brief The number of available blocks of memory.
*
* Due to memory fragmentation, it may not be possible to allocate all
* available memory at once.
*
*/
unsigned long free_block_count;
} page_map;
const int bitmap_word_size = 8 * sizeof(*page_map.bitmap);
int split_block(int index)
{
if(index)
{
if(map->array[i].type != M_AVAILABLE)
int bitmap_index = index / bitmap_word_size;
int bitmap_offset = index % bitmap_word_size;
page_map.bitmap[bitmap_index] &= ~(1 << bitmap_offset);
index *= 2;
bitmap_index = index / bitmap_word_size;
bitmap_offset = index / bitmap_word_size;
page_map.bitmap[bitmap_index] |= 1 << bitmap_offset;
page_map.bitmap[bitmap_index] |= 1 << (bitmap_offset ^ 1);
}
return index;
}
int find_free_region(int height)
{
if(height > page_map.height || height < 0)
{
return 0;
}
else if(height <= page_map.height - ilog2(bitmap_word_size))
{
for(int index = (1 << (page_map.height - height)) / bitmap_word_size;
index < (1 << (page_map.height - height + 1)) / bitmap_word_size;
index++)
{
continue;
}
size_t location = (map->array[i].location + page_size - 1) & ~(page_size - 1);
while(location + page_size <= map->array[i].location + map->array[i].size)
{
if(free_page(location) != ENONE)
if(page_map.bitmap[index] != 0)
{
return ENOMEM;
return bitmap_word_size * index + __builtin_ctz(page_map.bitmap[index]);
}
page_stack.total_pages++;
location += page_size;
}
}
else
{
static const int bitmasks[] = {0x00000002, 0x0000000C, 0x000000F0, 0x0000FF00, 0xFFFF0000};
int depth = page_map.height - height;
if(page_map.bitmap[0] & bitmasks[depth])
{
return __builtin_ctz(page_map.bitmap[0] & bitmasks[depth]);
}
}
return split_block(find_free_region(height + 1));
}
physaddr_t reserve_region(size_t size)
{
int height = llog2(size / page_map.block_size);
int index = find_free_region(height);
if(index)
{
int bitmap_index = index / bitmap_word_size;
int bitmap_offset = index % bitmap_word_size;
page_map.bitmap[bitmap_index] &= ~(1 << bitmap_offset);
return (page_map.block_size << height) * (index - (1 << (page_map.height - height)));
}
else
{
return ENOMEM;
}
}
int free_region(physaddr_t location, size_t size)
{
int height = llog2(size / page_map.block_size);
int index = (location / (page_map.block_size * (1 << height))) + (1 << (page_map.height - height));
int bitmap_index = index / bitmap_word_size;
int bitmap_offset = index % bitmap_word_size;
page_map.bitmap[bitmap_index] |= 1 << bitmap_offset;
while(page_map.bitmap[bitmap_index] & (1 << (bitmap_offset ^ 1)))
{
page_map.bitmap[bitmap_index] &= ~(1 << bitmap_offset);
page_map.bitmap[bitmap_index] &= ~(1 << (bitmap_offset ^ 1));
index /= 2;
bitmap_index = index / bitmap_word_size;
bitmap_offset = index % bitmap_word_size;
page_map.bitmap[bitmap_index] |= 1 << bitmap_offset;
}
return ENONE;
}
physaddr_t reserve_page()
{
if(page_stack.stack_pointer > page_stack.base_pointer)
{
page_stack.stack_pointer--;
physaddr_t frame = *page_stack.stack_pointer;
*page_stack.stack_pointer = (physaddr_t) 0;
return frame;
}
return ENOMEM;
return reserve_region(page_size);
}
int free_page(physaddr_t location)
{
if(page_stack.stack_pointer < page_stack.limit_pointer)
{
*page_stack.stack_pointer = location;
page_stack.stack_pointer++;
return ENONE;
}
else
{
switch(map_page(page_stack.limit_pointer, location, PAGE_RW))
{
case ENOMEM:
return ENOMEM;
case EOUTOFBOUNDS:
return EOUTOFBOUNDS;
case ENONE:
page_stack.limit_pointer += page_size / sizeof(*page_stack.limit_pointer);
return ENONE;
}
return ENOMEM;
}
return free_region(location, page_size);
}
size_t free_page_count()
{
return page_stack.base_pointer - page_stack.stack_pointer;
return page_map.free_block_count;
}
void *page_stack_bottom()
void *page_map_base()
{
return (void*)page_stack.base_pointer;
return (void*)page_map.bitmap;
}
void *page_stack_top()
void *page_map_end()
{
return (void*)page_stack.limit_pointer;
return (void*)page_map.bitmap + page_map.bitmap_size;
}
enum error_t initialize_page_map(struct memory_map_t *map, void *base, size_t memory_size, unsigned long block_size)
{
// Round memory_size up to nearest power of 2
memory_size = 1 << llog2(memory_size);
page_map.bitmap = (unsigned long*) base;
page_map.bitmap_size = (memory_size / page_size) / 4;
page_map.block_size = block_size;
page_map.height = llog2(memory_size / block_size);
page_map.free_block_count = 0;
int block_log = llog2(block_size);
int pages_mapped = 0;
for(int i = 0; i < map->size; i++)
{
if(map->array[i].type != M_AVAILABLE)
{
continue;
}
physaddr_t location = (map->array[i].location + page_size - 1) & ~(page_size - 1);
physaddr_t region_end = map->array[i].location + map->array[i].size;
while(location + block_size <= region_end)
{
if(pages_mapped < page_map.bitmap_size / page_size)
{
void *page = (void*)page_map.bitmap + pages_mapped * page_size;
for(int level = 0; level < page_table_levels; level++)
{
if(!(get_pte_type(page, level) & PAGE_PRESENT))
{
if(set_pte(page, level, PAGE_PRESENT | PAGE_RW, location))
{
return ENOMEM;
}
else if(level == page_table_levels - 1)
{
pages_mapped++;
}
break;
}
else if(level == page_table_levels - 1)
{
pages_mapped++;
}
}
location += page_size;
continue;
}
int bit_offset = (location / block_size) % bitmap_word_size;
int bitmap_index = (location / block_size) / bitmap_word_size;
size_t chunk_size = (bitmap_word_size - bit_offset) * block_size;
if(bit_offset == 0 && (region_end - location) >= chunk_size)
{
// Set all bits in the word
page_map.bitmap[bitmap_index] = ~0;
}
else if(bit_offset == 0)
{
// Set the first 'count' bits
int count = (region_end - location) >> block_log;
page_map.bitmap[bitmap_index] |= (1 << count) - 1;
}
else if((region_end - location) >= chunk_size)
{
// Set all bits starting at 'bit_offset'
page_map.bitmap[bitmap_index] |= ~((1 << bit_offset) - 1);
}
else
{
// Set all bits starting at 'bit_offset' up to 'count'
int count = (region_end - location) >> block_log;
page_map.bitmap[bitmap_index] |= ((1 << count) - 1) & ~((1 << bit_offset) - 1);
}
location += chunk_size;
}
}
return ENONE;
}
physaddr_t create_address_space()