staging: zsmalloc: zsmalloc memory allocation library (61989a80) · Commits · e / devices / android_kernel_samsung_universal8895

drivers/staging/zsmalloc/Kconfig

0 → 100644

+11 −0

Original line number	Diff line number	Diff line
		config ZSMALLOC
		tristate "Memory allocator for compressed pages"
		depends on SPARSEMEM
		default n
		help
		zsmalloc is a slab-based memory allocator designed to store
		compressed RAM pages. zsmalloc uses virtual memory mapping
		in order to reduce fragmentation. However, this results in a
		non-standard allocator interface where a handle, not a pointer, is
		returned by an alloc(). This handle must be mapped in order to
		access the allocated space.

drivers/staging/zsmalloc/Makefile

0 → 100644

+3 −0

Original line number	Diff line number	Diff line
		zsmalloc-y := zsmalloc-main.o

		obj-$(CONFIG_ZSMALLOC) += zsmalloc.o

drivers/staging/zsmalloc/zsmalloc-main.c

0 → 100644

+756 −0

Original line number	Diff line number	Diff line
		/*
		* zsmalloc memory allocator
		*
		* Copyright (C) 2011 Nitin Gupta
		*
		* This code is released using a dual license strategy: BSD/GPL
		* You can choose the license that better fits your requirements.
		*
		* Released under the terms of 3-clause BSD License
		* Released under the terms of GNU General Public License Version 2.0
		*/

		#ifdef CONFIG_ZSMALLOC_DEBUG
		#define DEBUG
		#endif

		#include <linux/module.h>
		#include <linux/kernel.h>
		#include <linux/bitops.h>
		#include <linux/errno.h>
		#include <linux/highmem.h>
		#include <linux/init.h>
		#include <linux/string.h>
		#include <linux/slab.h>
		#include <asm/tlbflush.h>
		#include <asm/pgtable.h>
		#include <linux/cpumask.h>
		#include <linux/cpu.h>

		#include "zsmalloc.h"
		#include "zsmalloc_int.h"

		/*
		* A zspage's class index and fullness group
		* are encoded in its (first)page->mapping
		*/
		#define CLASS_IDX_BITS 28
		#define FULLNESS_BITS 4
		#define CLASS_IDX_MASK ((1 << CLASS_IDX_BITS) - 1)
		#define FULLNESS_MASK ((1 << FULLNESS_BITS) - 1)

		/*
		* Object location (<PFN>, <obj_idx>) is encoded as
		* as single (void *) handle value.
		*
		* Note that object index <obj_idx> is relative to system
		* page <PFN> it is stored in, so for each sub-page belonging
		* to a zspage, obj_idx starts with 0.
		*/
		#define _PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT)
		#define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS)
		#define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)

		/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
		static DEFINE_PER_CPU(struct mapping_area, zs_map_area);

		static int is_first_page(struct page *page)
		{
		return test_bit(PG_private, &page->flags);
		}

		static int is_last_page(struct page *page)
		{
		return test_bit(PG_private_2, &page->flags);
		}

		static void get_zspage_mapping(struct page page, unsigned int class_idx,
		enum fullness_group *fullness)
		{
		unsigned long m;
		BUG_ON(!is_first_page(page));

		m = (unsigned long)page->mapping;
		*fullness = m & FULLNESS_MASK;
		*class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
		}

		static void set_zspage_mapping(struct page *page, unsigned int class_idx,
		enum fullness_group fullness)
		{
		unsigned long m;
		BUG_ON(!is_first_page(page));

		m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) \|
		(fullness & FULLNESS_MASK);
		page->mapping = (struct address_space *)m;
		}

		static int get_size_class_index(int size)
		{
		int idx = 0;

		if (likely(size > ZS_MIN_ALLOC_SIZE))
		idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
		ZS_SIZE_CLASS_DELTA);

		return idx;
		}

		static enum fullness_group get_fullness_group(struct page *page)
		{
		int inuse, max_objects;
		enum fullness_group fg;
		BUG_ON(!is_first_page(page));

		inuse = page->inuse;
		max_objects = page->objects;

		if (inuse == 0)
		fg = ZS_EMPTY;
		else if (inuse == max_objects)
		fg = ZS_FULL;
		else if (inuse <= max_objects / fullness_threshold_frac)
		fg = ZS_ALMOST_EMPTY;
		else
		fg = ZS_ALMOST_FULL;

		return fg;
		}

		static void insert_zspage(struct page page, struct size_class class,
		enum fullness_group fullness)
		{
		struct page **head;

		BUG_ON(!is_first_page(page));

		if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

		head = &class->fullness_list[fullness];
		if (*head)
		list_add_tail(&page->lru, &(*head)->lru);

		*head = page;
		}

		static void remove_zspage(struct page page, struct size_class class,
		enum fullness_group fullness)
		{
		struct page **head;

		BUG_ON(!is_first_page(page));

		if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

		head = &class->fullness_list[fullness];
		BUG_ON(!*head);
		if (list_empty(&(*head)->lru))
		*head = NULL;
		else if (*head == page)
		head = (struct page )list_entry((*head)->lru.next,
		struct page, lru);

		list_del_init(&page->lru);
		}

		static enum fullness_group fix_fullness_group(struct zs_pool *pool,
		struct page *page)
		{
		int class_idx;
		struct size_class *class;
		enum fullness_group currfg, newfg;

		BUG_ON(!is_first_page(page));

		get_zspage_mapping(page, &class_idx, &currfg);
		newfg = get_fullness_group(page);
		if (newfg == currfg)
		goto out;

		class = &pool->size_class[class_idx];
		remove_zspage(page, class, currfg);
		insert_zspage(page, class, newfg);
		set_zspage_mapping(page, class_idx, newfg);

		out:
		return newfg;
		}

		/*
		* We have to decide on how many pages to link together
		* to form a zspage for each size class. This is important
		* to reduce wastage due to unusable space left at end of
		* each zspage which is given as:
		* wastage = Zp - Zp % size_class
		* where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
		*
		* For example, for size class of 3/8 * PAGE_SIZE, we should
		* link together 3 PAGE_SIZE sized pages to form a zspage
		* since then we can perfectly fit in 8 such objects.
		*/
		static int get_zspage_order(int class_size)
		{
		int i, max_usedpc = 0;
		/* zspage order which gives maximum used size per KB */
		int max_usedpc_order = 1;

		for (i = 1; i <= max_zspage_order; i++) {
		int zspage_size;
		int waste, usedpc;

		zspage_size = i * PAGE_SIZE;
		waste = zspage_size % class_size;
		usedpc = (zspage_size - waste) * 100 / zspage_size;

		if (usedpc > max_usedpc) {
		max_usedpc = usedpc;
		max_usedpc_order = i;
		}
		}

		return max_usedpc_order;
		}

		/*
		* A single 'zspage' is composed of many system pages which are
		* linked together using fields in struct page. This function finds
		* the first/head page, given any component page of a zspage.
		*/
		static struct page get_first_page(struct page page)
		{
		if (is_first_page(page))
		return page;
		else
		return page->first_page;
		}

		static struct page get_next_page(struct page page)
		{
		struct page *next;

		if (is_last_page(page))
		next = NULL;
		else if (is_first_page(page))
		next = (struct page *)page->private;
		else
		next = list_entry(page->lru.next, struct page, lru);

		return next;
		}

		/* Encode <page, obj_idx> as a single handle value */
		static void obj_location_to_handle(struct page page, unsigned long obj_idx)
		{
		unsigned long handle;

		if (!page) {
		BUG_ON(obj_idx);
		return NULL;
		}

		handle = page_to_pfn(page) << OBJ_INDEX_BITS;
		handle \|= (obj_idx & OBJ_INDEX_MASK);

		return (void *)handle;
		}

		/* Decode <page, obj_idx> pair from the given object handle */
		static void obj_handle_to_location(void handle, struct page *page,
		unsigned long *obj_idx)
		{
		unsigned long hval = (unsigned long)handle;

		*page = pfn_to_page(hval >> OBJ_INDEX_BITS);
		*obj_idx = hval & OBJ_INDEX_MASK;
		}

		static unsigned long obj_idx_to_offset(struct page *page,
		unsigned long obj_idx, int class_size)
		{
		unsigned long off = 0;

		if (!is_first_page(page))
		off = page->index;

		return off + obj_idx * class_size;
		}

		static void free_zspage(struct page *first_page)
		{
		struct page nextp, tmp;

		BUG_ON(!is_first_page(first_page));
		BUG_ON(first_page->inuse);

		nextp = (struct page *)page_private(first_page);

		clear_bit(PG_private, &first_page->flags);
		clear_bit(PG_private_2, &first_page->flags);
		set_page_private(first_page, 0);
		first_page->mapping = NULL;
		first_page->freelist = NULL;
		reset_page_mapcount(first_page);
		__free_page(first_page);

		/* zspage with only 1 system page */
		if (!nextp)
		return;

		list_for_each_entry_safe(nextp, tmp, &nextp->lru, lru) {
		list_del(&nextp->lru);
		clear_bit(PG_private_2, &nextp->flags);
		nextp->index = 0;
		__free_page(nextp);
		}
		}

		/* Initialize a newly allocated zspage */
		static void init_zspage(struct page first_page, struct size_class class)
		{
		unsigned long off = 0;
		struct page *page = first_page;

		BUG_ON(!is_first_page(first_page));
		while (page) {
		struct page *next_page;
		struct link_free *link;
		unsigned int i, objs_on_page;

		/*
		* page->index stores offset of first object starting
		* in the page. For the first page, this is always 0,
		* so we use first_page->index (aka ->freelist) to store
		* head of corresponding zspage's freelist.
		*/
		if (page != first_page)
		page->index = off;

		link = (struct link_free *)kmap_atomic(page) +
		off / sizeof(*link);
		objs_on_page = (PAGE_SIZE - off) / class->size;

		for (i = 1; i <= objs_on_page; i++) {
		off += class->size;
		if (off < PAGE_SIZE) {
		link->next = obj_location_to_handle(page, i);
		link += class->size / sizeof(*link);
		}
		}

		/*
		* We now come to the last (full or partial) object on this
		* page, which must point to the first object on the next
		* page (if present)
		*/
		next_page = get_next_page(page);
		link->next = obj_location_to_handle(next_page, 0);
		kunmap_atomic(link);
		page = next_page;
		off = (off + class->size) % PAGE_SIZE;
		}
		}

		/*
		* Allocate a zspage for the given size class
		*/
		static struct page alloc_zspage(struct size_class class, gfp_t flags)
		{
		int i, error;
		struct page *first_page = NULL;

		/*
		* Allocate individual pages and link them together as:
		* 1. first page->private = first sub-page
		* 2. all sub-pages are linked together using page->lru
		* 3. each sub-page is linked to the first page using page->first_page
		*
		* For each size class, First/Head pages are linked together using
		* page->lru. Also, we set PG_private to identify the first page
		* (i.e. no other sub-page has this flag set) and PG_private_2 to
		* identify the last page.
		*/
		error = -ENOMEM;
		for (i = 0; i < class->zspage_order; i++) {
		struct page page, prev_page;

		page = alloc_page(flags);
		if (!page)
		goto cleanup;

		INIT_LIST_HEAD(&page->lru);
		if (i == 0) { /* first page */
		set_bit(PG_private, &page->flags);
		set_page_private(page, 0);
		first_page = page;
		first_page->inuse = 0;
		}
		if (i == 1)
		first_page->private = (unsigned long)page;
		if (i >= 1)
		page->first_page = first_page;
		if (i >= 2)
		list_add(&page->lru, &prev_page->lru);
		if (i == class->zspage_order - 1) /* last page */
		set_bit(PG_private_2, &page->flags);

		prev_page = page;
		}

		init_zspage(first_page, class);

		first_page->freelist = obj_location_to_handle(first_page, 0);
		/* Maximum number of objects we can store in this zspage */
		first_page->objects = class->zspage_order * PAGE_SIZE / class->size;

		error = 0; /* Success */

		cleanup:
		if (unlikely(error) && first_page) {
		free_zspage(first_page);
		first_page = NULL;
		}

		return first_page;
		}

		static struct page find_get_zspage(struct size_class class)
		{
		int i;
		struct page *page;

		for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
		page = class->fullness_list[i];
		if (page)
		break;
		}

		return page;
		}


		/*
		* If this becomes a separate module, register zs_init() with
		* module_init(), zs_exit with module_exit(), and remove zs_initialized
		*/
		static int zs_initialized;

		static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
		void *pcpu)
		{
		int cpu = (long)pcpu;
		struct mapping_area *area;

		switch (action) {
		case CPU_UP_PREPARE:
		area = &per_cpu(zs_map_area, cpu);
		if (area->vm)
		break;
		area->vm = alloc_vm_area(2 * PAGE_SIZE, area->vm_ptes);
		if (!area->vm)
		return notifier_from_errno(-ENOMEM);
		break;
		case CPU_DEAD:
		case CPU_UP_CANCELED:
		area = &per_cpu(zs_map_area, cpu);
		if (area->vm)
		free_vm_area(area->vm);
		area->vm = NULL;
		break;
		}

		return NOTIFY_OK;
		}

		static struct notifier_block zs_cpu_nb = {
		.notifier_call = zs_cpu_notifier
		};

		static void zs_exit(void)
		{
		int cpu;

		for_each_online_cpu(cpu)
		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
		unregister_cpu_notifier(&zs_cpu_nb);
		}

		static int zs_init(void)
		{
		int cpu, ret;

		register_cpu_notifier(&zs_cpu_nb);
		for_each_online_cpu(cpu) {
		ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
		if (notifier_to_errno(ret))
		goto fail;
		}
		return 0;
		fail:
		zs_exit();
		return notifier_to_errno(ret);
		}

		struct zs_pool zs_create_pool(const char name, gfp_t flags)
		{
		int i, error, ovhd_size;
		struct zs_pool *pool;

		if (!name)
		return NULL;

		ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
		pool = kzalloc(ovhd_size, GFP_KERNEL);
		if (!pool)
		return NULL;

		for (i = 0; i < ZS_SIZE_CLASSES; i++) {
		int size;
		struct size_class *class;

		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
		if (size > ZS_MAX_ALLOC_SIZE)
		size = ZS_MAX_ALLOC_SIZE;

		class = &pool->size_class[i];
		class->size = size;
		class->index = i;
		spin_lock_init(&class->lock);
		class->zspage_order = get_zspage_order(size);

		}

		/*
		* If this becomes a separate module, register zs_init with
		* module_init, and remove this block
		*/
		if (!zs_initialized) {
		error = zs_init();
		if (error)
		goto cleanup;
		zs_initialized = 1;
		}

		pool->flags = flags;
		pool->name = name;

		error = 0; /* Success */

		cleanup:
		if (error) {
		zs_destroy_pool(pool);
		pool = NULL;
		}

		return pool;
		}
		EXPORT_SYMBOL_GPL(zs_create_pool);

		void zs_destroy_pool(struct zs_pool *pool)
		{
		int i;

		for (i = 0; i < ZS_SIZE_CLASSES; i++) {
		int fg;
		struct size_class *class = &pool->size_class[i];

		for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
		if (class->fullness_list[fg]) {
		pr_info("Freeing non-empty class with size "
		"%db, fullness group %d\n",
		class->size, fg);
		}
		}
		}
		kfree(pool);
		}
		EXPORT_SYMBOL_GPL(zs_destroy_pool);

		/**
		* zs_malloc - Allocate block of given size from pool.
		* @pool: pool to allocate from
		* @size: size of block to allocate
		* @page: page no. that holds the object
		* @offset: location of object within page
		*
		* On success, <page, offset> identifies block allocated
		* and 0 is returned. On failure, <page, offset> is set to
		* 0 and -ENOMEM is returned.
		*
		* Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
		*/
		void zs_malloc(struct zs_pool pool, size_t size)
		{
		void *obj;
		struct link_free *link;
		int class_idx;
		struct size_class *class;

		struct page first_page, m_page;
		unsigned long m_objidx, m_offset;

		if (unlikely(!size \|\| size > ZS_MAX_ALLOC_SIZE))
		return NULL;

		class_idx = get_size_class_index(size);
		class = &pool->size_class[class_idx];
		BUG_ON(class_idx != class->index);

		spin_lock(&class->lock);
		first_page = find_get_zspage(class);

		if (!first_page) {
		spin_unlock(&class->lock);
		first_page = alloc_zspage(class, pool->flags);
		if (unlikely(!first_page))
		return NULL;

		set_zspage_mapping(first_page, class->index, ZS_EMPTY);
		spin_lock(&class->lock);
		class->pages_allocated += class->zspage_order;
		}

		obj = first_page->freelist;
		obj_handle_to_location(obj, &m_page, &m_objidx);
		m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);

		link = (struct link_free *)kmap_atomic(m_page) +
		m_offset / sizeof(*link);
		first_page->freelist = link->next;
		memset(link, POISON_INUSE, sizeof(*link));
		kunmap_atomic(link);

		first_page->inuse++;
		/* Now move the zspage to another fullness group, if required */
		fix_fullness_group(pool, first_page);
		spin_unlock(&class->lock);

		return obj;
		}
		EXPORT_SYMBOL_GPL(zs_malloc);

		void zs_free(struct zs_pool pool, void obj)
		{
		struct link_free *link;
		struct page first_page, f_page;
		unsigned long f_objidx, f_offset;

		int class_idx;
		struct size_class *class;
		enum fullness_group fullness;

		if (unlikely(!obj))
		return;

		obj_handle_to_location(obj, &f_page, &f_objidx);
		first_page = get_first_page(f_page);

		get_zspage_mapping(first_page, &class_idx, &fullness);
		class = &pool->size_class[class_idx];
		f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);

		spin_lock(&class->lock);

		/* Insert this object in containing zspage's freelist */
		link = (struct link_free )((unsigned char )kmap_atomic(f_page)
		+ f_offset);
		link->next = first_page->freelist;
		kunmap_atomic(link);
		first_page->freelist = obj;

		first_page->inuse--;
		fullness = fix_fullness_group(pool, first_page);

		if (fullness == ZS_EMPTY)
		class->pages_allocated -= class->zspage_order;

		spin_unlock(&class->lock);

		if (fullness == ZS_EMPTY)
		free_zspage(first_page);
		}
		EXPORT_SYMBOL_GPL(zs_free);

		void zs_map_object(struct zs_pool pool, void *handle)
		{
		struct page *page;
		unsigned long obj_idx, off;

		unsigned int class_idx;
		enum fullness_group fg;
		struct size_class *class;
		struct mapping_area *area;

		BUG_ON(!handle);

		obj_handle_to_location(handle, &page, &obj_idx);
		get_zspage_mapping(get_first_page(page), &class_idx, &fg);
		class = &pool->size_class[class_idx];
		off = obj_idx_to_offset(page, obj_idx, class->size);

		area = &get_cpu_var(zs_map_area);
		if (off + class->size <= PAGE_SIZE) {
		/* this object is contained entirely within a page */
		area->vm_addr = kmap_atomic(page);
		} else {
		/* this object spans two pages */
		struct page *nextp;

		nextp = get_next_page(page);
		BUG_ON(!nextp);


		set_pte(area->vm_ptes[0], mk_pte(page, PAGE_KERNEL));
		set_pte(area->vm_ptes[1], mk_pte(nextp, PAGE_KERNEL));

		/* We pre-allocated VM area so mapping can never fail */
		area->vm_addr = area->vm->addr;
		}

		return area->vm_addr + off;
		}
		EXPORT_SYMBOL_GPL(zs_map_object);

		void zs_unmap_object(struct zs_pool pool, void handle)
		{
		struct page *page;
		unsigned long obj_idx, off;

		unsigned int class_idx;
		enum fullness_group fg;
		struct size_class *class;
		struct mapping_area *area;

		BUG_ON(!handle);

		obj_handle_to_location(handle, &page, &obj_idx);
		get_zspage_mapping(get_first_page(page), &class_idx, &fg);
		class = &pool->size_class[class_idx];
		off = obj_idx_to_offset(page, obj_idx, class->size);

		area = &__get_cpu_var(zs_map_area);
		if (off + class->size <= PAGE_SIZE) {
		kunmap_atomic(area->vm_addr);
		} else {
		set_pte(area->vm_ptes[0], __pte(0));
		set_pte(area->vm_ptes[1], __pte(0));
		__flush_tlb_one((unsigned long)area->vm_addr);
		__flush_tlb_one((unsigned long)area->vm_addr + PAGE_SIZE);
		}
		put_cpu_var(zs_map_area);
		}
		EXPORT_SYMBOL_GPL(zs_unmap_object);

		u64 zs_get_total_size_bytes(struct zs_pool *pool)
		{
		int i;
		u64 npages = 0;

		for (i = 0; i < ZS_SIZE_CLASSES; i++)
		npages += pool->size_class[i].pages_allocated;

		return npages << PAGE_SHIFT;
		}
		EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);

drivers/staging/zsmalloc/zsmalloc.h

0 → 100644

+31 −0

Original line number	Diff line number	Diff line
		/*
		* zsmalloc memory allocator
		*
		* Copyright (C) 2011 Nitin Gupta
		*
		* This code is released using a dual license strategy: BSD/GPL
		* You can choose the license that better fits your requirements.
		*
		* Released under the terms of 3-clause BSD License
		* Released under the terms of GNU General Public License Version 2.0
		*/

		#ifndef _ZS_MALLOC_H_
		#define _ZS_MALLOC_H_

		#include <linux/types.h>

		struct zs_pool;

		struct zs_pool zs_create_pool(const char name, gfp_t flags);
		void zs_destroy_pool(struct zs_pool *pool);

		void zs_malloc(struct zs_pool pool, size_t size);
		void zs_free(struct zs_pool pool, void obj);

		void zs_map_object(struct zs_pool pool, void *handle);
		void zs_unmap_object(struct zs_pool pool, void handle);

		u64 zs_get_total_size_bytes(struct zs_pool *pool);

		#endif

drivers/staging/zsmalloc/zsmalloc_int.h

0 → 100644

+126 −0

Original line number	Diff line number	Diff line
		/*
		* zsmalloc memory allocator
		*
		* Copyright (C) 2011 Nitin Gupta
		*
		* This code is released using a dual license strategy: BSD/GPL
		* You can choose the license that better fits your requirements.
		*
		* Released under the terms of 3-clause BSD License
		* Released under the terms of GNU General Public License Version 2.0
		*/

		#ifndef _ZS_MALLOC_INT_H_
		#define _ZS_MALLOC_INT_H_

		#include <linux/kernel.h>
		#include <linux/spinlock.h>
		#include <linux/types.h>

		/*
		* This must be power of 2 and greater than of equal to sizeof(link_free).
		* These two conditions ensure that any 'struct link_free' itself doesn't
		* span more than 1 page which avoids complex case of mapping 2 pages simply
		* to restore link_free pointer values.
		*/
		#define ZS_ALIGN 8

		/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
		#define ZS_MIN_ALLOC_SIZE 32
		#define ZS_MAX_ALLOC_SIZE PAGE_SIZE

		/*
		* On systems with 4K page size, this gives 254 size classes! There is a
		* trader-off here:
		* - Large number of size classes is potentially wasteful as free page are
		* spread across these classes
		* - Small number of size classes causes large internal fragmentation
		* - Probably its better to use specific size classes (empirically
		* determined). NOTE: all those class sizes must be set as multiple of
		* ZS_ALIGN to make sure link_free itself never has to span 2 pages.
		*
		* ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
		* (reason above)
		*/
		#define ZS_SIZE_CLASS_DELTA 16
		#define ZS_SIZE_CLASSES ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \
		ZS_SIZE_CLASS_DELTA + 1)

		/*
		* A single 'zspage' is composed of N discontiguous 0-order (single) pages.
		* This defines upper limit on N.
		*/
		static const int max_zspage_order = 4;

		/*
		* We do not maintain any list for completely empty or full pages
		*/
		enum fullness_group {
		ZS_ALMOST_FULL,
		ZS_ALMOST_EMPTY,
		_ZS_NR_FULLNESS_GROUPS,

		ZS_EMPTY,
		ZS_FULL
		};

		/*
		* We assign a page to ZS_ALMOST_EMPTY fullness group when:
		* n <= N / f, where
		* n = number of allocated objects
		* N = total number of objects zspage can store
		* f = 1/fullness_threshold_frac
		*
		* Similarly, we assign zspage to:
		* ZS_ALMOST_FULL when n > N / f
		* ZS_EMPTY when n == 0
		* ZS_FULL when n == N
		*
		* (see: fix_fullness_group())
		*/
		static const int fullness_threshold_frac = 4;

		struct mapping_area {
		struct vm_struct *vm;
		pte_t *vm_ptes[2];
		char *vm_addr;
		};

		struct size_class {
		/*
		* Size of objects stored in this class. Must be multiple
		* of ZS_ALIGN.
		*/
		int size;
		unsigned int index;

		/* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
		int zspage_order;

		spinlock_t lock;

		/* stats */
		u64 pages_allocated;

		struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
		};

		/*
		* Placed within free objects to form a singly linked list.
		* For every zspage, first_page->freelist gives head of this list.
		*
		* This must be power of 2 and less than or equal to ZS_ALIGN
		*/
		struct link_free {
		/* Handle of next free chunk (encodes <PFN, obj_idx>) */
		void *next;
		};

		struct zs_pool {
		struct size_class size_class[ZS_SIZE_CLASSES];

		gfp_t flags; /* allocation flags used when growing pool */
		const char *name;
		};

		#endif