drivers/staging/zcache/zcache-main.c: fix build

[deliverable/linux.git] / drivers / staging / zcache / zcache-main.c

/*
 * zcache.c
 *
 * Copyright (c) 2010-2012, Dan Magenheimer, Oracle Corp.
 * Copyright (c) 2010,2011, Nitin Gupta
 *
 * Zcache provides an in-kernel "host implementation" for transcendent memory
 * ("tmem") and, thus indirectly, for cleancache and frontswap.  Zcache uses
 * lzo1x compression to improve density and an embedded allocator called
 * "zbud" which "buddies" two compressed pages semi-optimally in each physical
 * pageframe.  Zbud is integrally tied into tmem to allow pageframes to
 * be "reclaimed" efficiently.
 */

#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/atomic.h>
#include <linux/math64.h>
#include <linux/crypto.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>

#include <linux/cleancache.h>
#include <linux/frontswap.h>
#include "tmem.h"
#include "zcache.h"
#include "zbud.h"
#include "ramster.h"
#include "debug.h"
#ifdef CONFIG_RAMSTER
static bool ramster_enabled __read_mostly;
#else
#define ramster_enabled false
#endif

#ifndef __PG_WAS_ACTIVE
static inline bool PageWasActive(struct page *page)
{
	return true;
}

static inline void SetPageWasActive(struct page *page)
{
}
#endif

#ifdef FRONTSWAP_HAS_EXCLUSIVE_GETS
static bool frontswap_has_exclusive_gets __read_mostly = true;
#else
static bool frontswap_has_exclusive_gets __read_mostly;
static inline void frontswap_tmem_exclusive_gets(bool b)
{
}
#endif

/* enable (or fix code) when Seth's patches are accepted upstream */
#define zcache_writeback_enabled 0

static bool zcache_enabled __read_mostly;
static bool disable_cleancache __read_mostly;
static bool disable_frontswap __read_mostly;
static bool disable_frontswap_ignore_nonactive __read_mostly;
static bool disable_cleancache_ignore_nonactive __read_mostly;
static char *namestr __read_mostly = "zcache";

#define ZCACHE_GFP_MASK \
	(__GFP_FS | __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC)

/* crypto API for zcache  */
#define ZCACHE_COMP_NAME_SZ CRYPTO_MAX_ALG_NAME
static char zcache_comp_name[ZCACHE_COMP_NAME_SZ] __read_mostly;
static struct crypto_comp * __percpu *zcache_comp_pcpu_tfms __read_mostly;

enum comp_op {
	ZCACHE_COMPOP_COMPRESS,
	ZCACHE_COMPOP_DECOMPRESS
};

static inline int zcache_comp_op(enum comp_op op,
				const u8 *src, unsigned int slen,
				u8 *dst, unsigned int *dlen)
{
	struct crypto_comp *tfm;
	int ret = -1;

	BUG_ON(!zcache_comp_pcpu_tfms);
	tfm = *per_cpu_ptr(zcache_comp_pcpu_tfms, get_cpu());
	BUG_ON(!tfm);
	switch (op) {
	case ZCACHE_COMPOP_COMPRESS:
		ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
		break;
	case ZCACHE_COMPOP_DECOMPRESS:
		ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
		break;
	default:
		ret = -EINVAL;
	}
	put_cpu();
	return ret;
}

/*
 * policy parameters
 */

/*
 * byte count defining poor compression; pages with greater zsize will be
 * rejected
 */
static unsigned int zbud_max_zsize __read_mostly = (PAGE_SIZE / 8) * 7;
/*
 * byte count defining poor *mean* compression; pages with greater zsize
 * will be rejected until sufficient better-compressed pages are accepted
 * driving the mean below this threshold
 */
static unsigned int zbud_max_mean_zsize __read_mostly = (PAGE_SIZE / 8) * 5;

/*
 * for now, used named slabs so can easily track usage; later can
 * either just use kmalloc, or perhaps add a slab-like allocator
 * to more carefully manage total memory utilization
 */
static struct kmem_cache *zcache_objnode_cache;
static struct kmem_cache *zcache_obj_cache;

static DEFINE_PER_CPU(struct zcache_preload, zcache_preloads) = { 0, };

/* Used by debug.c */
ssize_t zcache_pers_zpages;
u64 zcache_pers_zbytes;
ssize_t zcache_eph_pageframes;
ssize_t zcache_pers_pageframes;

/* Used by this code. */
ssize_t zcache_last_active_file_pageframes;
ssize_t zcache_last_inactive_file_pageframes;
ssize_t zcache_last_active_anon_pageframes;
ssize_t zcache_last_inactive_anon_pageframes;
#ifdef CONFIG_ZCACHE_WRITEBACK
ssize_t zcache_writtenback_pages;
ssize_t zcache_outstanding_writeback_pages;
#endif
/*
 * zcache core code starts here
 */

static struct zcache_client zcache_host;
static struct zcache_client zcache_clients[MAX_CLIENTS];

static inline bool is_local_client(struct zcache_client *cli)
{
	return cli == &zcache_host;
}

static struct zcache_client *zcache_get_client_by_id(uint16_t cli_id)
{
	struct zcache_client *cli = &zcache_host;

	if (cli_id != LOCAL_CLIENT) {
		if (cli_id >= MAX_CLIENTS)
			goto out;
		cli = &zcache_clients[cli_id];
	}
out:
	return cli;
}

/*
 * Tmem operations assume the poolid implies the invoking client.
 * Zcache only has one client (the kernel itself): LOCAL_CLIENT.
 * RAMster has each client numbered by cluster node, and a KVM version
 * of zcache would have one client per guest and each client might
 * have a poolid==N.
 */
struct tmem_pool *zcache_get_pool_by_id(uint16_t cli_id, uint16_t poolid)
{
	struct tmem_pool *pool = NULL;
	struct zcache_client *cli = NULL;

	cli = zcache_get_client_by_id(cli_id);
	if (cli == NULL)
		goto out;
	if (!is_local_client(cli))
		atomic_inc(&cli->refcount);
	if (poolid < MAX_POOLS_PER_CLIENT) {
		pool = cli->tmem_pools[poolid];
		if (pool != NULL)
			atomic_inc(&pool->refcount);
	}
out:
	return pool;
}

void zcache_put_pool(struct tmem_pool *pool)
{
	struct zcache_client *cli = NULL;

	if (pool == NULL)
		BUG();
	cli = pool->client;
	atomic_dec(&pool->refcount);
	if (!is_local_client(cli))
		atomic_dec(&cli->refcount);
}

int zcache_new_client(uint16_t cli_id)
{
	struct zcache_client *cli;
	int ret = -1;

	cli = zcache_get_client_by_id(cli_id);
	if (cli == NULL)
		goto out;
	if (cli->allocated)
		goto out;
	cli->allocated = 1;
	ret = 0;
out:
	return ret;
}

/*
 * zcache implementation for tmem host ops
 */

static struct tmem_objnode *zcache_objnode_alloc(struct tmem_pool *pool)
{
	struct tmem_objnode *objnode = NULL;
	struct zcache_preload *kp;
	int i;

	kp = &__get_cpu_var(zcache_preloads);
	for (i = 0; i < ARRAY_SIZE(kp->objnodes); i++) {
		objnode = kp->objnodes[i];
		if (objnode != NULL) {
			kp->objnodes[i] = NULL;
			break;
		}
	}
	BUG_ON(objnode == NULL);
	inc_zcache_objnode_count();
	return objnode;
}

static void zcache_objnode_free(struct tmem_objnode *objnode,
					struct tmem_pool *pool)
{
	dec_zcache_objnode_count();
	kmem_cache_free(zcache_objnode_cache, objnode);
}

static struct tmem_obj *zcache_obj_alloc(struct tmem_pool *pool)
{
	struct tmem_obj *obj = NULL;
	struct zcache_preload *kp;

	kp = &__get_cpu_var(zcache_preloads);
	obj = kp->obj;
	BUG_ON(obj == NULL);
	kp->obj = NULL;
	inc_zcache_obj_count();
	return obj;
}

static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool)
{
	dec_zcache_obj_count();
	kmem_cache_free(zcache_obj_cache, obj);
}

static struct tmem_hostops zcache_hostops = {
	.obj_alloc = zcache_obj_alloc,
	.obj_free = zcache_obj_free,
	.objnode_alloc = zcache_objnode_alloc,
	.objnode_free = zcache_objnode_free,
};

static struct page *zcache_alloc_page(void)
{
	struct page *page = alloc_page(ZCACHE_GFP_MASK);

	if (page != NULL)
		inc_zcache_pageframes_alloced();
	return page;
}

static void zcache_free_page(struct page *page)
{
	long curr_pageframes;
	static long max_pageframes, min_pageframes;

	if (page == NULL)
		BUG();
	__free_page(page);
	inc_zcache_pageframes_freed();
	curr_pageframes = curr_pageframes_count();
	if (curr_pageframes > max_pageframes)
		max_pageframes = curr_pageframes;
	if (curr_pageframes < min_pageframes)
		min_pageframes = curr_pageframes;
#ifdef CONFIG_ZCACHE_DEBUG
	if (curr_pageframes > 2L || curr_pageframes < -2L) {
		/* pr_info here */
	}
#endif
}

/*
 * zcache implementations for PAM page descriptor ops
 */

/* forward reference */
static void zcache_compress(struct page *from,
				void **out_va, unsigned *out_len);

static struct page *zcache_evict_eph_pageframe(void);

static void *zcache_pampd_eph_create(char *data, size_t size, bool raw,
					struct tmem_handle *th)
{
	void *pampd = NULL, *cdata = data;
	unsigned clen = size;
	struct page *page = (struct page *)(data), *newpage;

	if (!raw) {
		zcache_compress(page, &cdata, &clen);
		if (clen > zbud_max_buddy_size()) {
			inc_zcache_compress_poor();
			goto out;
		}
	} else {
		BUG_ON(clen > zbud_max_buddy_size());
	}

	/* look for space via an existing match first */
	pampd = (void *)zbud_match_prep(th, true, cdata, clen);
	if (pampd != NULL)
		goto got_pampd;

	/* no match, now we need to find (or free up) a full page */
	newpage = zcache_alloc_page();
	if (newpage != NULL)
		goto create_in_new_page;

	inc_zcache_failed_getfreepages();
	/* can't allocate a page, evict an ephemeral page via LRU */
	newpage = zcache_evict_eph_pageframe();
	if (newpage == NULL) {
		inc_zcache_eph_ate_tail_failed();
		goto out;
	}
	inc_zcache_eph_ate_tail();

create_in_new_page:
	pampd = (void *)zbud_create_prep(th, true, cdata, clen, newpage);
	BUG_ON(pampd == NULL);
	inc_zcache_eph_pageframes();

got_pampd:
	inc_zcache_eph_zbytes(clen);
	inc_zcache_eph_zpages();
	if (ramster_enabled && raw)
		ramster_count_foreign_pages(true, 1);
out:
	return pampd;
}

static void *zcache_pampd_pers_create(char *data, size_t size, bool raw,
					struct tmem_handle *th)
{
	void *pampd = NULL, *cdata = data;
	unsigned clen = size;
	struct page *page = (struct page *)(data), *newpage;
	unsigned long zbud_mean_zsize;
	unsigned long curr_pers_zpages, total_zsize;

	if (data == NULL) {
		BUG_ON(!ramster_enabled);
		goto create_pampd;
	}
	curr_pers_zpages = zcache_pers_zpages;
/* FIXME CONFIG_RAMSTER... subtract atomic remote_pers_pages here? */
	if (!raw)
		zcache_compress(page, &cdata, &clen);
	/* reject if compression is too poor */
	if (clen > zbud_max_zsize) {
		inc_zcache_compress_poor();
		goto out;
	}
	/* reject if mean compression is too poor */
	if ((clen > zbud_max_mean_zsize) && (curr_pers_zpages > 0)) {
		total_zsize = zcache_pers_zbytes;
		if ((long)total_zsize < 0)
			total_zsize = 0;
		zbud_mean_zsize = div_u64(total_zsize,
					curr_pers_zpages);
		if (zbud_mean_zsize > zbud_max_mean_zsize) {
			inc_zcache_mean_compress_poor();
			goto out;
		}
	}

create_pampd:
	/* look for space via an existing match first */
	pampd = (void *)zbud_match_prep(th, false, cdata, clen);
	if (pampd != NULL)
		goto got_pampd;

	/* no match, now we need to find (or free up) a full page */
	newpage = zcache_alloc_page();
	if (newpage != NULL)
		goto create_in_new_page;
	/*
	 * FIXME do the following only if eph is oversized?
	 * if (zcache_eph_pageframes >
	 * (global_page_state(NR_LRU_BASE + LRU_ACTIVE_FILE) +
	 * global_page_state(NR_LRU_BASE + LRU_INACTIVE_FILE)))
	 */
	inc_zcache_failed_getfreepages();
	/* can't allocate a page, evict an ephemeral page via LRU */
	newpage = zcache_evict_eph_pageframe();
	if (newpage == NULL) {
		inc_zcache_pers_ate_eph_failed();
		goto out;
	}
	inc_zcache_pers_ate_eph();

create_in_new_page:
	pampd = (void *)zbud_create_prep(th, false, cdata, clen, newpage);
	BUG_ON(pampd == NULL);
	inc_zcache_pers_pageframes();

got_pampd:
	inc_zcache_pers_zpages();
	inc_zcache_pers_zbytes(clen);
	if (ramster_enabled && raw)
		ramster_count_foreign_pages(false, 1);
out:
	return pampd;
}

/*
 * This is called directly from zcache_put_page to pre-allocate space
 * to store a zpage.
 */
void *zcache_pampd_create(char *data, unsigned int size, bool raw,
					int eph, struct tmem_handle *th)
{
	void *pampd = NULL;
	struct zcache_preload *kp;
	struct tmem_objnode *objnode;
	struct tmem_obj *obj;
	int i;

	BUG_ON(!irqs_disabled());
	/* pre-allocate per-cpu metadata */
	BUG_ON(zcache_objnode_cache == NULL);
	BUG_ON(zcache_obj_cache == NULL);
	kp = &__get_cpu_var(zcache_preloads);
	for (i = 0; i < ARRAY_SIZE(kp->objnodes); i++) {
		objnode = kp->objnodes[i];
		if (objnode == NULL) {
			objnode = kmem_cache_alloc(zcache_objnode_cache,
							ZCACHE_GFP_MASK);
			if (unlikely(objnode == NULL)) {
				inc_zcache_failed_alloc();
				goto out;
			}
			kp->objnodes[i] = objnode;
		}
	}
	if (kp->obj == NULL) {
		obj = kmem_cache_alloc(zcache_obj_cache, ZCACHE_GFP_MASK);
		kp->obj = obj;
	}
	if (unlikely(kp->obj == NULL)) {
		inc_zcache_failed_alloc();
		goto out;
	}
	/*
	 * ok, have all the metadata pre-allocated, now do the data
	 * but since how we allocate the data is dependent on ephemeral
	 * or persistent, we split the call here to different sub-functions
	 */
	if (eph)
		pampd = zcache_pampd_eph_create(data, size, raw, th);
	else
		pampd = zcache_pampd_pers_create(data, size, raw, th);
out:
	return pampd;
}

/*
 * This is a pamops called via tmem_put and is necessary to "finish"
 * a pampd creation.
 */
void zcache_pampd_create_finish(void *pampd, bool eph)
{
	zbud_create_finish((struct zbudref *)pampd, eph);
}

/*
 * This is passed as a function parameter to zbud_decompress so that
 * zbud need not be familiar with the details of crypto. It assumes that
 * the bytes from_va and to_va through from_va+size-1 and to_va+size-1 are
 * kmapped.  It must be successful, else there is a logic bug somewhere.
 */
static void zcache_decompress(char *from_va, unsigned int size, char *to_va)
{
	int ret;
	unsigned int outlen = PAGE_SIZE;

	ret = zcache_comp_op(ZCACHE_COMPOP_DECOMPRESS, from_va, size,
				to_va, &outlen);
	BUG_ON(ret);
	BUG_ON(outlen != PAGE_SIZE);
}

/*
 * Decompress from the kernel va to a pageframe
 */
void zcache_decompress_to_page(char *from_va, unsigned int size,
					struct page *to_page)
{
	char *to_va = kmap_atomic(to_page);
	zcache_decompress(from_va, size, to_va);
	kunmap_atomic(to_va);
}

/*
 * fill the pageframe corresponding to the struct page with the data
 * from the passed pampd
 */
static int zcache_pampd_get_data(char *data, size_t *sizep, bool raw,
					void *pampd, struct tmem_pool *pool,
					struct tmem_oid *oid, uint32_t index)
{
	int ret;
	bool eph = !is_persistent(pool);

	BUG_ON(preemptible());
	BUG_ON(eph);	/* fix later if shared pools get implemented */
	BUG_ON(pampd_is_remote(pampd));
	if (raw)
		ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd,
						sizep, eph);
	else {
		ret = zbud_decompress((struct page *)(data),
					(struct zbudref *)pampd, false,
					zcache_decompress);
		*sizep = PAGE_SIZE;
	}
	return ret;
}

/*
 * fill the pageframe corresponding to the struct page with the data
 * from the passed pampd
 */
static int zcache_pampd_get_data_and_free(char *data, size_t *sizep, bool raw,
					void *pampd, struct tmem_pool *pool,
					struct tmem_oid *oid, uint32_t index)
{
	int ret;
	bool eph = !is_persistent(pool);
	struct page *page = NULL;
	unsigned int zsize, zpages;

	BUG_ON(preemptible());
	BUG_ON(pampd_is_remote(pampd));
	if (raw)
		ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd,
						sizep, eph);
	else {
		ret = zbud_decompress((struct page *)(data),
					(struct zbudref *)pampd, eph,
					zcache_decompress);
		*sizep = PAGE_SIZE;
	}
	page = zbud_free_and_delist((struct zbudref *)pampd, eph,
					&zsize, &zpages);
	if (eph) {
		if (page)
			dec_zcache_eph_pageframes();
		dec_zcache_eph_zpages(zpages);
		dec_zcache_eph_zbytes(zsize);
	} else {
		if (page)
			dec_zcache_pers_pageframes();
		dec_zcache_pers_zpages(zpages);
		dec_zcache_pers_zbytes(zsize);
	}
	if (!is_local_client(pool->client))
		ramster_count_foreign_pages(eph, -1);
	if (page)
		zcache_free_page(page);
	return ret;
}

/*
 * free the pampd and remove it from any zcache lists
 * pampd must no longer be pointed to from any tmem data structures!
 */
static void zcache_pampd_free(void *pampd, struct tmem_pool *pool,
			      struct tmem_oid *oid, uint32_t index, bool acct)
{
	struct page *page = NULL;
	unsigned int zsize, zpages;

	BUG_ON(preemptible());
	if (pampd_is_remote(pampd)) {
		BUG_ON(!ramster_enabled);
		pampd = ramster_pampd_free(pampd, pool, oid, index, acct);
		if (pampd == NULL)
			return;
	}
	if (is_ephemeral(pool)) {
		page = zbud_free_and_delist((struct zbudref *)pampd,
						true, &zsize, &zpages);
		if (page)
			dec_zcache_eph_pageframes();
		dec_zcache_eph_zpages(zpages);
		dec_zcache_eph_zbytes(zsize);
		/* FIXME CONFIG_RAMSTER... check acct parameter? */
	} else {
		page = zbud_free_and_delist((struct zbudref *)pampd,
						false, &zsize, &zpages);
		if (page)
			dec_zcache_pers_pageframes();
		dec_zcache_pers_zpages(zpages);
		dec_zcache_pers_zbytes(zsize);
	}
	if (!is_local_client(pool->client))
		ramster_count_foreign_pages(is_ephemeral(pool), -1);
	if (page)
		zcache_free_page(page);
}

static struct tmem_pamops zcache_pamops = {
	.create_finish = zcache_pampd_create_finish,
	.get_data = zcache_pampd_get_data,
	.get_data_and_free = zcache_pampd_get_data_and_free,
	.free = zcache_pampd_free,
};

/*
 * zcache compression/decompression and related per-cpu stuff
 */

static DEFINE_PER_CPU(unsigned char *, zcache_dstmem);
#define ZCACHE_DSTMEM_ORDER 1

static void zcache_compress(struct page *from, void **out_va, unsigned *out_len)
{
	int ret;
	unsigned char *dmem = __get_cpu_var(zcache_dstmem);
	char *from_va;

	BUG_ON(!irqs_disabled());
	/* no buffer or no compressor so can't compress */
	BUG_ON(dmem == NULL);
	*out_len = PAGE_SIZE << ZCACHE_DSTMEM_ORDER;
	from_va = kmap_atomic(from);
	mb();
	ret = zcache_comp_op(ZCACHE_COMPOP_COMPRESS, from_va, PAGE_SIZE, dmem,
				out_len);
	BUG_ON(ret);
	*out_va = dmem;
	kunmap_atomic(from_va);
}

static int zcache_comp_cpu_up(int cpu)
{
	struct crypto_comp *tfm;

	tfm = crypto_alloc_comp(zcache_comp_name, 0, 0);
	if (IS_ERR(tfm))
		return NOTIFY_BAD;
	*per_cpu_ptr(zcache_comp_pcpu_tfms, cpu) = tfm;
	return NOTIFY_OK;
}

static void zcache_comp_cpu_down(int cpu)
{
	struct crypto_comp *tfm;

	tfm = *per_cpu_ptr(zcache_comp_pcpu_tfms, cpu);
	crypto_free_comp(tfm);
	*per_cpu_ptr(zcache_comp_pcpu_tfms, cpu) = NULL;
}

static int zcache_cpu_notifier(struct notifier_block *nb,
				unsigned long action, void *pcpu)
{
	int ret, i, cpu = (long)pcpu;
	struct zcache_preload *kp;

	switch (action) {
	case CPU_UP_PREPARE:
		ret = zcache_comp_cpu_up(cpu);
		if (ret != NOTIFY_OK) {
			pr_err("%s: can't allocate compressor xform\n",
				namestr);
			return ret;
		}
		per_cpu(zcache_dstmem, cpu) = (void *)__get_free_pages(
			GFP_KERNEL | __GFP_REPEAT, ZCACHE_DSTMEM_ORDER);
		if (ramster_enabled)
			ramster_cpu_up(cpu);
		break;
	case CPU_DEAD:
	case CPU_UP_CANCELED:
		zcache_comp_cpu_down(cpu);
		free_pages((unsigned long)per_cpu(zcache_dstmem, cpu),
			ZCACHE_DSTMEM_ORDER);
		per_cpu(zcache_dstmem, cpu) = NULL;
		kp = &per_cpu(zcache_preloads, cpu);
		for (i = 0; i < ARRAY_SIZE(kp->objnodes); i++) {
			if (kp->objnodes[i])
				kmem_cache_free(zcache_objnode_cache,
						kp->objnodes[i]);
		}
		if (kp->obj) {
			kmem_cache_free(zcache_obj_cache, kp->obj);
			kp->obj = NULL;
		}
		if (ramster_enabled)
			ramster_cpu_down(cpu);
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

static struct notifier_block zcache_cpu_notifier_block = {
	.notifier_call = zcache_cpu_notifier
};

/*
 * The following code interacts with the zbud eviction and zbud
 * zombify code to access LRU pages
 */

static struct page *zcache_evict_eph_pageframe(void)
{
	struct page *page;
	unsigned int zsize = 0, zpages = 0;

	page = zbud_evict_pageframe_lru(&zsize, &zpages);
	if (page == NULL)
		goto out;
	dec_zcache_eph_zbytes(zsize);
	dec_zcache_eph_zpages(zpages);
	inc_zcache_evicted_eph_zpages(zpages);
	dec_zcache_eph_pageframes();
	inc_zcache_evicted_eph_pageframes();
out:
	return page;
}

#ifdef CONFIG_ZCACHE_WRITEBACK

static atomic_t zcache_outstanding_writeback_pages_atomic = ATOMIC_INIT(0);

static inline void inc_zcache_outstanding_writeback_pages(void)
{
	zcache_outstanding_writeback_pages =
	    atomic_inc_return(&zcache_outstanding_writeback_pages_atomic);
}
static inline void dec_zcache_outstanding_writeback_pages(void)
{
	zcache_outstanding_writeback_pages =
	  atomic_dec_return(&zcache_outstanding_writeback_pages_atomic);
};
static void unswiz(struct tmem_oid oid, u32 index,
				unsigned *type, pgoff_t *offset);

/*
 *  Choose an LRU persistent pageframe and attempt to write it back to
 *  the backing swap disk by calling frontswap_writeback on both zpages.
 *
 *  This is work-in-progress.
 */

static void zcache_end_swap_write(struct bio *bio, int err)
{
	end_swap_bio_write(bio, err);
	dec_zcache_outstanding_writeback_pages();
	zcache_writtenback_pages++;
}

/*
 * zcache_get_swap_cache_page
 *
 * This is an adaption of read_swap_cache_async()
 *
 * If success, page is returned in retpage
 * Returns 0 if page was already in the swap cache, page is not locked
 * Returns 1 if the new page needs to be populated, page is locked
 */
static int zcache_get_swap_cache_page(int type, pgoff_t offset,
				struct page *new_page)
{
	struct page *found_page;
	swp_entry_t entry = swp_entry(type, offset);
	int err;

	BUG_ON(new_page == NULL);
	do {
		/*
		 * First check the swap cache.  Since this is normally
		 * called after lookup_swap_cache() failed, re-calling
		 * that would confuse statistics.
		 */
		found_page = find_get_page(&swapper_space, entry.val);
		if (found_page)
			return 0;

		/*
		 * call radix_tree_preload() while we can wait.
		 */
		err = radix_tree_preload(GFP_KERNEL);
		if (err)
			break;

		/*
		 * Swap entry may have been freed since our caller observed it.
		 */
		err = swapcache_prepare(entry);
		if (err == -EEXIST) { /* seems racy */
			radix_tree_preload_end();
			continue;
		}
		if (err) { /* swp entry is obsolete ? */
			radix_tree_preload_end();
			break;
		}

		/* May fail (-ENOMEM) if radix-tree node allocation failed. */
		__set_page_locked(new_page);
		SetPageSwapBacked(new_page);
		err = __add_to_swap_cache(new_page, entry);
		if (likely(!err)) {
			radix_tree_preload_end();
			lru_cache_add_anon(new_page);
			return 1;
		}
		radix_tree_preload_end();
		ClearPageSwapBacked(new_page);
		__clear_page_locked(new_page);
		/*
		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
		 * clear SWAP_HAS_CACHE flag.
		 */
		swapcache_free(entry, NULL);
		/* FIXME: is it possible to get here without err==-ENOMEM?
		 * If not, we can dispense with the do loop, use goto retry */
	} while (err != -ENOMEM);

	return -ENOMEM;
}

/*
 * Given a frontswap zpage in zcache (identified by type/offset) and
 * an empty page, put the page into the swap cache, use frontswap
 * to get the page from zcache into the empty page, then give it
 * to the swap subsystem to send to disk (carefully avoiding the
 * possibility that frontswap might snatch it back).
 * Returns < 0 if error, 0 if successful, and 1 if successful but
 * the newpage passed in not needed and should be freed.
 */
static int zcache_frontswap_writeback_zpage(int type, pgoff_t offset,
					struct page *newpage)
{
	struct page *page = newpage;
	int ret;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_NONE,
	};

	ret = zcache_get_swap_cache_page(type, offset, page);
	if (ret < 0)
		return ret;
	else if (ret == 0) {
		/* more uptodate page is already in swapcache */
		__frontswap_invalidate_page(type, offset);
		return 1;
	}

	BUG_ON(!frontswap_has_exclusive_gets); /* load must also invalidate */
	/* FIXME: how is it possible to get here when page is unlocked? */
	__frontswap_load(page);
	SetPageUptodate(page);  /* above does SetPageDirty, is that enough? */

	/* start writeback */
	SetPageReclaim(page);
	/*
	 * Return value is ignored here because it doesn't change anything
	 * for us.  Page is returned unlocked.
	 */
	(void)__swap_writepage(page, &wbc, zcache_end_swap_write);
	page_cache_release(page);
	inc_zcache_outstanding_writeback_pages();

	return 0;
}

/*
 * The following is still a magic number... we want to allow forward progress
 * for writeback because it clears out needed RAM when under pressure, but
 * we don't want to allow writeback to absorb and queue too many GFP_KERNEL
 * pages if the swap device is very slow.
 */
#define ZCACHE_MAX_OUTSTANDING_WRITEBACK_PAGES 6400

/*
 * Try to allocate two free pages, first using a non-aggressive alloc,
 * then by evicting zcache ephemeral (clean pagecache) pages, and last
 * by aggressive GFP_KERNEL alloc.  We allow zbud to choose a pageframe
 * consisting of 1-2 zbuds/zpages, then call the writeback_zpage helper
 * function above for each.
 */
static int zcache_frontswap_writeback(void)
{
	struct tmem_handle th[2];
	int ret = 0;
	int nzbuds, writeback_ret;
	unsigned type;
	struct page *znewpage1 = NULL, *znewpage2 = NULL;
	struct page *evictpage1 = NULL, *evictpage2 = NULL;
	struct page *newpage1 = NULL, *newpage2 = NULL;
	struct page *page1 = NULL, *page2 = NULL;
	pgoff_t offset;

	znewpage1 = alloc_page(ZCACHE_GFP_MASK);
	znewpage2 = alloc_page(ZCACHE_GFP_MASK);
	if (znewpage1 == NULL)
		evictpage1 = zcache_evict_eph_pageframe();
	if (znewpage2 == NULL)
		evictpage2 = zcache_evict_eph_pageframe();

	if ((evictpage1 == NULL || evictpage2 == NULL) &&
	    atomic_read(&zcache_outstanding_writeback_pages_atomic) >
				ZCACHE_MAX_OUTSTANDING_WRITEBACK_PAGES) {
		goto free_and_out;
	}
	if (znewpage1 == NULL && evictpage1 == NULL)
		newpage1 = alloc_page(GFP_KERNEL);
	if (znewpage2 == NULL && evictpage2 == NULL)
		newpage2 = alloc_page(GFP_KERNEL);
	if (newpage1 == NULL || newpage2 == NULL)
			goto free_and_out;

	/* ok, we have two pageframes pre-allocated, get a pair of zbuds */
	nzbuds = zbud_make_zombie_lru(&th[0], NULL, NULL, false);
	if (nzbuds == 0) {
		ret = -ENOENT;
		goto free_and_out;
	}

	/* process the first zbud */
	unswiz(th[0].oid, th[0].index, &type, &offset);
	page1 = (znewpage1 != NULL) ? znewpage1 :
			((newpage1 != NULL) ? newpage1 : evictpage1);
	writeback_ret = zcache_frontswap_writeback_zpage(type, offset, page1);
	if (writeback_ret < 0) {
		ret = -ENOMEM;
		goto free_and_out;
	}
	if (evictpage1 != NULL)
		zcache_pageframes_freed =
			atomic_inc_return(&zcache_pageframes_freed_atomic);
	if (writeback_ret == 0) {
		/* zcache_get_swap_cache_page will free, don't double free */
		znewpage1 = NULL;
		newpage1 = NULL;
		evictpage1 = NULL;
	}
	if (nzbuds < 2)
		goto free_and_out;

	/* if there is a second zbud, process it */
	unswiz(th[1].oid, th[1].index, &type, &offset);
	page2 = (znewpage2 != NULL) ? znewpage2 :
			((newpage2 != NULL) ? newpage2 : evictpage2);
	writeback_ret = zcache_frontswap_writeback_zpage(type, offset, page2);
	if (writeback_ret < 0) {
		ret = -ENOMEM;
		goto free_and_out;
	}
	if (evictpage2 != NULL)
		zcache_pageframes_freed =
			atomic_inc_return(&zcache_pageframes_freed_atomic);
	if (writeback_ret == 0) {
		znewpage2 = NULL;
		newpage2 = NULL;
		evictpage2 = NULL;
	}

free_and_out:
	if (znewpage1 != NULL)
		page_cache_release(znewpage1);
	if (znewpage2 != NULL)
		page_cache_release(znewpage2);
	if (newpage1 != NULL)
		page_cache_release(newpage1);
	if (newpage2 != NULL)
		page_cache_release(newpage2);
	if (evictpage1 != NULL)
		zcache_free_page(evictpage1);
	if (evictpage2 != NULL)
		zcache_free_page(evictpage2);
	return ret;
}
#endif /* CONFIG_ZCACHE_WRITEBACK */

/*
 * When zcache is disabled ("frozen"), pools can be created and destroyed,
 * but all puts (and thus all other operations that require memory allocation)
 * must fail.  If zcache is unfrozen, accepts puts, then frozen again,
 * data consistency requires all puts while frozen to be converted into
 * flushes.
 */
static bool zcache_freeze;

/*
 * This zcache shrinker interface reduces the number of ephemeral pageframes
 * used by zcache to approximately the same as the total number of LRU_FILE
 * pageframes in use, and now also reduces the number of persistent pageframes
 * used by zcache to approximately the same as the total number of LRU_ANON
 * pageframes in use.  FIXME POLICY: Probably the writeback should only occur
 * if the eviction doesn't free enough pages.
 */
static int shrink_zcache_memory(struct shrinker *shrink,
				struct shrink_control *sc)
{
	static bool in_progress;
	int ret = -1;
	int nr = sc->nr_to_scan;
	int nr_evict = 0;
	int nr_writeback = 0;
	struct page *page;
	int  file_pageframes_inuse, anon_pageframes_inuse;

	if (nr <= 0)
		goto skip_evict;

	/* don't allow more than one eviction thread at a time */
	if (in_progress)
		goto skip_evict;

	in_progress = true;

	/* we are going to ignore nr, and target a different value */
	zcache_last_active_file_pageframes =
		global_page_state(NR_LRU_BASE + LRU_ACTIVE_FILE);
	zcache_last_inactive_file_pageframes =
		global_page_state(NR_LRU_BASE + LRU_INACTIVE_FILE);
	file_pageframes_inuse = zcache_last_active_file_pageframes +
				zcache_last_inactive_file_pageframes;
	if (zcache_eph_pageframes > file_pageframes_inuse)
		nr_evict = zcache_eph_pageframes - file_pageframes_inuse;
	else
		nr_evict = 0;
	while (nr_evict-- > 0) {
		page = zcache_evict_eph_pageframe();
		if (page == NULL)
			break;
		zcache_free_page(page);
	}

	zcache_last_active_anon_pageframes =
		global_page_state(NR_LRU_BASE + LRU_ACTIVE_ANON);
	zcache_last_inactive_anon_pageframes =
		global_page_state(NR_LRU_BASE + LRU_INACTIVE_ANON);
	anon_pageframes_inuse = zcache_last_active_anon_pageframes +
				zcache_last_inactive_anon_pageframes;
	if (zcache_pers_pageframes > anon_pageframes_inuse)
		nr_writeback = zcache_pers_pageframes - anon_pageframes_inuse;
	else
		nr_writeback = 0;
	while (nr_writeback-- > 0) {
#ifdef CONFIG_ZCACHE_WRITEBACK
		int writeback_ret;
		writeback_ret = zcache_frontswap_writeback();
		if (writeback_ret == -ENOMEM)
#endif
			break;
	}
	in_progress = false;

skip_evict:
	/* resample: has changed, but maybe not all the way yet */
	zcache_last_active_file_pageframes =
		global_page_state(NR_LRU_BASE + LRU_ACTIVE_FILE);
	zcache_last_inactive_file_pageframes =
		global_page_state(NR_LRU_BASE + LRU_INACTIVE_FILE);
	ret = zcache_eph_pageframes - zcache_last_active_file_pageframes +
		zcache_last_inactive_file_pageframes;
	if (ret < 0)
		ret = 0;
	return ret;
}

static struct shrinker zcache_shrinker = {
	.shrink = shrink_zcache_memory,
	.seeks = DEFAULT_SEEKS,
};

/*
 * zcache shims between cleancache/frontswap ops and tmem
 */

/* FIXME rename these core routines to zcache_tmemput etc? */
int zcache_put_page(int cli_id, int pool_id, struct tmem_oid *oidp,
				uint32_t index, void *page,
				unsigned int size, bool raw, int ephemeral)
{
	struct tmem_pool *pool;
	struct tmem_handle th;
	int ret = -1;
	void *pampd = NULL;

	BUG_ON(!irqs_disabled());
	pool = zcache_get_pool_by_id(cli_id, pool_id);
	if (unlikely(pool == NULL))
		goto out;
	if (!zcache_freeze) {
		ret = 0;
		th.client_id = cli_id;
		th.pool_id = pool_id;
		th.oid = *oidp;
		th.index = index;
		pampd = zcache_pampd_create((char *)page, size, raw,
				ephemeral, &th);
		if (pampd == NULL) {
			ret = -ENOMEM;
			if (ephemeral)
				inc_zcache_failed_eph_puts();
			else
				inc_zcache_failed_pers_puts();
		} else {
			if (ramster_enabled)
				ramster_do_preload_flnode(pool);
			ret = tmem_put(pool, oidp, index, 0, pampd);
			if (ret < 0)
				BUG();
		}
		zcache_put_pool(pool);
	} else {
		inc_zcache_put_to_flush();
		if (ramster_enabled)
			ramster_do_preload_flnode(pool);
		if (atomic_read(&pool->obj_count) > 0)
			/* the put fails whether the flush succeeds or not */
			(void)tmem_flush_page(pool, oidp, index);
		zcache_put_pool(pool);
	}
out:
	return ret;
}

int zcache_get_page(int cli_id, int pool_id, struct tmem_oid *oidp,
				uint32_t index, void *page,
				size_t *sizep, bool raw, int get_and_free)
{
	struct tmem_pool *pool;
	int ret = -1;
	bool eph;

	if (!raw) {
		BUG_ON(irqs_disabled());
		BUG_ON(in_softirq());
	}
	pool = zcache_get_pool_by_id(cli_id, pool_id);
	eph = is_ephemeral(pool);
	if (likely(pool != NULL)) {
		if (atomic_read(&pool->obj_count) > 0)
			ret = tmem_get(pool, oidp, index, (char *)(page),
					sizep, raw, get_and_free);
		zcache_put_pool(pool);
	}
	WARN_ONCE((!is_ephemeral(pool) && (ret != 0)),
			"zcache_get fails on persistent pool, "
			"bad things are very likely to happen soon\n");
#ifdef RAMSTER_TESTING
	if (ret != 0 && ret != -1 && !(ret == -EINVAL && is_ephemeral(pool)))
		pr_err("TESTING zcache_get tmem_get returns ret=%d\n", ret);
#endif
	return ret;
}

int zcache_flush_page(int cli_id, int pool_id,
				struct tmem_oid *oidp, uint32_t index)
{
	struct tmem_pool *pool;
	int ret = -1;
	unsigned long flags;

	local_irq_save(flags);
	inc_zcache_flush_total();
	pool = zcache_get_pool_by_id(cli_id, pool_id);
	if (ramster_enabled)
		ramster_do_preload_flnode(pool);
	if (likely(pool != NULL)) {
		if (atomic_read(&pool->obj_count) > 0)
			ret = tmem_flush_page(pool, oidp, index);
		zcache_put_pool(pool);
	}
	if (ret >= 0)
		inc_zcache_flush_found();
	local_irq_restore(flags);
	return ret;
}

int zcache_flush_object(int cli_id, int pool_id,
				struct tmem_oid *oidp)
{
	struct tmem_pool *pool;
	int ret = -1;
	unsigned long flags;

	local_irq_save(flags);
	inc_zcache_flobj_total();
	pool = zcache_get_pool_by_id(cli_id, pool_id);
	if (ramster_enabled)
		ramster_do_preload_flnode(pool);
	if (likely(pool != NULL)) {
		if (atomic_read(&pool->obj_count) > 0)
			ret = tmem_flush_object(pool, oidp);
		zcache_put_pool(pool);
	}
	if (ret >= 0)
		inc_zcache_flobj_found();
	local_irq_restore(flags);
	return ret;
}

static int zcache_client_destroy_pool(int cli_id, int pool_id)
{
	struct tmem_pool *pool = NULL;
	struct zcache_client *cli = NULL;
	int ret = -1;

	if (pool_id < 0)
		goto out;
	if (cli_id == LOCAL_CLIENT)
		cli = &zcache_host;
	else if ((unsigned int)cli_id < MAX_CLIENTS)
		cli = &zcache_clients[cli_id];
	if (cli == NULL)
		goto out;
	atomic_inc(&cli->refcount);
	pool = cli->tmem_pools[pool_id];
	if (pool == NULL)
		goto out;
	cli->tmem_pools[pool_id] = NULL;
	/* wait for pool activity on other cpus to quiesce */
	while (atomic_read(&pool->refcount) != 0)
		;
	atomic_dec(&cli->refcount);
	local_bh_disable();
	ret = tmem_destroy_pool(pool);
	local_bh_enable();
	kfree(pool);
	if (cli_id == LOCAL_CLIENT)
		pr_info("%s: destroyed local pool id=%d\n", namestr, pool_id);
	else
		pr_info("%s: destroyed pool id=%d, client=%d\n",
				namestr, pool_id, cli_id);
out:
	return ret;
}

int zcache_new_pool(uint16_t cli_id, uint32_t flags)
{
	int poolid = -1;
	struct tmem_pool *pool;
	struct zcache_client *cli = NULL;

	if (cli_id == LOCAL_CLIENT)
		cli = &zcache_host;
	else if ((unsigned int)cli_id < MAX_CLIENTS)
		cli = &zcache_clients[cli_id];
	if (cli == NULL)
		goto out;
	atomic_inc(&cli->refcount);
	pool = kmalloc(sizeof(struct tmem_pool), GFP_ATOMIC);
	if (pool == NULL)
		goto out;

	for (poolid = 0; poolid < MAX_POOLS_PER_CLIENT; poolid++)
		if (cli->tmem_pools[poolid] == NULL)
			break;
	if (poolid >= MAX_POOLS_PER_CLIENT) {
		pr_info("%s: pool creation failed: max exceeded\n", namestr);
		kfree(pool);
		poolid = -1;
		goto out;
	}
	atomic_set(&pool->refcount, 0);
	pool->client = cli;
	pool->pool_id = poolid;
	tmem_new_pool(pool, flags);
	cli->tmem_pools[poolid] = pool;
	if (cli_id == LOCAL_CLIENT)
		pr_info("%s: created %s local tmem pool, id=%d\n", namestr,
			flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
			poolid);
	else
		pr_info("%s: created %s tmem pool, id=%d, client=%d\n", namestr,
			flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
			poolid, cli_id);
out:
	if (cli != NULL)
		atomic_dec(&cli->refcount);
	return poolid;
}

static int zcache_local_new_pool(uint32_t flags)
{
	return zcache_new_pool(LOCAL_CLIENT, flags);
}

int zcache_autocreate_pool(unsigned int cli_id, unsigned int pool_id, bool eph)
{
	struct tmem_pool *pool;
	struct zcache_client *cli;
	uint32_t flags = eph ? 0 : TMEM_POOL_PERSIST;
	int ret = -1;

	BUG_ON(!ramster_enabled);
	if (cli_id == LOCAL_CLIENT)
		goto out;
	if (pool_id >= MAX_POOLS_PER_CLIENT)
		goto out;
	if (cli_id >= MAX_CLIENTS)
		goto out;

	cli = &zcache_clients[cli_id];
	if ((eph && disable_cleancache) || (!eph && disable_frontswap)) {
		pr_err("zcache_autocreate_pool: pool type disabled\n");
		goto out;
	}
	if (!cli->allocated) {
		if (zcache_new_client(cli_id)) {
			pr_err("zcache_autocreate_pool: can't create client\n");
			goto out;
		}
		cli = &zcache_clients[cli_id];
	}
	atomic_inc(&cli->refcount);
	pool = cli->tmem_pools[pool_id];
	if (pool != NULL) {
		if (pool->persistent && eph) {
			pr_err("zcache_autocreate_pool: type mismatch\n");
			goto out;
		}
		ret = 0;
		goto out;
	}
	pool = kmalloc(sizeof(struct tmem_pool), GFP_KERNEL);
	if (pool == NULL)
		goto out;

	atomic_set(&pool->refcount, 0);
	pool->client = cli;
	pool->pool_id = pool_id;
	tmem_new_pool(pool, flags);
	cli->tmem_pools[pool_id] = pool;
	pr_info("%s: AUTOcreated %s tmem poolid=%d, for remote client=%d\n",
		namestr, flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
		pool_id, cli_id);
	ret = 0;
out:
	if (cli != NULL)
		atomic_dec(&cli->refcount);
	return ret;
}

/**********
 * Two kernel functionalities currently can be layered on top of tmem.
 * These are "cleancache" which is used as a second-chance cache for clean
 * page cache pages; and "frontswap" which is used for swap pages
 * to avoid writes to disk.  A generic "shim" is provided here for each
 * to translate in-kernel semantics to zcache semantics.
 */

static void zcache_cleancache_put_page(int pool_id,
					struct cleancache_filekey key,
					pgoff_t index, struct page *page)
{
	u32 ind = (u32) index;
	struct tmem_oid oid = *(struct tmem_oid *)&key;

	if (!disable_cleancache_ignore_nonactive && !PageWasActive(page)) {
		inc_zcache_eph_nonactive_puts_ignored();
		return;
	}
	if (likely(ind == index))
		(void)zcache_put_page(LOCAL_CLIENT, pool_id, &oid, index,
					page, PAGE_SIZE, false, 1);
}

static int zcache_cleancache_get_page(int pool_id,
					struct cleancache_filekey key,
					pgoff_t index, struct page *page)
{
	u32 ind = (u32) index;
	struct tmem_oid oid = *(struct tmem_oid *)&key;
	size_t size;
	int ret = -1;

	if (likely(ind == index)) {
		ret = zcache_get_page(LOCAL_CLIENT, pool_id, &oid, index,
					page, &size, false, 0);
		BUG_ON(ret >= 0 && size != PAGE_SIZE);
		if (ret == 0)
			SetPageWasActive(page);
	}
	return ret;
}

static void zcache_cleancache_flush_page(int pool_id,
					struct cleancache_filekey key,
					pgoff_t index)
{
	u32 ind = (u32) index;
	struct tmem_oid oid = *(struct tmem_oid *)&key;

	if (likely(ind == index))
		(void)zcache_flush_page(LOCAL_CLIENT, pool_id, &oid, ind);
}

static void zcache_cleancache_flush_inode(int pool_id,
					struct cleancache_filekey key)
{
	struct tmem_oid oid = *(struct tmem_oid *)&key;

	(void)zcache_flush_object(LOCAL_CLIENT, pool_id, &oid);
}

static void zcache_cleancache_flush_fs(int pool_id)
{
	if (pool_id >= 0)
		(void)zcache_client_destroy_pool(LOCAL_CLIENT, pool_id);
}

static int zcache_cleancache_init_fs(size_t pagesize)
{
	BUG_ON(sizeof(struct cleancache_filekey) !=
				sizeof(struct tmem_oid));
	BUG_ON(pagesize != PAGE_SIZE);
	return zcache_local_new_pool(0);
}

static int zcache_cleancache_init_shared_fs(char *uuid, size_t pagesize)
{
	/* shared pools are unsupported and map to private */
	BUG_ON(sizeof(struct cleancache_filekey) !=
				sizeof(struct tmem_oid));
	BUG_ON(pagesize != PAGE_SIZE);
	return zcache_local_new_pool(0);
}

static struct cleancache_ops zcache_cleancache_ops = {
	.put_page = zcache_cleancache_put_page,
	.get_page = zcache_cleancache_get_page,
	.invalidate_page = zcache_cleancache_flush_page,
	.invalidate_inode = zcache_cleancache_flush_inode,
	.invalidate_fs = zcache_cleancache_flush_fs,
	.init_shared_fs = zcache_cleancache_init_shared_fs,
	.init_fs = zcache_cleancache_init_fs
};

struct cleancache_ops zcache_cleancache_register_ops(void)
{
	struct cleancache_ops old_ops =
		cleancache_register_ops(&zcache_cleancache_ops);

	return old_ops;
}

/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
static int zcache_frontswap_poolid __read_mostly = -1;

/*
 * Swizzling increases objects per swaptype, increasing tmem concurrency
 * for heavy swaploads.  Later, larger nr_cpus -> larger SWIZ_BITS
 * Setting SWIZ_BITS to 27 basically reconstructs the swap entry from
 * frontswap_get_page(), but has side-effects. Hence using 8.
 */
#define SWIZ_BITS		8
#define SWIZ_MASK		((1 << SWIZ_BITS) - 1)
#define _oswiz(_type, _ind)	((_type << SWIZ_BITS) | (_ind & SWIZ_MASK))
#define iswiz(_ind)		(_ind >> SWIZ_BITS)

static inline struct tmem_oid oswiz(unsigned type, u32 ind)
{
	struct tmem_oid oid = { .oid = { 0 } };
	oid.oid[0] = _oswiz(type, ind);
	return oid;
}

#ifdef CONFIG_ZCACHE_WRITEBACK
static void unswiz(struct tmem_oid oid, u32 index,
				unsigned *type, pgoff_t *offset)
{
	*type = (unsigned)(oid.oid[0] >> SWIZ_BITS);
	*offset = (pgoff_t)((index << SWIZ_BITS) |
			(oid.oid[0] & SWIZ_MASK));
}
#endif

static int zcache_frontswap_put_page(unsigned type, pgoff_t offset,
					struct page *page)
{
	u64 ind64 = (u64)offset;
	u32 ind = (u32)offset;
	struct tmem_oid oid = oswiz(type, ind);
	int ret = -1;
	unsigned long flags;

	BUG_ON(!PageLocked(page));
	if (!disable_frontswap_ignore_nonactive && !PageWasActive(page)) {
		inc_zcache_pers_nonactive_puts_ignored();
		ret = -ERANGE;
		goto out;
	}
	if (likely(ind64 == ind)) {
		local_irq_save(flags);
		ret = zcache_put_page(LOCAL_CLIENT, zcache_frontswap_poolid,
					&oid, iswiz(ind),
					page, PAGE_SIZE, false, 0);
		local_irq_restore(flags);
	}
out:
	return ret;
}

/* returns 0 if the page was successfully gotten from frontswap, -1 if
 * was not present (should never happen!) */
static int zcache_frontswap_get_page(unsigned type, pgoff_t offset,
					struct page *page)
{
	u64 ind64 = (u64)offset;
	u32 ind = (u32)offset;
	struct tmem_oid oid = oswiz(type, ind);
	size_t size;
	int ret = -1, get_and_free;

	if (frontswap_has_exclusive_gets)
		get_and_free = 1;
	else
		get_and_free = -1;
	BUG_ON(!PageLocked(page));
	if (likely(ind64 == ind)) {
		ret = zcache_get_page(LOCAL_CLIENT, zcache_frontswap_poolid,
					&oid, iswiz(ind),
					page, &size, false, get_and_free);
		BUG_ON(ret >= 0 && size != PAGE_SIZE);
	}
	return ret;
}

/* flush a single page from frontswap */
static void zcache_frontswap_flush_page(unsigned type, pgoff_t offset)
{
	u64 ind64 = (u64)offset;
	u32 ind = (u32)offset;
	struct tmem_oid oid = oswiz(type, ind);

	if (likely(ind64 == ind))
		(void)zcache_flush_page(LOCAL_CLIENT, zcache_frontswap_poolid,
					&oid, iswiz(ind));
}

/* flush all pages from the passed swaptype */
static void zcache_frontswap_flush_area(unsigned type)
{
	struct tmem_oid oid;
	int ind;

	for (ind = SWIZ_MASK; ind >= 0; ind--) {
		oid = oswiz(type, ind);
		(void)zcache_flush_object(LOCAL_CLIENT,
						zcache_frontswap_poolid, &oid);
	}
}

static void zcache_frontswap_init(unsigned ignored)
{
	/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
	if (zcache_frontswap_poolid < 0)
		zcache_frontswap_poolid =
			zcache_local_new_pool(TMEM_POOL_PERSIST);
}

static struct frontswap_ops zcache_frontswap_ops = {
	.store = zcache_frontswap_put_page,
	.load = zcache_frontswap_get_page,
	.invalidate_page = zcache_frontswap_flush_page,
	.invalidate_area = zcache_frontswap_flush_area,
	.init = zcache_frontswap_init
};

struct frontswap_ops zcache_frontswap_register_ops(void)
{
	struct frontswap_ops old_ops =
		frontswap_register_ops(&zcache_frontswap_ops);

	return old_ops;
}

/*
 * zcache initialization
 * NOTE FOR NOW zcache or ramster MUST BE PROVIDED AS A KERNEL BOOT PARAMETER
 * OR NOTHING HAPPENS!
 */

static int __init enable_zcache(char *s)
{
	zcache_enabled = true;
	return 1;
}
__setup("zcache", enable_zcache);

static int __init enable_ramster(char *s)
{
	zcache_enabled = true;
#ifdef CONFIG_RAMSTER
	ramster_enabled = true;
#endif
	return 1;
}
__setup("ramster", enable_ramster);

/* allow independent dynamic disabling of cleancache and frontswap */

static int __init no_cleancache(char *s)
{
	disable_cleancache = true;
	return 1;
}

__setup("nocleancache", no_cleancache);

static int __init no_frontswap(char *s)
{
	disable_frontswap = true;
	return 1;
}

__setup("nofrontswap", no_frontswap);

static int __init no_frontswap_exclusive_gets(char *s)
{
	frontswap_has_exclusive_gets = false;
	return 1;
}

__setup("nofrontswapexclusivegets", no_frontswap_exclusive_gets);

static int __init no_frontswap_ignore_nonactive(char *s)
{
	disable_frontswap_ignore_nonactive = true;
	return 1;
}

__setup("nofrontswapignorenonactive", no_frontswap_ignore_nonactive);

static int __init no_cleancache_ignore_nonactive(char *s)
{
	disable_cleancache_ignore_nonactive = true;
	return 1;
}

__setup("nocleancacheignorenonactive", no_cleancache_ignore_nonactive);

static int __init enable_zcache_compressor(char *s)
{
	strlcpy(zcache_comp_name, s, sizeof(zcache_comp_name));
	zcache_enabled = true;
	return 1;
}
__setup("zcache=", enable_zcache_compressor);


static int __init zcache_comp_init(void)
{
	int ret = 0;

	/* check crypto algorithm */
	if (*zcache_comp_name != '\0') {
		ret = crypto_has_comp(zcache_comp_name, 0, 0);
		if (!ret)
			pr_info("zcache: %s not supported\n",
					zcache_comp_name);
	}
	if (!ret)
		strcpy(zcache_comp_name, "lzo");
	ret = crypto_has_comp(zcache_comp_name, 0, 0);
	if (!ret) {
		ret = 1;
		goto out;
	}
	pr_info("zcache: using %s compressor\n", zcache_comp_name);

	/* alloc percpu transforms */
	ret = 0;
	zcache_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
	if (!zcache_comp_pcpu_tfms)
		ret = 1;
out:
	return ret;
}

static int __init zcache_init(void)
{
	int ret = 0;

	if (ramster_enabled) {
		namestr = "ramster";
		ramster_register_pamops(&zcache_pamops);
	}
#ifdef CONFIG_DEBUG_FS
	zcache_debugfs_init();
#endif
	if (zcache_enabled) {
		unsigned int cpu;

		tmem_register_hostops(&zcache_hostops);
		tmem_register_pamops(&zcache_pamops);
		ret = register_cpu_notifier(&zcache_cpu_notifier_block);
		if (ret) {
			pr_err("%s: can't register cpu notifier\n", namestr);
			goto out;
		}
		ret = zcache_comp_init();
		if (ret) {
			pr_err("%s: compressor initialization failed\n",
				namestr);
			goto out;
		}
		for_each_online_cpu(cpu) {
			void *pcpu = (void *)(long)cpu;
			zcache_cpu_notifier(&zcache_cpu_notifier_block,
				CPU_UP_PREPARE, pcpu);
		}
	}
	zcache_objnode_cache = kmem_cache_create("zcache_objnode",
				sizeof(struct tmem_objnode), 0, 0, NULL);
	zcache_obj_cache = kmem_cache_create("zcache_obj",
				sizeof(struct tmem_obj), 0, 0, NULL);
	ret = zcache_new_client(LOCAL_CLIENT);
	if (ret) {
		pr_err("%s: can't create client\n", namestr);
		goto out;
	}
	zbud_init();
	if (zcache_enabled && !disable_cleancache) {
		struct cleancache_ops old_ops;

		register_shrinker(&zcache_shrinker);
		old_ops = zcache_cleancache_register_ops();
		pr_info("%s: cleancache enabled using kernel transcendent "
			"memory and compression buddies\n", namestr);
#ifdef CONFIG_ZCACHE_DEBUG
		pr_info("%s: cleancache: ignorenonactive = %d\n",
			namestr, !disable_cleancache_ignore_nonactive);
#endif
		if (old_ops.init_fs != NULL)
			pr_warn("%s: cleancache_ops overridden\n", namestr);
	}
	if (zcache_enabled && !disable_frontswap) {
		struct frontswap_ops old_ops;

		old_ops = zcache_frontswap_register_ops();
		if (frontswap_has_exclusive_gets)
			frontswap_tmem_exclusive_gets(true);
		pr_info("%s: frontswap enabled using kernel transcendent "
			"memory and compression buddies\n", namestr);
#ifdef CONFIG_ZCACHE_DEBUG
		pr_info("%s: frontswap: excl gets = %d active only = %d\n",
			namestr, frontswap_has_exclusive_gets,
			!disable_frontswap_ignore_nonactive);
#endif
		if (old_ops.init != NULL)
			pr_warn("%s: frontswap_ops overridden\n", namestr);
	}
	if (ramster_enabled)
		ramster_init(!disable_cleancache, !disable_frontswap,
				frontswap_has_exclusive_gets);
out:
	return ret;
}

late_initcall(zcache_init);