On 8/14/20 5:10 PM, Claudio Imbrenda wrote:
> This is a complete rewrite of the page allocator.
>
> This will bring a few improvements:
> * no need to specify the size when freeing
> * allocate small areas with a large alignment without wasting memory
> * ability to initialize and use multiple memory areas (e.g. DMA)
> * more sanity checks
>
> A few things have changed:
> * initialization cannot be done with free_pages like before,
> page_alloc_init_area has to be used instead
>
> Arch-specific changes:
> * arm and x86 have been adapted to put all the memory in just one big
> area (or two, for x86_64 with highmem).
> * s390x instead creates one area below 2GiB and one above; the area
> below 2GiB is used for SMP lowcore initialization.
>
> Details:
> Each memory area has metadata at the very beginning. The metadata is a
> byte array with one entry per usable page (so, excluding the metadata
> itself). Each entry indicates if the page is special (unused for now),
> if it is allocated, and the order of the block. Both free and allocated
> pages are part of larger blocks.
>
> Some more fixed size metadata is present in a fixed-size static array.
> This metadata contains start and end page frame numbers, the pointer to
> the metadata array, and the array of freelists. The array of freelists
> has an entry for each possible order (indicated by the macro NLISTS,
> defined as BITS_PER_LONG - PAGE_SHIFT).
>
> On allocation, if the free list for the needed size is empty, larger
> blocks are split. When a small allocation with a large alignment is
> requested, an appropriately large block is split, to guarantee the
> alignment.
>
> When a block is freed, an attempt will be made to merge it into the
> neighbour, iterating the process as long as possible.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
I'm not sure if it's possible without too much work, but splitting this
would make my brain hurt less upon reading. I'll try continuing review
tomorrow being wide awake for review is preferable for this patch.
Some comments below:
> ---
> lib/alloc_page.h | 64 ++++++-
> lib/alloc_page.c | 451 ++++++++++++++++++++++++++++++++++++-----------
> lib/arm/setup.c | 2 +-
> lib/s390x/sclp.c | 11 +-
> lib/s390x/smp.c | 2 +-
> lib/vmalloc.c | 13 +-
> 6 files changed, 427 insertions(+), 116 deletions(-)
>
> diff --git a/lib/alloc_page.h b/lib/alloc_page.h
> index 88540d1..6472abd 100644
> --- a/lib/alloc_page.h
> +++ b/lib/alloc_page.h
[..]
> diff --git a/lib/alloc_page.c b/lib/alloc_page.c
> index 74fe726..7c91f91 100644
> --- a/lib/alloc_page.c
> +++ b/lib/alloc_page.c
> @@ -13,165 +13,410 @@
> #include <asm/io.h>
> #include <asm/spinlock.h>
>
> +#define IS_ALIGNED_ORDER(x,order) IS_ALIGNED((x),BIT_ULL(order))
> +#define NLISTS ((BITS_PER_LONG) - (PAGE_SHIFT))
> +#define PFN(x) ((uintptr_t)(x) >> PAGE_SHIFT)
So, more or less virt_to_pfn but with uintptr_t rather than unsigned long?
> +
> +#define MAX_AREAS 4
> +
> +#define ORDER_MASK 0x3f
> +#define ALLOC_MASK 0x40
> +
> +struct free_list {
> + struct free_list *prev;
> + struct free_list *next;
> +};
> +
> +struct mem_area {
> + /* Physical frame number of the first usable frame in the area */
> + uintptr_t base;
> + /* Physical frame number of the first frame outside the area */
> + uintptr_t top;
> + /* Combination ALLOC_MASK and order */
> + u8 *page_states;
> + /* One freelist for each possible block size, up to NLISTS */
> + struct free_list freelists[NLISTS];
> +};
> +
> +static struct mem_area areas[MAX_AREAS];
> +static unsigned int areas_mask;
> static struct spinlock lock;
> -static void *freelist = 0;
>
> bool page_alloc_initialized(void)
> {
> - return freelist != 0;
> + return areas_mask != 0;
> }
>
> -void free_pages(void *mem, size_t size)
> +static inline bool area_overlaps(struct mem_area *a, uintptr_t pfn)
> {
> - void *old_freelist;
> - void *end;
> + return (pfn >= PFN(a->page_states)) && (pfn < a->top);
> +}
I have pondered over this function for quite a while now and I don't
think the naming is correct.
This is basically the contains function below, but including the page
states which are at the beginning of the area but will never be shown to
users, right?
>
> - assert_msg((unsigned long) mem % PAGE_SIZE == 0,
> - "mem not page aligned: %p", mem);
> +static inline bool area_contains(struct mem_area *a, uintptr_t pfn)
> +{
> + return (pfn >= a->base) && (pfn < a->top);
> +}
>
> - assert_msg(size % PAGE_SIZE == 0, "size not page aligned: %#zx", size);
> +static inline bool is_list_empty(struct free_list *p)
> +{
> + return !p->next || !p->prev || p == p->next || p == p->prev;
> +}
>
> - assert_msg(size == 0 || (uintptr_t)mem == -size ||
> - (uintptr_t)mem + size > (uintptr_t)mem,
> - "mem + size overflow: %p + %#zx", mem, size);
> +static struct free_list *list_remove(struct free_list *l)
> +{
> + if (is_list_empty(l))
> + return NULL;
>
> - if (size == 0) {
> - freelist = NULL;
> - return;
> - }
> + l->prev->next = l->next;
> + l->next->prev = l->prev;
> + l->prev = l->next = NULL;
>
> - spin_lock(&lock);
> - old_freelist = freelist;
> - freelist = mem;
> - end = mem + size;
> - while (mem + PAGE_SIZE != end) {
> - *(void **)mem = (mem + PAGE_SIZE);
> - mem += PAGE_SIZE;
> - }
> + return l;
> +}
>
> - *(void **)mem = old_freelist;
> - spin_unlock(&lock);
> +static void list_add(struct free_list *head, struct free_list *li)
> +{
> + assert(li);
> + assert(head);
> + li->prev = head;
> + li->next = head->next;
> + head->next->prev = li;
> + head->next = li;
> }
lib/lists.(c|h) or maybe util.c
I guess it's only a matter of time until we have a fully preempt testing
kernel...
>
> -void free_pages_by_order(void *mem, unsigned int order)
> +/*
> + * Splits the free block starting at addr into 2 blocks of half the size.
> + *
> + * The function depends on the following assumptions:
> + * - The allocator must have been initialized
> + * - the block must be within the memory area
> + * - all pages in the block must be free and not special
> + * - the pointer must point to the start of the block
> + * - all pages in the block must have the same block size.
> + * - the block size must be greater than 0
> + * - the block size must be smaller than the maximum allowed
> + * - the block must be in a free list
> + * - the function is called with the lock held
> + */
> +static void split(struct mem_area *a, void *addr)
> {
> - free_pages(mem, 1ul << (order + PAGE_SHIFT));
> + uintptr_t pfn = PFN(addr);
> + struct free_list *p;
> + uintptr_t i, idx;
> + u8 order;
> +
> + assert(a && area_contains(a, pfn));
> + idx = pfn - a->base;
> + order = a->page_states[idx];
> + assert(!(order & ~ORDER_MASK) && order && (order < NLISTS));
> + assert(IS_ALIGNED_ORDER(pfn, order));
> + assert(area_contains(a, pfn + BIT(order) - 1));
> +
> + /* Remove the block from its free list */
> + p = list_remove(addr);
> + assert(p);
> +
> + /* update the block size for each page in the block */
> + for (i = 0; i < BIT(order); i++) {
> + assert(a->page_states[idx + i] == order);
> + a->page_states[idx + i] = order - 1;
> + }
> + order--;
> + /* add the first half block to the appropriate free list */
> + list_add(a->freelists + order, p);
> + /* add the second half block to the appropriate free list */
> + list_add(a->freelists + order, (void *)((pfn + BIT(order)) * PAGE_SIZE));
> }
>
> -void *alloc_page()
> +/*
> + * Returns a block whose alignment and size are at least the parameter values.
> + * If there is not enough free memory, NULL is returned.
> + *
> + * Both parameters must be not larger than the largest allowed order
> + */
> +static void *page_memalign_order(struct mem_area *a, u8 al, u8 sz)
> {
> - void *p;
> + struct free_list *p, *res = NULL;
> + u8 order;
>
> - if (!freelist)
> - return 0;
> + assert((al < NLISTS) && (sz < NLISTS));
> + /* we need the bigger of the two as starting point */
> + order = sz > al ? sz : al;
>
> - spin_lock(&lock);
> - p = freelist;
> - freelist = *(void **)freelist;
> - spin_unlock(&lock);
> + /* search all free lists for some memory */
> + for ( ; order < NLISTS; order++) {
> + p = a->freelists[order].next;
> + if (!is_list_empty(p))
> + break;
> + }
> + /* out of memory */
> + if (order >= NLISTS)
> + return NULL;
> +
> + /*
> + * the block is bigger than what we need because either there were
> + * no smaller blocks, or the smaller blocks were not aligned to our
> + * needs; therefore we split the block until we reach the needed size
> + */
> + for (; order > sz; order--)
> + split(a, p);
>
> - if (p)
> - memset(p, 0, PAGE_SIZE);
> - return p;
> + res = list_remove(p);
> + memset(a->page_states + (PFN(res) - a->base), ALLOC_MASK | order, BIT(order));
> + return res;
> }
>
> /*
> - * Allocates (1 << order) physically contiguous and naturally aligned pages.
> - * Returns NULL if there's no memory left.
> + * Try to merge two blocks into a bigger one.
> + * Returns true in case of a successful merge.
> + * Merging will succeed only if both blocks have the same block size and are
> + * both free.
> + *
> + * The function depends on the following assumptions:
> + * - the first parameter is strictly smaller than the second
> + * - the parameters must point each to the start of their block
> + * - the two parameters point to adjacent blocks
> + * - the two blocks are both in a free list
> + * - all of the pages of the two blocks must be free
> + * - all of the pages of the two blocks must have the same block size
> + * - the function is called with the lock held
> */
> -void *alloc_pages(unsigned int order)
> +static bool coalesce(struct mem_area *a, u8 order, uintptr_t pfn, uintptr_t pfn2)
> {
> - /* Generic list traversal. */
> - void *prev;
> - void *curr = NULL;
> - void *next = freelist;
> + uintptr_t first, second, i;
> + struct free_list *li;
>
> - /* Looking for a run of length (1 << order). */
> - unsigned long run = 0;
> - const unsigned long n = 1ul << order;
> - const unsigned long align_mask = (n << PAGE_SHIFT) - 1;
> - void *run_start = NULL;
> - void *run_prev = NULL;
> - unsigned long run_next_pa = 0;
> - unsigned long pa;
> + assert(IS_ALIGNED_ORDER(pfn, order) && IS_ALIGNED_ORDER(pfn2, order));
> + assert(pfn2 == pfn + BIT(order));
> + assert(a);
>
> - assert(order < sizeof(unsigned long) * 8);
> + if (!area_contains(a, pfn) || !area_contains(a, pfn2 + BIT(order) - 1))
> + return false;
> + first = pfn - a->base;
> + second = pfn2 - a->base;
> + if ((a->page_states[first] != order) || (a->page_states[second] != order))
> + return false;
>
> - spin_lock(&lock);
> - for (;;) {
> - prev = curr;
> - curr = next;
> + li = list_remove((void *)(pfn2 << PAGE_SHIFT));
> + assert(li);
> + li = list_remove((void *)(pfn << PAGE_SHIFT));
> + assert(li);
> + for (i = 0; i < (2ull << order); i++) {
> + assert(a->page_states[first + i] == order);
> + a->page_states[first + i] = order + 1;
> + }
> + list_add(a->freelists + order + 1, li);
> + return true;
> +}
>
> - if (!curr) {
> - run_start = NULL;
> - break;
> - }
> +/*
> + * Free a block of memory.
> + * The parameter can be NULL, in which case nothing happens.
> + *
> + * The function depends on the following assumptions:
> + * - the parameter is page aligned
> + * - the parameter belongs to an existing memory area
> + * - the parameter points to the beginning of the block
> + * - the size of the block is less than the maximum allowed
> + * - the block is completely contained in its memory area
> + * - all pages in the block have the same block size
> + * - no pages in the memory block were already free
> + * - no pages in the memory block are special
> + */
> +static void _free_pages(void *mem)
> +{
> + uintptr_t pfn2, pfn = PFN(mem);
> + struct mem_area *a = NULL;
> + uintptr_t i, p;
> + u8 order;
>
> - next = *((void **) curr);
> - pa = virt_to_phys(curr);
> -
> - if (run == 0) {
> - if (!(pa & align_mask)) {
> - run_start = curr;
> - run_prev = prev;
> - run_next_pa = pa + PAGE_SIZE;
> - run = 1;
> - }
> - } else if (pa == run_next_pa) {
> - run_next_pa += PAGE_SIZE;
> - run += 1;
> - } else {
> - run = 0;
> - }
> + if (!mem)
> + return;
> + assert(IS_ALIGNED((uintptr_t)mem, PAGE_SIZE));
> + for (i = 0; !a && (i < MAX_AREAS); i++) {
> + if ((areas_mask & BIT(i)) && area_contains(areas + i, pfn))
> + a = areas + i;
> + }
> + assert_msg(a, "memory does not belong to any area: %p", mem);
>
> - if (run == n) {
> - if (run_prev)
> - *((void **) run_prev) = next;
> - else
> - freelist = next;
> - break;
> - }
> + p = pfn - a->base;
> + order = a->page_states[p] & ORDER_MASK;
> +
> + assert(a->page_states[p] == (order | ALLOC_MASK));
> + assert(order < NLISTS);
> + assert(IS_ALIGNED_ORDER(pfn, order));
> + assert(area_contains(a, pfn + BIT(order) - 1));
> +
> + for (i = 0; i < BIT(order); i++) {
> + assert(a->page_states[p + i] == (ALLOC_MASK | order));
> + a->page_states[p + i] &= ~ALLOC_MASK;
> }
> - spin_unlock(&lock);
> - if (run_start)
> - memset(run_start, 0, n * PAGE_SIZE);
> - return run_start;
> + list_add(a->freelists + order, mem);
> + do {
> + order = a->page_states[p] & ORDER_MASK;
> + if (!IS_ALIGNED_ORDER(pfn, order + 1))
> + pfn = pfn - BIT(order);
> + pfn2 = pfn + BIT(order);
> + } while (coalesce(a, order, pfn, pfn2));
> }
>
> +void free_pages(void *mem, size_t size)
> +{
> + spin_lock(&lock);
> + _free_pages(mem);
> + spin_unlock(&lock);
> +}
>
> -void free_page(void *page)
> +static void *page_memalign_order_area(unsigned area, u8 ord, u8 al)
> {
> + void *res = NULL;
> + int i;
> +
> spin_lock(&lock);
> - *(void **)page = freelist;
> - freelist = page;
> + area &= areas_mask;
> + for (i = 0; !res && (i < MAX_AREAS); i++)
> + if (area & BIT(i))
> + res = page_memalign_order(areas + i, ord, al);
> spin_unlock(&lock);
> + return res;
> }
>
> -static void *page_memalign(size_t alignment, size_t size)
> +/*
> + * Allocates (1 << order) physically contiguous and naturally aligned pages.
> + * Returns NULL if the allocation was not possible.
> + */
> +void *alloc_pages_area(unsigned int area, unsigned int order)
> {
> - unsigned long n = ALIGN(size, PAGE_SIZE) >> PAGE_SHIFT;
> - unsigned int order;
> + return page_memalign_order_area(area, order, order);
> +}
>
> - if (!size)
> - return NULL;
> +void *alloc_pages(unsigned int order)
> +{
> + return alloc_pages_area(~0, order);
> +}
>
> - order = get_order(n);
> +/*
> + * Allocates (1 << order) physically contiguous aligned pages.
> + * Returns NULL if the allocation was not possible.
> + */
> +void *memalign_pages_area(unsigned int area, size_t alignment, size_t size)
> +{
> + assert(is_power_of_2(alignment));
> + alignment = get_order(PAGE_ALIGN(alignment) >> PAGE_SHIFT);
> + size = get_order(PAGE_ALIGN(size) >> PAGE_SHIFT);
> + assert(alignment < NLISTS);
> + assert(size < NLISTS);
> + return page_memalign_order_area(area, size, alignment);
> +}
>
> - return alloc_pages(order);
> +void *memalign_pages(size_t alignment, size_t size)
> +{
> + return memalign_pages_area(~0, alignment, size);
> }
>
> -static void page_free(void *mem, size_t size)
> +/*
> + * Allocates one page
> + */
> +void *alloc_page()
> {
> - free_pages(mem, size);
> + return alloc_pages(0);
> }
>
> static struct alloc_ops page_alloc_ops = {
> - .memalign = page_memalign,
> - .free = page_free,
> + .memalign = memalign_pages,
> + .free = free_pages,
> .align_min = PAGE_SIZE,
> };
>
> +/*
> + * Enables the page allocator.
> + *
> + * Prerequisites:
> + * - at least one memory area has been initialized
> + */
> void page_alloc_ops_enable(void)
> {
> + spin_lock(&lock);
> + assert(page_alloc_initialized());
> alloc_ops = &page_alloc_ops;
> + spin_unlock(&lock);
> +}
> +
> +/*
> + * Adds a new memory area to the pool of available memory.
> + *
> + * Prerequisites:
> + * - the lock is held
> + * - start and top are page frame numbers
Calling them pfn_start and pfn_top would make that clearer.
Maybe add a list of the input parameters and their contents?
> + * - start is smaller than top
> + * - top does not fall outside of addressable memory
> + * - there is at least one more slot free for memory areas
> + * - if a specific memory area number has been indicated, it needs to be free
> + * - the memory area to add does not overlap with existing areas
> + * - the memory area to add has at least 5 pages available
> + */
> +static void _page_alloc_init_area(int n, uintptr_t start, uintptr_t top)
> +{
> + size_t table_size, npages, i;
> + struct mem_area *a;
> + u8 order = 0;
> +
> + if (n == -1) {
> + for (n = 0; n < MAX_AREAS; n++) {
> + if (!(areas_mask & BIT(n)))
> + break;
> + }
> + }
> + assert(n < MAX_AREAS);
> + assert(!(areas_mask & BIT(n)));
> +
> + assert(top > start);
> + assert(top - start > 4);
> + assert(top < BIT_ULL(sizeof(void *) * 8 - PAGE_SHIFT));
> +
> + table_size = (top - start + PAGE_SIZE) / (PAGE_SIZE + 1);
> +
> + a = areas + n;
> + a->page_states = (void *)(start << PAGE_SHIFT);
> + a->base = start + table_size;
> + a->top = top;
> + npages = top - a->base;
> +
> + assert((a->base - start) * PAGE_SIZE >= npages);
> + for (i = 0; i < MAX_AREAS; i++) {
> + if (!(areas_mask & BIT(i)))
> + continue;
> + assert(!area_overlaps(areas + i, start));
> + assert(!area_overlaps(areas + i, top - 1));
> + assert(!area_overlaps(a, PFN(areas[i].page_states)));
> + assert(!area_overlaps(a, areas[i].top - 1));
> + }
> + for (i = 0; i < NLISTS; i++)
> + a->freelists[i].next = a->freelists[i].prev = a->freelists + i;
> +
> + for (i = a->base; i < a->top; i += 1ull << order) {
> + while (i + BIT(order) > a->top) {
> + assert(order);
> + order--;
> + }
> + while (IS_ALIGNED_ORDER(i, order + 1) && (i + BIT(order + 1) <= a->top))
> + order++;
> + assert(order < NLISTS);
> + memset(a->page_states + (i - a->base), order, BIT(order));
> + list_add(a->freelists + order, (void *)(i << PAGE_SHIFT));
> + }
> + areas_mask |= BIT(n);
> +}
> +
> +/*
> + * Adds a new memory area to the pool of available memory.
> + *
> + * Prerequisites:
> + * see _page_alloc_init_area
> + */
> +void page_alloc_init_area(int n, uintptr_t base_pfn, uintptr_t top_pfn)
> +{
> + spin_lock(&lock);
> + _page_alloc_init_area(n, base_pfn, top_pfn);
> + spin_unlock(&lock);
> }
> diff --git a/lib/arm/setup.c b/lib/arm/setup.c
> index 78562e4..a3c573f 100644
> --- a/lib/arm/setup.c
> +++ b/lib/arm/setup.c
> @@ -155,7 +155,7 @@ static void mem_init(phys_addr_t freemem_start)
> assert(sizeof(long) == 8 || !(base >> 32));
> if (sizeof(long) != 8 && (top >> 32) != 0)
> top = ((uint64_t)1 << 32);
> - free_pages((void *)(unsigned long)base, top - base);
> + page_alloc_init_area(-1, base, top);
> page_alloc_ops_enable();
> }
>
> diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
> index 4054d0e..c25d442 100644
> --- a/lib/s390x/sclp.c
> +++ b/lib/s390x/sclp.c
> @@ -37,11 +37,16 @@ static void mem_init(phys_addr_t mem_end)
>
> phys_alloc_init(freemem_start, mem_end - freemem_start);
> phys_alloc_get_unused(&base, &top);
> - base = (base + PAGE_SIZE - 1) & -PAGE_SIZE;
> - top = top & -PAGE_SIZE;
> + base = PAGE_ALIGN(base) >> PAGE_SHIFT;
> + top = top >> PAGE_SHIFT;
>
> /* Make the pages available to the physical allocator */
> - free_pages((void *)(unsigned long)base, top - base);
> + if (top > (2ull * SZ_1G >> PAGE_SHIFT)) {
> + page_alloc_init_area(0, 2ull * SZ_1G >> PAGE_SHIFT, top);
> + page_alloc_init_area(1, base, 2ull * SZ_1G >> PAGE_SHIFT);
> + } else {
> + page_alloc_init_area(1, base, top);
> + }
> page_alloc_ops_enable();
> }
>
> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
> index 2860e9c..d954094 100644
> --- a/lib/s390x/smp.c
> +++ b/lib/s390x/smp.c
> @@ -190,7 +190,7 @@ int smp_cpu_setup(uint16_t addr, struct psw psw)
>
> sigp_retry(cpu->addr, SIGP_INITIAL_CPU_RESET, 0, NULL);
>
> - lc = alloc_pages(1);
> + lc = alloc_pages_area(_AREA(1), 1);
> cpu->lowcore = lc;
> memset(lc, 0, PAGE_SIZE * 2);
> sigp_retry(cpu->addr, SIGP_SET_PREFIX, (unsigned long )lc, NULL);
> diff --git a/lib/vmalloc.c b/lib/vmalloc.c
> index aca0876..f72c5b3 100644
> --- a/lib/vmalloc.c
> +++ b/lib/vmalloc.c
> @@ -217,18 +217,19 @@ void setup_vm()
> * so that it can be used to allocate page tables.
> */
> if (!page_alloc_initialized()) {
> - base = PAGE_ALIGN(base);
> - top = top & -PAGE_SIZE;
> - free_pages(phys_to_virt(base), top - base);
> + base = PAGE_ALIGN(base) >> PAGE_SHIFT;
> + top = top >> PAGE_SHIFT;
> + page_alloc_init_area(1, base, top);
> + page_alloc_ops_enable();
> }
>
> find_highmem();
> phys_alloc_get_unused(&base, &top);
> page_root = setup_mmu(top);
> if (base != top) {
> - base = PAGE_ALIGN(base);
> - top = top & -PAGE_SIZE;
> - free_pages(phys_to_virt(base), top - base);
> + base = PAGE_ALIGN(base) >> PAGE_SHIFT;
> + top = top >> PAGE_SHIFT;
> + page_alloc_init_area(0, base, top);
> }
>
> spin_lock(&lock);
>
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