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379 lines
11 KiB
C
379 lines
11 KiB
C
/* See the end of this file for copyright and license terms. */
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#include <arch/page.h>
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#include <gay/bits.h>
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#include <gay/clist.h>
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#include <gay/config.h>
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#include <gay/kprintf.h>
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#include <gay/mm.h>
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#include <gay/mutex.h>
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#include <gay/types.h>
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#include <gay/util.h>
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#include <limits.h>
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#include <string.h>
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#ifndef __HAVE_HUGEPAGES
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#error "Systems without huge pages are currently unsupported because i'm a dumb bitch"
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#endif
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#if DMAP_OFFSET % HUGEPAGE_SIZE != 0
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#error "DMAP_OFFSET must be an integral multiple of HUGEPAGE_SIZE"
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#endif
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/* this should be impossible because arch/page.h must also define PAGE_SHIFT
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* and HUGEPAGE_SHIFT, meaning the two are definitively powers of 2 */
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#if HUGEPAGE_SIZE % PAGE_SIZE != 0
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#error "HUGEPAGE_SIZE must be an integral multiple of PAGE_SIZE"
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#endif
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#if PAGE_SIZE % LONG_BIT != 0
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#error "PAGE_SIZE must be an integral multiple of LONG_BIT"
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#endif
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#if CFG_DEBUG_PAGE_ALLOCS
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#define page_debug(msg, ...) kprintf("[page] " msg, ##__VA_ARGS__)
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#else
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#define page_debug(msg, ...)
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#endif
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/**
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* We have cache levels for areas ranging from a single page up to a huge page
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* on a logarithmic scale. Every level covers double the pages per entry than
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* the one below it, starting at one page per entry. The effective result is
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* that a single entry in the cache on level L covers `(1 << L)` pages.
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*/
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#define CACHE_LEVELS (HUGEPAGE_SHIFT - PAGE_SHIFT + 1)
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/** @brief There is one of this for every cache level. */
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struct cache_pool {
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/**
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* @brief List of free blocks on this level of granularity.
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* The individual entries sit right at the beginning of each free block,
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* and are always aligned to `entry_size` bytes.
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*/
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struct clist freelist;
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/**
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* @brief Bitmap that stores the allocated status of each entry.
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* 1 means allocated, 0 means not.
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*/
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unsigned long *bitmap;
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/** @brief Number of items in `freelist`. */
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usize free_entries;
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};
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static struct cache_pool caches[CACHE_LEVELS];
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MTX(caches_lock);
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#define LONG_BIT_MASK (~(LONG_BIT - 1))
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uintptr_t phys_start;
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uintptr_t phys_end;
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static int sanity_check(void)
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{
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if (phys_end != HUGEPAGE_ALIGN(phys_end) || phys_start != HUGEPAGE_ALIGN(phys_start)) {
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kprintf("Unaligned memory, this should never be possible\n");
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return 1;
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}
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if ((phys_end - phys_start) < (32 * 1024 * 1024)) {
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kprintf("Less than 32 MB of usable RAM, this wouldn't go well\n");
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return 1;
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}
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if (phys_start > phys_end) {
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kprintf("Hey, this is funny. pages_init() was called with parameters "
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"such that phys_start > phys_end (%p > %p), which "
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"should absolutely never be possible. I can't really continue "
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"like this, so have a nice day.\n", (void *)phys_start, (void *)phys_end);
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return 1;
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}
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return 0;
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}
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/*
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* This function maps the entire physical memory into the direct region
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* (DMAP_START - DMAP_END) and sets up the caches.
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* The bitmaps are stored one after another at the end of physical memory, and
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*
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*/
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int pages_init(void)
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{
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usize phys_size = phys_end - phys_start;
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if (sanity_check() != 0)
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return 1;
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/*
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* map entire physical memory into the direct contiguous area
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*/
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for (uintptr_t physptr = phys_start; physptr < phys_end; physptr += HUGEPAGE_SIZE) {
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const enum mm_page_flags pflags = MM_PAGE_HUGE | MM_PAGE_RW | MM_PAGE_GLOBAL;
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map_page(physptr, (void *)(physptr + DMAP_OFFSET), pflags);
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}
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vm_flush();
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/*
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* calculate the size of each bitmap, as well as their combined size
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*/
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usize bitmap_bytes = 0;
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for (int i = 0; i < CACHE_LEVELS; i++) {
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usize bits = phys_size >> (PAGE_SHIFT + i);
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/* round up to the next full long */
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if (bits & ~LONG_BIT_MASK) {
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bits &= LONG_BIT_MASK;
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bits += LONG_BIT;
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}
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bitmap_bytes += bits / 8;
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}
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page_debug("Page frame overhead = %zu bytes\n", bitmap_bytes);
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/*
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* zero out all bitmaps
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*/
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uintptr_t bitmap_start_phys = phys_end - bitmap_bytes;
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unsigned long *bitmap_start = __v(bitmap_start_phys);
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memset(bitmap_start, 0, bitmap_bytes);
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/*
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* populate the remaining members of the cache_pool structures and
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* preallocate entries that can't be handed out (i.e. the cache bitmaps)
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*/
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unsigned long *bitmap_pos = bitmap_start;
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for (int i = 0; i < CACHE_LEVELS; i++) {
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/* total amount of entries on this level */
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usize total_bits = phys_size >> (PAGE_SHIFT + i);
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/* number of entries on this level that the bitmap itself takes up */
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usize wasted_bits = bitmap_bytes >> (PAGE_SHIFT + i);
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if (wasted_bits == 0)
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wasted_bits = 1;
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bit_set_range(bitmap_pos, total_bits - wasted_bits, wasted_bits);
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caches[i].bitmap = bitmap_pos;
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bitmap_pos += total_bits / LONG_BIT;
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clist_init(&caches[i].freelist);
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caches[i].free_entries = 0;
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}
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/* kheap_start and kheap_end are globals */
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kheap_start = __v(phys_start);
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kheap_end = ptr_align(bitmap_start, -HUGEPAGE_SHIFT);
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/*
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* populate the freelist on the highest level, all levels beneath it
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* stay empty until one of the large blocks gets split up
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*/
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struct cache_pool *high_pool = &caches[CACHE_LEVELS - 1];
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usize step = 1 << (PAGE_SHIFT + CACHE_LEVELS - 1);
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for (void *pos = kheap_start; pos < kheap_end; pos += step) {
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struct clist *entry = pos;
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clist_add(&high_pool->freelist, entry);
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high_pool->free_entries++;
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}
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return 0;
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}
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/**
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* @brief Split a block and return the lower half.
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* The block is assumed to already have been removed from its freelist.
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* The high half (i.e. the block that is *not* returned) is inserted into the
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* freelist one level below `level`.
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*
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* @param ptr Pointer to the block
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* @param level Current level of the block
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* (`ptr` must be aligned to `1 << level` pages)
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*/
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static void *split_buddy(void *ptr, int level);
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/**
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* @brief Attempt to coalesce a block with its buddy.
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* If coalition is possible, the buddy is removed from its freelist at
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* `level` and the union block is inserted at `level + 1`.
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*
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* @param ptr Pointer to the block
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* @param level Cache level, must be less than `CACHE_LEVELS - 1` (because you
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* can't join blocks at the highest cache level)
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* @return The joined block, or `nil` if coalition was not possible
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*/
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static void *try_join_buddy(void *ptr, int level);
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static usize get_bit_number(void *ptr, int level);
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static int get_level(usize count)
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{
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int level;
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for (level = 0; level < CACHE_LEVELS; level++) {
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if ((1 << level) >= count)
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break;
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}
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return level;
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}
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void *get_pages(usize count, enum mm_flags flags)
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{
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int level = get_level(count);
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if (level == CACHE_LEVELS) {
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page_debug("get_pages(%zu, %08x): count too large!\n", count, flags);
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return nil;
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}
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if (flags & MM_NOSLEEP) {
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kprintf("get_pages(): MM_NOSLEEP requested, this is not implemented yet :(\n");
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return nil;
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}
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mtx_lock(&caches_lock);
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struct clist *entry;
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int entry_level;
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for (entry_level = level; entry_level < CACHE_LEVELS; entry_level++) {
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if (caches[entry_level].free_entries > 0) {
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entry = caches[entry_level].freelist.next;
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break;
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}
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}
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if (entry_level == CACHE_LEVELS) {
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mtx_unlock(&caches_lock);
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return nil;
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}
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clist_del(entry);
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caches[entry_level].free_entries--;
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usize bit_number = get_bit_number(entry, entry_level);
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while (entry_level > level) {
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entry = split_buddy(entry, entry_level);
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bit_set(caches[entry_level].bitmap, bit_number);
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entry_level--;
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bit_number <<= 1;
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}
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bit_set(caches[level].bitmap, bit_number);
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mtx_unlock(&caches_lock);
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return (void *)entry;
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}
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void free_pages(void *ptr, usize count)
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{
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int level = get_level(count);
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if (level == CACHE_LEVELS) {
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page_debug("free_pages(%p, %zu): count too large!\n", ptr, count);
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return;
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}
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mtx_lock(&caches_lock);
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usize bit_number = get_bit_number(ptr, level);
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# if CFG_DEBUG_PAGE_ALLOCS
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if (!bit_tst(caches[level].bitmap, bit_number)) {
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kprintf("free_pages(%p, %zu): double free!\n", ptr, count);
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mtx_unlock(&caches_lock);
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return;
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}
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# endif
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bit_clr(caches[level].bitmap, bit_number);
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while (level < CACHE_LEVELS - 1) {
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bit_clr(ptr, bit_number);
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ptr = try_join_buddy(ptr, level);
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if (ptr == nil)
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break;
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level++;
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bit_number >>= 1;
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}
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mtx_unlock(&caches_lock);
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}
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static inline usize get_bit_number(void *ptr, int level)
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{
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return ((uintptr_t)ptr - (uintptr_t)kheap_start) >> (PAGE_SHIFT + level);
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}
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static inline void *split_buddy(void *ptr, int level)
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{
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# if CFG_DEBUG_PAGE_ALLOCS
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if ((uintptr_t)ptr % (1 << (PAGE_SHIFT + level))) {
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kprintf("split_buddy(ptr = %p, level = %d): unaligned ptr!\n", ptr, level);
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return nil;
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}
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if (level < 1 || level >= CACHE_LEVELS) {
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kprintf("split_buddy(ptr = %p, level = %d): invalid level!\n", ptr, level);
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return nil;
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}
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# endif
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struct clist *high_buddy = ptr + (1 << (PAGE_SHIFT + level - 1));
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clist_add(&caches[level - 1].freelist, high_buddy);
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caches[level - 1].free_entries++;
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page_debug("split (%p:%p), lvl=%d\n", ptr, (void *)high_buddy, level);
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return ptr;
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}
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static void *try_join_buddy(void *ptr, int level)
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{
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const usize entry_size = 1 << (PAGE_SHIFT + level);
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# if CFG_DEBUG_PAGE_ALLOCS
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if ((uintptr_t)ptr % entry_size) {
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kprintf("try_join_buddy(%p, %d): unaligned ptr!\n", ptr, level);
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return nil;
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}
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/* level must be < CACHE_LEVELS - 1 because you
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* can't join blocks on the topmost level */
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if (level >= CACHE_LEVELS - 1) {
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kprintf("try_join_buddy(%p, %d): level >= CACHE_LEVELS - 1!\n", ptr, level);
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return nil;
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}
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# endif
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/*
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* Test whether the buddy block is allocated and return nil if it is.
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* entry_size is a power of 2, so we can quickly get to the buddy block
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* with a cheap XOR of the address and the entry size without the need
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* for any if branches.
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*/
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uintptr_t buddy = (uintptr_t)ptr ^ entry_size;
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usize buddy_bitnum = get_bit_number((void *)buddy, level);
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if (bit_tst(caches[level].bitmap, buddy_bitnum))
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return nil;
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page_debug("join (%p:%p), lvl=%d\n", ptr, (void *)buddy, level);
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/* If the buddy is free, we remove it from the freelist ... */
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clist_del((struct clist *)buddy);
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caches[level].free_entries--;
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/*
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* ... and add the coalesced block to the freelist one level above.
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* We use the same trick as above to get to the even (lower) block, just
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* that this time we're zeroing the bit out rather than flipping it.
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*/
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uintptr_t even = (uintptr_t)ptr & ~entry_size;
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clist_add(&caches[level + 1].freelist, (struct clist *)even);
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caches[level + 1].free_entries++;
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return (void *)even;
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}
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
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* (CNPL) as found in the LICENSE file in the source code root directory
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* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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* of the license, or (at your option) any later version.
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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