[deliverable/linux.git] / drivers / staging / zcache / ramster / ramster.c

/*
 * ramster.c
 *
 * Copyright (c) 2010-2012, Dan Magenheimer, Oracle Corp.
 *
 * RAMster implements peer-to-peer transcendent memory, allowing a "cluster" of
 * kernels to dynamically pool their RAM so that a RAM-hungry workload on one
 * machine can temporarily and transparently utilize RAM on another machine
 * which is presumably idle or running a non-RAM-hungry workload.
 *
 * RAMster combines a clustering and messaging foundation based on the ocfs2
 * cluster layer with the in-kernel compression implementation of zcache, and
 * adds code to glue them together.  When a page is "put" to RAMster, it is
 * compressed and stored locally.  Periodically, a thread will "remotify" these
 * pages by sending them via messages to a remote machine.  When the page is
 * later needed as indicated by a page fault, a "get" is issued.  If the data
 * is local, it is uncompressed and the fault is resolved.  If the data is
 * remote, a message is sent to fetch the data and the faulting thread sleeps;
 * when the data arrives, the thread awakens, the data is decompressed and
 * the fault is resolved.

 * As of V5, clusters up to eight nodes are supported; each node can remotify
 * pages to one specified node, so clusters can be configured as clients to
 * a "memory server".  Some simple policy is in place that will need to be
 * refined over time.  Larger clusters and fault-resistant protocols can also
 * be added over time.
 */

#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/list.h>
#include <linux/lzo.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/frontswap.h>
#include "../tmem.h"
#include "../zcache.h"
#include "../zbud.h"
#include "ramster.h"
#include "ramster_nodemanager.h"
#include "tcp.h"
#include "debug.h"

#define RAMSTER_TESTING

#ifndef CONFIG_SYSFS
#error "ramster needs sysfs to define cluster nodes to use"
#endif

static bool use_cleancache __read_mostly;
static bool use_frontswap __read_mostly;
static bool use_frontswap_exclusive_gets __read_mostly;

/* These must be sysfs not debugfs as they are checked/used by userland!! */
static unsigned long ramster_interface_revision __read_mostly =
        R2NM_API_VERSION; /* interface revision must match userspace! */
static unsigned long ramster_pers_remotify_enable __read_mostly;
static unsigned long ramster_eph_remotify_enable __read_mostly;
static atomic_t ramster_remote_pers_pages = ATOMIC_INIT(0);
#define MANUAL_NODES 8
static bool ramster_nodes_manual_up[MANUAL_NODES] __read_mostly;
static int ramster_remote_target_nodenum __read_mostly = -1;

/* Used by this code. */
long ramster_flnodes;
ssize_t ramster_foreign_eph_pages;
ssize_t ramster_foreign_pers_pages;
/* FIXME frontswap selfshrinking knobs in debugfs? */

static LIST_HEAD(ramster_rem_op_list);
static DEFINE_SPINLOCK(ramster_rem_op_list_lock);
static DEFINE_PER_CPU(struct ramster_preload, ramster_preloads);

static DEFINE_PER_CPU(unsigned char *, ramster_remoteputmem1);
static DEFINE_PER_CPU(unsigned char *, ramster_remoteputmem2);

static struct kmem_cache *ramster_flnode_cache __read_mostly;

static struct flushlist_node *ramster_flnode_alloc(struct tmem_pool *pool)
{
        struct flushlist_node *flnode = NULL;
        struct ramster_preload *kp;

        kp = &__get_cpu_var(ramster_preloads);
        flnode = kp->flnode;
        BUG_ON(flnode == NULL);
        kp->flnode = NULL;
        inc_ramster_flnodes();
        return flnode;
}

/* the "flush list" asynchronously collects pages to remotely flush */
#define FLUSH_ENTIRE_OBJECT ((uint32_t)-1)
static void ramster_flnode_free(struct flushlist_node *flnode,
                                struct tmem_pool *pool)
{
        dec_ramster_flnodes();
        BUG_ON(ramster_flnodes < 0);
        kmem_cache_free(ramster_flnode_cache, flnode);
}

int ramster_do_preload_flnode(struct tmem_pool *pool)
{
        struct ramster_preload *kp;
        struct flushlist_node *flnode;
        int ret = -ENOMEM;

        BUG_ON(!irqs_disabled());
        if (unlikely(ramster_flnode_cache == NULL))
                BUG();
        kp = &__get_cpu_var(ramster_preloads);
        flnode = kmem_cache_alloc(ramster_flnode_cache, GFP_ATOMIC);
        if (unlikely(flnode == NULL) && kp->flnode == NULL)
                BUG();  /* FIXME handle more gracefully, but how??? */
        else if (kp->flnode == NULL)
                kp->flnode = flnode;
        else
                kmem_cache_free(ramster_flnode_cache, flnode);
        return ret;
}
EXPORT_SYMBOL_GPL(ramster_do_preload_flnode);

/*
 * Called by the message handler after a (still compressed) page has been
 * fetched from the remote machine in response to an "is_remote" tmem_get
 * or persistent tmem_localify.  For a tmem_get, "extra" is the address of
 * the page that is to be filled to successfully resolve the tmem_get; for
 * a (persistent) tmem_localify, "extra" is NULL (as the data is placed only
 * in the local zcache).  "data" points to "size" bytes of (compressed) data
 * passed in the message.  In the case of a persistent remote get, if
 * pre-allocation was successful (see ramster_repatriate_preload), the page
 * is placed into both local zcache and at "extra".
 */
int ramster_localify(int pool_id, struct tmem_oid *oidp, uint32_t index,
                        char *data, unsigned int size, void *extra)
{
        int ret = -ENOENT;
        unsigned long flags;
        struct tmem_pool *pool;
        bool eph, delete = false;
        void *pampd, *saved_hb;
        struct tmem_obj *obj;

        pool = zcache_get_pool_by_id(LOCAL_CLIENT, pool_id);
        if (unlikely(pool == NULL))
                /* pool doesn't exist anymore */
                goto out;
        eph = is_ephemeral(pool);
        local_irq_save(flags);  /* FIXME: maybe only disable softirqs? */
        pampd = tmem_localify_get_pampd(pool, oidp, index, &obj, &saved_hb);
        if (pampd == NULL) {
                /* hmmm... must have been a flush while waiting */
#ifdef RAMSTER_TESTING
                pr_err("UNTESTED pampd==NULL in ramster_localify\n");
#endif
                if (eph)
                        inc_ramster_remote_eph_pages_unsucc_get();
                else
                        inc_ramster_remote_pers_pages_unsucc_get();
                obj = NULL;
                goto finish;
        } else if (unlikely(!pampd_is_remote(pampd))) {
                /* hmmm... must have been a dup put while waiting */
#ifdef RAMSTER_TESTING
                pr_err("UNTESTED dup while waiting in ramster_localify\n");
#endif
                if (eph)
                        inc_ramster_remote_eph_pages_unsucc_get();
                else
                        inc_ramster_remote_pers_pages_unsucc_get();
                obj = NULL;
                pampd = NULL;
                ret = -EEXIST;
                goto finish;
        } else if (size == 0) {
                /* no remote data, delete the local is_remote pampd */
                pampd = NULL;
                if (eph)
                        inc_ramster_remote_eph_pages_unsucc_get();
                else
                        BUG();
                delete = true;
                goto finish;
        }
        if (pampd_is_intransit(pampd)) {
                /*
                 *  a pampd is marked intransit if it is remote and space has
                 *  been allocated for it locally (note, only happens for
                 *  persistent pages, in which case the remote copy is freed)
                 */
                BUG_ON(eph);
                pampd = pampd_mask_intransit_and_remote(pampd);
                zbud_copy_to_zbud(pampd, data, size);
        } else {
                /*
                 * setting pampd to NULL tells tmem_localify_finish to leave
                 * pampd alone... meaning it is left pointing to the
                 * remote copy
                 */
                pampd = NULL;
                obj = NULL;
        }
        /*
         * but in all cases, we decompress direct-to-memory to complete
         * the remotify and return success
         */
        BUG_ON(extra == NULL);
        zcache_decompress_to_page(data, size, (struct page *)extra);
        if (eph)
                inc_ramster_remote_eph_pages_succ_get();
        else
                inc_ramster_remote_pers_pages_succ_get();
        ret = 0;
finish:
        tmem_localify_finish(obj, index, pampd, saved_hb, delete);
        zcache_put_pool(pool);
        local_irq_restore(flags);
out:
        return ret;
}

void ramster_pampd_new_obj(struct tmem_obj *obj)
{
        obj->extra = NULL;
}

void ramster_pampd_free_obj(struct tmem_pool *pool, struct tmem_obj *obj,
                                bool pool_destroy)
{
        struct flushlist_node *flnode;

        BUG_ON(preemptible());
        if (obj->extra == NULL)
                return;
        if (pool_destroy && is_ephemeral(pool))
                /* FIXME don't bother with remote eph data for now */
                return;
        BUG_ON(!pampd_is_remote(obj->extra));
        flnode = ramster_flnode_alloc(pool);
        flnode->xh.client_id = pampd_remote_node(obj->extra);
        flnode->xh.pool_id = pool->pool_id;
        flnode->xh.oid = obj->oid;
        flnode->xh.index = FLUSH_ENTIRE_OBJECT;
        flnode->rem_op.op = RAMSTER_REMOTIFY_FLUSH_OBJ;
        spin_lock(&ramster_rem_op_list_lock);
        list_add(&flnode->rem_op.list, &ramster_rem_op_list);
        spin_unlock(&ramster_rem_op_list_lock);
}

/*
 * Called on a remote persistent tmem_get to attempt to preallocate
 * local storage for the data contained in the remote persistent page.
 * If successfully preallocated, returns the pampd, marked as remote and
 * in_transit.  Else returns NULL.  Note that the appropriate tmem data
 * structure must be locked.
 */
void *ramster_pampd_repatriate_preload(void *pampd, struct tmem_pool *pool,
                                        struct tmem_oid *oidp, uint32_t index,
                                        bool *intransit)
{
        int clen = pampd_remote_size(pampd), c;
        void *ret_pampd = NULL;
        unsigned long flags;
        struct tmem_handle th;

        BUG_ON(!pampd_is_remote(pampd));
        BUG_ON(is_ephemeral(pool));
        if (use_frontswap_exclusive_gets)
                /* don't need local storage */
                goto out;
        if (pampd_is_intransit(pampd)) {
                /*
                 * to avoid multiple allocations (and maybe a memory leak)
                 * don't preallocate if already in the process of being
                 * repatriated
                 */
                *intransit = true;
                goto out;
        }
        *intransit = false;
        local_irq_save(flags);
        th.client_id = pampd_remote_node(pampd);
        th.pool_id = pool->pool_id;
        th.oid = *oidp;
        th.index = index;
        ret_pampd = zcache_pampd_create(NULL, clen, true, false, &th);
        if (ret_pampd != NULL) {
                /*
                 *  a pampd is marked intransit if it is remote and space has
                 *  been allocated for it locally (note, only happens for
                 *  persistent pages, in which case the remote copy is freed)
                 */
                ret_pampd = pampd_mark_intransit(ret_pampd);
                c = atomic_dec_return(&ramster_remote_pers_pages);
                WARN_ON_ONCE(c < 0);
        } else {
                inc_ramster_pers_pages_remote_nomem();
        }
        local_irq_restore(flags);
out:
        return ret_pampd;
}

/*
 * Called on a remote tmem_get to invoke a message to fetch the page.
 * Might sleep so no tmem locks can be held.  "extra" is passed
 * all the way through the round-trip messaging to ramster_localify.
 */
int ramster_pampd_repatriate(void *fake_pampd, void *real_pampd,
                                struct tmem_pool *pool,
                                struct tmem_oid *oid, uint32_t index,
                                bool free, void *extra)
{
        struct tmem_xhandle xh;
        int ret;

        if (pampd_is_intransit(real_pampd))
                /* have local space pre-reserved, so free remote copy */
                free = true;
        xh = tmem_xhandle_fill(LOCAL_CLIENT, pool, oid, index);
        /* unreliable request/response for now */
        ret = r2net_remote_async_get(&xh, free,
                                        pampd_remote_node(fake_pampd),
                                        pampd_remote_size(fake_pampd),
                                        pampd_remote_cksum(fake_pampd),
                                        extra);
        return ret;
}

bool ramster_pampd_is_remote(void *pampd)
{
        return pampd_is_remote(pampd);
}

int ramster_pampd_replace_in_obj(void *new_pampd, struct tmem_obj *obj)
{
        int ret = -1;

        if (new_pampd != NULL) {
                if (obj->extra == NULL)
                        obj->extra = new_pampd;
                /* enforce that all remote pages in an object reside
                 * in the same node! */
                else if (pampd_remote_node(new_pampd) !=
                                pampd_remote_node((void *)(obj->extra)))
                        BUG();
                ret = 0;
        }
        return ret;
}

void *ramster_pampd_free(void *pampd, struct tmem_pool *pool,
                              struct tmem_oid *oid, uint32_t index, bool acct)
{
        bool eph = is_ephemeral(pool);
        void *local_pampd = NULL;
        int c;

        BUG_ON(preemptible());
        BUG_ON(!pampd_is_remote(pampd));
        WARN_ON(acct == false);
        if (oid == NULL) {
                /*
                 * a NULL oid means to ignore this pampd free
                 * as the remote freeing will be handled elsewhere
                 */
        } else if (eph) {
                /* FIXME remote flush optional but probably good idea */
        } else if (pampd_is_intransit(pampd)) {
                /* did a pers remote get_and_free, so just free local */
                local_pampd = pampd_mask_intransit_and_remote(pampd);
        } else {
                struct flushlist_node *flnode =
                        ramster_flnode_alloc(pool);

                flnode->xh.client_id = pampd_remote_node(pampd);
                flnode->xh.pool_id = pool->pool_id;
                flnode->xh.oid = *oid;
                flnode->xh.index = index;
                flnode->rem_op.op = RAMSTER_REMOTIFY_FLUSH_PAGE;
                spin_lock(&ramster_rem_op_list_lock);
                list_add(&flnode->rem_op.list, &ramster_rem_op_list);
                spin_unlock(&ramster_rem_op_list_lock);
                c = atomic_dec_return(&ramster_remote_pers_pages);
                WARN_ON_ONCE(c < 0);
        }
        return local_pampd;
}
EXPORT_SYMBOL_GPL(ramster_pampd_free);

void ramster_count_foreign_pages(bool eph, int count)
{
        BUG_ON(count != 1 && count != -1);
        if (eph) {
                if (count > 0) {
                        inc_ramster_foreign_eph_pages();
                } else {
                        dec_ramster_foreign_eph_pages();
                        WARN_ON_ONCE(ramster_foreign_eph_pages < 0);
                }
        } else {
                if (count > 0) {
                        inc_ramster_foreign_pers_pages();
                } else {
                        dec_ramster_foreign_pers_pages();
                        WARN_ON_ONCE(ramster_foreign_pers_pages < 0);
                }
        }
}
EXPORT_SYMBOL_GPL(ramster_count_foreign_pages);

/*
 * For now, just push over a few pages every few seconds to
 * ensure that it basically works
 */
static struct workqueue_struct *ramster_remotify_workqueue;
static void ramster_remotify_process(struct work_struct *work);
static DECLARE_DELAYED_WORK(ramster_remotify_worker,
                ramster_remotify_process);

static void ramster_remotify_queue_delayed_work(unsigned long delay)
{
        if (!queue_delayed_work(ramster_remotify_workqueue,
                                &ramster_remotify_worker, delay))
                pr_err("ramster_remotify: bad workqueue\n");
}

static void ramster_remote_flush_page(struct flushlist_node *flnode)
{
        struct tmem_xhandle *xh;
        int remotenode, ret;

        preempt_disable();
        xh = &flnode->xh;
        remotenode = flnode->xh.client_id;
        ret = r2net_remote_flush(xh, remotenode);
        if (ret >= 0)
                inc_ramster_remote_pages_flushed();
        else
                inc_ramster_remote_page_flushes_failed();
        preempt_enable_no_resched();
        ramster_flnode_free(flnode, NULL);
}

static void ramster_remote_flush_object(struct flushlist_node *flnode)
{
        struct tmem_xhandle *xh;
        int remotenode, ret;

        preempt_disable();
        xh = &flnode->xh;
        remotenode = flnode->xh.client_id;
        ret = r2net_remote_flush_object(xh, remotenode);
        if (ret >= 0)
                inc_ramster_remote_objects_flushed();
        else
                inc_ramster_remote_object_flushes_failed();
        preempt_enable_no_resched();
        ramster_flnode_free(flnode, NULL);
}

int ramster_remotify_pageframe(bool eph)
{
        struct tmem_xhandle xh;
        unsigned int size;
        int remotenode, ret, zbuds;
        struct tmem_pool *pool;
        unsigned long flags;
        unsigned char cksum;
        char *p;
        int i, j;
        unsigned char *tmpmem[2];
        struct tmem_handle th[2];
        unsigned int zsize[2];

        tmpmem[0] = __get_cpu_var(ramster_remoteputmem1);
        tmpmem[1] = __get_cpu_var(ramster_remoteputmem2);
        local_bh_disable();
        zbuds = zbud_make_zombie_lru(&th[0], &tmpmem[0], &zsize[0], eph);
        /* now OK to release lock set in caller */
        local_bh_enable();
        if (zbuds == 0)
                goto out;
        BUG_ON(zbuds > 2);
        for (i = 0; i < zbuds; i++) {
                xh.client_id = th[i].client_id;
                xh.pool_id = th[i].pool_id;
                xh.oid = th[i].oid;
                xh.index = th[i].index;
                size = zsize[i];
                BUG_ON(size == 0 || size > zbud_max_buddy_size());
                for (p = tmpmem[i], cksum = 0, j = 0; j < size; j++)
                        cksum += *p++;
                ret = r2net_remote_put(&xh, tmpmem[i], size, eph, &remotenode);
                if (ret != 0) {
                /*
                 * This is some form of a memory leak... if the remote put
                 * fails, there will never be another attempt to remotify
                 * this page.  But since we've dropped the zv pointer,
                 * the page may have been freed or the data replaced
                 * so we can't just "put it back" in the remote op list.
                 * Even if we could, not sure where to put it in the list
                 * because there may be flushes that must be strictly
                 * ordered vs the put.  So leave this as a FIXME for now.
                 * But count them so we know if it becomes a problem.
                 */
                        if (eph)
                                inc_ramster_eph_pages_remote_failed();
                        else
                                inc_ramster_pers_pages_remote_failed();
                        break;
                } else {
                        if (!eph)
                                atomic_inc(&ramster_remote_pers_pages);
                }
                if (eph)
                        inc_ramster_eph_pages_remoted();
                else
                        inc_ramster_pers_pages_remoted();
                /*
                 * data was successfully remoted so change the local version to
                 * point to the remote node where it landed
                 */
                local_bh_disable();
                pool = zcache_get_pool_by_id(LOCAL_CLIENT, xh.pool_id);
                local_irq_save(flags);
                (void)tmem_replace(pool, &xh.oid, xh.index,
                                pampd_make_remote(remotenode, size, cksum));
                local_irq_restore(flags);
                zcache_put_pool(pool);
                local_bh_enable();
        }
out:
        return zbuds;
}

static void zcache_do_remotify_flushes(void)
{
        struct ramster_remotify_hdr *rem_op;
        union remotify_list_node *u;

        while (1) {
                spin_lock(&ramster_rem_op_list_lock);
                if (list_empty(&ramster_rem_op_list)) {
                        spin_unlock(&ramster_rem_op_list_lock);
                        goto out;
                }
                rem_op = list_first_entry(&ramster_rem_op_list,
                                struct ramster_remotify_hdr, list);
                list_del_init(&rem_op->list);
                spin_unlock(&ramster_rem_op_list_lock);
                u = (union remotify_list_node *)rem_op;
                switch (rem_op->op) {
                case RAMSTER_REMOTIFY_FLUSH_PAGE:
                        ramster_remote_flush_page((struct flushlist_node *)u);
                        break;
                case RAMSTER_REMOTIFY_FLUSH_OBJ:
                        ramster_remote_flush_object((struct flushlist_node *)u);
                        break;
                default:
                        BUG();
                }
        }
out:
        return;
}

static void ramster_remotify_process(struct work_struct *work)
{
        static bool remotify_in_progress;
        int i;

        BUG_ON(irqs_disabled());
        if (remotify_in_progress)
                goto requeue;
        if (ramster_remote_target_nodenum == -1)
                goto requeue;
        remotify_in_progress = true;
        if (use_cleancache && ramster_eph_remotify_enable) {
                for (i = 0; i < 100; i++) {
                        zcache_do_remotify_flushes();
                        (void)ramster_remotify_pageframe(true);
                }
        }
        if (use_frontswap && ramster_pers_remotify_enable) {
                for (i = 0; i < 100; i++) {
                        zcache_do_remotify_flushes();
                        (void)ramster_remotify_pageframe(false);
                }
        }
        remotify_in_progress = false;
requeue:
        ramster_remotify_queue_delayed_work(HZ);
}

void ramster_remotify_init(void)
{
        unsigned long n = 60UL;
        ramster_remotify_workqueue =
                create_singlethread_workqueue("ramster_remotify");
        ramster_remotify_queue_delayed_work(n * HZ);
}

static ssize_t ramster_manual_node_up_show(struct kobject *kobj,
                                struct kobj_attribute *attr, char *buf)
{
        int i;
        char *p = buf;
        for (i = 0; i < MANUAL_NODES; i++)
                if (ramster_nodes_manual_up[i])
                        p += sprintf(p, "%d ", i);
        p += sprintf(p, "\n");
        return p - buf;
}

static ssize_t ramster_manual_node_up_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        int err;
        unsigned long node_num;

        err = kstrtoul(buf, 10, &node_num);
        if (err) {
                pr_err("ramster: bad strtoul?\n");
                return -EINVAL;
        }
        if (node_num >= MANUAL_NODES) {
                pr_err("ramster: bad node_num=%lu?\n", node_num);
                return -EINVAL;
        }
        if (ramster_nodes_manual_up[node_num]) {
                pr_err("ramster: node %d already up, ignoring\n",
                                                        (int)node_num);
        } else {
                ramster_nodes_manual_up[node_num] = true;
                r2net_hb_node_up_manual((int)node_num);
        }
        return count;
}

static struct kobj_attribute ramster_manual_node_up_attr = {
        .attr = { .name = "manual_node_up", .mode = 0644 },
        .show = ramster_manual_node_up_show,
        .store = ramster_manual_node_up_store,
};

static ssize_t ramster_remote_target_nodenum_show(struct kobject *kobj,
                                struct kobj_attribute *attr, char *buf)
{
        if (ramster_remote_target_nodenum == -1UL)
                return sprintf(buf, "unset\n");
        else
                return sprintf(buf, "%d\n", ramster_remote_target_nodenum);
}

static ssize_t ramster_remote_target_nodenum_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        int err;
        unsigned long node_num;

        err = kstrtoul(buf, 10, &node_num);
        if (err) {
                pr_err("ramster: bad strtoul?\n");
                return -EINVAL;
        } else if (node_num == -1UL) {
                pr_err("ramster: disabling all remotification, "
                        "data may still reside on remote nodes however\n");
                return -EINVAL;
        } else if (node_num >= MANUAL_NODES) {
                pr_err("ramster: bad node_num=%lu?\n", node_num);
                return -EINVAL;
        } else if (!ramster_nodes_manual_up[node_num]) {
                pr_err("ramster: node %d not up, ignoring setting "
                        "of remotification target\n", (int)node_num);
        } else if (r2net_remote_target_node_set((int)node_num) >= 0) {
                pr_info("ramster: node %d set as remotification target\n",
                                (int)node_num);
                ramster_remote_target_nodenum = (int)node_num;
        } else {
                pr_err("ramster: bad num to node node_num=%d?\n",
                                (int)node_num);
                return -EINVAL;
        }
        return count;
}

static struct kobj_attribute ramster_remote_target_nodenum_attr = {
        .attr = { .name = "remote_target_nodenum", .mode = 0644 },
        .show = ramster_remote_target_nodenum_show,
        .store = ramster_remote_target_nodenum_store,
};

#define RAMSTER_SYSFS_RO(_name) \
        static ssize_t ramster_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
                return sprintf(buf, "%lu\n", ramster_##_name); \
        } \
        static struct kobj_attribute ramster_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0444 }, \
                .show = ramster_##_name##_show, \
        }

#define RAMSTER_SYSFS_RW(_name) \
        static ssize_t ramster_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
                return sprintf(buf, "%lu\n", ramster_##_name); \
        } \
        static ssize_t ramster_##_name##_store(struct kobject *kobj, \
                struct kobj_attribute *attr, const char *buf, size_t count) \
        { \
                int err; \
                unsigned long enable; \
                err = kstrtoul(buf, 10, &enable); \
                if (err) \
                        return -EINVAL; \
                ramster_##_name = enable; \
                return count; \
        } \
        static struct kobj_attribute ramster_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0644 }, \
                .show = ramster_##_name##_show, \
                .store = ramster_##_name##_store, \
        }

#define RAMSTER_SYSFS_RO_ATOMIC(_name) \
        static ssize_t ramster_##_name##_show(struct kobject *kobj, \
                                struct kobj_attribute *attr, char *buf) \
        { \
            return sprintf(buf, "%d\n", atomic_read(&ramster_##_name)); \
        } \
        static struct kobj_attribute ramster_##_name##_attr = { \
                .attr = { .name = __stringify(_name), .mode = 0444 }, \
                .show = ramster_##_name##_show, \
        }

RAMSTER_SYSFS_RO(interface_revision);
RAMSTER_SYSFS_RO_ATOMIC(remote_pers_pages);
RAMSTER_SYSFS_RW(pers_remotify_enable);
RAMSTER_SYSFS_RW(eph_remotify_enable);

static struct attribute *ramster_attrs[] = {
        &ramster_interface_revision_attr.attr,
        &ramster_remote_pers_pages_attr.attr,
        &ramster_manual_node_up_attr.attr,
        &ramster_remote_target_nodenum_attr.attr,
        &ramster_pers_remotify_enable_attr.attr,
        &ramster_eph_remotify_enable_attr.attr,
        NULL,
};

static struct attribute_group ramster_attr_group = {
        .attrs = ramster_attrs,
        .name = "ramster",
};

/*
 * frontswap selfshrinking
 */

/* In HZ, controls frequency of worker invocation. */
static unsigned int selfshrink_interval __read_mostly = 5;
/* Enable/disable with sysfs. */
static bool frontswap_selfshrinking __read_mostly;

static void selfshrink_process(struct work_struct *work);
static DECLARE_DELAYED_WORK(selfshrink_worker, selfshrink_process);

#ifndef CONFIG_RAMSTER_MODULE
/* Enable/disable with kernel boot option. */
static bool use_frontswap_selfshrink = true;
#endif

/*
 * The default values for the following parameters were deemed reasonable
 * by experimentation, may be workload-dependent, and can all be
 * adjusted via sysfs.
 */

/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
static unsigned int frontswap_hysteresis __read_mostly = 20;

/*
 * Number of selfshrink worker invocations to wait before observing that
 * frontswap selfshrinking should commence. Note that selfshrinking does
 * not use a separate worker thread.
 */
static unsigned int frontswap_inertia __read_mostly = 3;

/* Countdown to next invocation of frontswap_shrink() */
static unsigned long frontswap_inertia_counter;

/*
 * Invoked by the selfshrink worker thread, uses current number of pages
 * in frontswap (frontswap_curr_pages()), previous status, and control
 * values (hysteresis and inertia) to determine if frontswap should be
 * shrunk and what the new frontswap size should be.  Note that
 * frontswap_shrink is essentially a partial swapoff that immediately
 * transfers pages from the "swap device" (frontswap) back into kernel
 * RAM; despite the name, frontswap "shrinking" is very different from
 * the "shrinker" interface used by the kernel MM subsystem to reclaim
 * memory.
 */
static void frontswap_selfshrink(void)
{
        static unsigned long cur_frontswap_pages;
        static unsigned long last_frontswap_pages;
        static unsigned long tgt_frontswap_pages;

        last_frontswap_pages = cur_frontswap_pages;
        cur_frontswap_pages = frontswap_curr_pages();
        if (!cur_frontswap_pages ||
                        (cur_frontswap_pages > last_frontswap_pages)) {
                frontswap_inertia_counter = frontswap_inertia;
                return;
        }
        if (frontswap_inertia_counter && --frontswap_inertia_counter)
                return;
        if (cur_frontswap_pages <= frontswap_hysteresis)
                tgt_frontswap_pages = 0;
        else
                tgt_frontswap_pages = cur_frontswap_pages -
                        (cur_frontswap_pages / frontswap_hysteresis);
        frontswap_shrink(tgt_frontswap_pages);
}

#ifndef CONFIG_RAMSTER_MODULE
static int __init ramster_nofrontswap_selfshrink_setup(char *s)
{
        use_frontswap_selfshrink = false;
        return 1;
}

__setup("noselfshrink", ramster_nofrontswap_selfshrink_setup);
#endif

static void selfshrink_process(struct work_struct *work)
{
        if (frontswap_selfshrinking && frontswap_enabled) {
                frontswap_selfshrink();
                schedule_delayed_work(&selfshrink_worker,
                        selfshrink_interval * HZ);
        }
}

void ramster_cpu_up(int cpu)
{
        unsigned char *p1 = kzalloc(PAGE_SIZE, GFP_KERNEL | __GFP_REPEAT);
        unsigned char *p2 = kzalloc(PAGE_SIZE, GFP_KERNEL | __GFP_REPEAT);
        BUG_ON(!p1 || !p2);
        per_cpu(ramster_remoteputmem1, cpu) = p1;
        per_cpu(ramster_remoteputmem2, cpu) = p2;
}
EXPORT_SYMBOL_GPL(ramster_cpu_up);

void ramster_cpu_down(int cpu)
{
        struct ramster_preload *kp;

        kfree(per_cpu(ramster_remoteputmem1, cpu));
        per_cpu(ramster_remoteputmem1, cpu) = NULL;
        kfree(per_cpu(ramster_remoteputmem2, cpu));
        per_cpu(ramster_remoteputmem2, cpu) = NULL;
        kp = &per_cpu(ramster_preloads, cpu);
        if (kp->flnode) {
                kmem_cache_free(ramster_flnode_cache, kp->flnode);
                kp->flnode = NULL;
        }
}
EXPORT_SYMBOL_GPL(ramster_cpu_down);

void ramster_register_pamops(struct tmem_pamops *pamops)
{
        pamops->free_obj = ramster_pampd_free_obj;
        pamops->new_obj = ramster_pampd_new_obj;
        pamops->replace_in_obj = ramster_pampd_replace_in_obj;
        pamops->is_remote = ramster_pampd_is_remote;
        pamops->repatriate = ramster_pampd_repatriate;
        pamops->repatriate_preload = ramster_pampd_repatriate_preload;
}
EXPORT_SYMBOL_GPL(ramster_register_pamops);

void ramster_init(bool cleancache, bool frontswap,
                                bool frontswap_exclusive_gets,
                                bool frontswap_selfshrink)
{
        int ret = 0;

        if (cleancache)
                use_cleancache = true;
        if (frontswap)
                use_frontswap = true;
        if (frontswap_exclusive_gets)
                use_frontswap_exclusive_gets = true;
        ramster_debugfs_init();
        ret = sysfs_create_group(mm_kobj, &ramster_attr_group);
        if (ret)
                pr_err("ramster: can't create sysfs for ramster\n");
        (void)r2net_register_handlers();
#ifdef CONFIG_RAMSTER_MODULE
        ret = r2nm_init();
        if (ret)
                pr_err("ramster: can't init r2net\n");
        frontswap_selfshrinking = frontswap_selfshrink;
#else
        frontswap_selfshrinking = use_frontswap_selfshrink;
#endif
        INIT_LIST_HEAD(&ramster_rem_op_list);
        ramster_flnode_cache = kmem_cache_create("ramster_flnode",
                                sizeof(struct flushlist_node), 0, 0, NULL);
        if (frontswap_selfshrinking) {
                pr_info("ramster: Initializing frontswap selfshrink driver.\n");
                schedule_delayed_work(&selfshrink_worker,
                                        selfshrink_interval * HZ);
        }
        ramster_remotify_init();
}
EXPORT_SYMBOL_GPL(ramster_init);