memory_hotplug.c

Go to the documentation of this file.

/*
 *  linux/mm/memory_hotplug.c
 *
 *  Copyright (C)
 */

#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
#include <linux/pagemap.h>
#include <linux/bootmem.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/memory.h>
#include <linux/memory_hotplug.h>
#include <linux/highmem.h>
#include <linux/vmalloc.h>
#include <linux/ioport.h>
#include <linux/delay.h>
#include <linux/migrate.h>
#include <linux/page-isolation.h>
#include <linux/pfn.h>
#include <linux/suspend.h>
#include <linux/mm_inline.h>
#include <linux/firmware-map.h>

#include <asm/tlbflush.h>

#include "internal.h"

/*
 * online_page_callback contains pointer to current page onlining function.
 * Initially it is generic_online_page(). If it is required it could be
 * changed by calling set_online_page_callback() for callback registration
 * and restore_online_page_callback() for generic callback restore.
 */

static void generic_online_page(struct page *page);

static online_page_callback_t online_page_callback = generic_online_page;

DEFINE_MUTEX(mem_hotplug_mutex);

void lock_memory_hotplug(void)
{
    mutex_lock(&mem_hotplug_mutex);

    /* for exclusive hibernation if CONFIG_HIBERNATION=y */
    lock_system_sleep();
}

void unlock_memory_hotplug(void)
{
    unlock_system_sleep();
    mutex_unlock(&mem_hotplug_mutex);
}


/* add this memory to iomem resource */
static struct resource *register_memory_resource(u64 start, u64 size)
{
    struct resource *res;
    res = kzalloc(sizeof(struct resource), GFP_KERNEL);
    BUG_ON(!res);

    res->name = "System RAM";
    res->start = start;
    res->end = start + size - 1;
    res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
    if (request_resource(&iomem_resource, res) < 0) {
        printk("System RAM resource %pR cannot be added\n", res);
        kfree(res);
        res = NULL;
    }
    return res;
}

static void release_memory_resource(struct resource *res)
{
    if (!res)
        return;
    release_resource(res);
    kfree(res);
    return;
}

#ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
#ifndef CONFIG_SPARSEMEM_VMEMMAP
static void get_page_bootmem(unsigned long info,  struct page *page,
                 unsigned long type)
{
    page->lru.next = (struct list_head *) type;
    SetPagePrivate(page);
    set_page_private(page, info);
    atomic_inc(&page->_count);
}

/* reference to __meminit __free_pages_bootmem is valid
 * so use __ref to tell modpost not to generate a warning */
void __ref put_page_bootmem(struct page *page)
{
    unsigned long type;

    type = (unsigned long) page->lru.next;
    BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
           type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);

    if (atomic_dec_return(&page->_count) == 1) {
        ClearPagePrivate(page);
        set_page_private(page, 0);
        INIT_LIST_HEAD(&page->lru);
        __free_pages_bootmem(page, 0);
    }

}

static void register_page_bootmem_info_section(unsigned long start_pfn)
{
    unsigned long *usemap, mapsize, section_nr, i;
    struct mem_section *ms;
    struct page *page, *memmap;

    section_nr = pfn_to_section_nr(start_pfn);
    ms = __nr_to_section(section_nr);

    /* Get section's memmap address */
    memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);

    /*
     * Get page for the memmap's phys address
     * XXX: need more consideration for sparse_vmemmap...
     */
    page = virt_to_page(memmap);
    mapsize = sizeof(struct page) * PAGES_PER_SECTION;
    mapsize = PAGE_ALIGN(mapsize) >> PAGE_SHIFT;

    /* remember memmap's page */
    for (i = 0; i < mapsize; i++, page++)
        get_page_bootmem(section_nr, page, SECTION_INFO);

    usemap = __nr_to_section(section_nr)->pageblock_flags;
    page = virt_to_page(usemap);

    mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;

    for (i = 0; i < mapsize; i++, page++)
        get_page_bootmem(section_nr, page, MIX_SECTION_INFO);

}

void register_page_bootmem_info_node(struct pglist_data *pgdat)
{
    unsigned long i, pfn, end_pfn, nr_pages;
    int node = pgdat->node_id;
    struct page *page;
    struct zone *zone;

    nr_pages = PAGE_ALIGN(sizeof(struct pglist_data)) >> PAGE_SHIFT;
    page = virt_to_page(pgdat);

    for (i = 0; i < nr_pages; i++, page++)
        get_page_bootmem(node, page, NODE_INFO);

    zone = &pgdat->node_zones[0];
    for (; zone < pgdat->node_zones + MAX_NR_ZONES - 1; zone++) {
        if (zone->wait_table) {
            nr_pages = zone->wait_table_hash_nr_entries
                * sizeof(wait_queue_head_t);
            nr_pages = PAGE_ALIGN(nr_pages) >> PAGE_SHIFT;
            page = virt_to_page(zone->wait_table);

            for (i = 0; i < nr_pages; i++, page++)
                get_page_bootmem(node, page, NODE_INFO);
        }
    }

    pfn = pgdat->node_start_pfn;
    end_pfn = pfn + pgdat->node_spanned_pages;

    /* register_section info */
    for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
        /*
         * Some platforms can assign the same pfn to multiple nodes - on
         * node0 as well as nodeN.  To avoid registering a pfn against
         * multiple nodes we check that this pfn does not already
         * reside in some other node.
         */
        if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))
            register_page_bootmem_info_section(pfn);
    }
}
#endif /* !CONFIG_SPARSEMEM_VMEMMAP */

static void grow_zone_span(struct zone *zone, unsigned long start_pfn,
               unsigned long end_pfn)
{
    unsigned long old_zone_end_pfn;

    zone_span_writelock(zone);

    old_zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
    if (start_pfn < zone->zone_start_pfn)
        zone->zone_start_pfn = start_pfn;

    zone->spanned_pages = max(old_zone_end_pfn, end_pfn) -
                zone->zone_start_pfn;

    zone_span_writeunlock(zone);
}

static void grow_pgdat_span(struct pglist_data *pgdat, unsigned long start_pfn,
                unsigned long end_pfn)
{
    unsigned long old_pgdat_end_pfn =
        pgdat->node_start_pfn + pgdat->node_spanned_pages;

    if (start_pfn < pgdat->node_start_pfn)
        pgdat->node_start_pfn = start_pfn;

    pgdat->node_spanned_pages = max(old_pgdat_end_pfn, end_pfn) -
                    pgdat->node_start_pfn;
}

static int __meminit __add_zone(struct zone *zone, unsigned long phys_start_pfn)
{
    struct pglist_data *pgdat = zone->zone_pgdat;
    int nr_pages = PAGES_PER_SECTION;
    int nid = pgdat->node_id;
    int zone_type;
    unsigned long flags;

    zone_type = zone - pgdat->node_zones;
    if (!zone->wait_table) {
        int ret;

        ret = init_currently_empty_zone(zone, phys_start_pfn,
                        nr_pages, MEMMAP_HOTPLUG);
        if (ret)
            return ret;
    }
    pgdat_resize_lock(zone->zone_pgdat, &flags);
    grow_zone_span(zone, phys_start_pfn, phys_start_pfn + nr_pages);
    grow_pgdat_span(zone->zone_pgdat, phys_start_pfn,
            phys_start_pfn + nr_pages);
    pgdat_resize_unlock(zone->zone_pgdat, &flags);
    memmap_init_zone(nr_pages, nid, zone_type,
             phys_start_pfn, MEMMAP_HOTPLUG);
    return 0;
}

static int __meminit __add_section(int nid, struct zone *zone,
                    unsigned long phys_start_pfn)
{
    int nr_pages = PAGES_PER_SECTION;
    int ret;

    if (pfn_valid(phys_start_pfn))
        return -EEXIST;

    ret = sparse_add_one_section(zone, phys_start_pfn, nr_pages);

    if (ret < 0)
        return ret;

    ret = __add_zone(zone, phys_start_pfn);

    if (ret < 0)
        return ret;

    return register_new_memory(nid, __pfn_to_section(phys_start_pfn));
}

#ifdef CONFIG_SPARSEMEM_VMEMMAP
static int __remove_section(struct zone *zone, struct mem_section *ms)
{
    /*
     * XXX: Freeing memmap with vmemmap is not implement yet.
     *      This should be removed later.
     */
    return -EBUSY;
}
#else
static int __remove_section(struct zone *zone, struct mem_section *ms)
{
    unsigned long flags;
    struct pglist_data *pgdat = zone->zone_pgdat;
    int ret = -EINVAL;

    if (!valid_section(ms))
        return ret;

    ret = unregister_memory_section(ms);
    if (ret)
        return ret;

    pgdat_resize_lock(pgdat, &flags);
    sparse_remove_one_section(zone, ms);
    pgdat_resize_unlock(pgdat, &flags);
    return 0;
}
#endif

/*
 * Reasonably generic function for adding memory.  It is
 * expected that archs that support memory hotplug will
 * call this function after deciding the zone to which to
 * add the new pages.
 */
int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
            unsigned long nr_pages)
{
    unsigned long i;
    int err = 0;
    int start_sec, end_sec;
    /* during initialize mem_map, align hot-added range to section */
    start_sec = pfn_to_section_nr(phys_start_pfn);
    end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);

    for (i = start_sec; i <= end_sec; i++) {
        err = __add_section(nid, zone, i << PFN_SECTION_SHIFT);

        /*
         * EEXIST is finally dealt with by ioresource collision
         * check. see add_memory() => register_memory_resource()
         * Warning will be printed if there is collision.
         */
        if (err && (err != -EEXIST))
            break;
        err = 0;
    }

    return err;
}
EXPORT_SYMBOL_GPL(__add_pages);

int __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
         unsigned long nr_pages)
{
    unsigned long i, ret = 0;
    int sections_to_remove;

    /*
     * We can only remove entire sections
     */
    BUG_ON(phys_start_pfn & ~PAGE_SECTION_MASK);
    BUG_ON(nr_pages % PAGES_PER_SECTION);

    release_mem_region(phys_start_pfn << PAGE_SHIFT, nr_pages * PAGE_SIZE);

    sections_to_remove = nr_pages / PAGES_PER_SECTION;
    for (i = 0; i < sections_to_remove; i++) {
        unsigned long pfn = phys_start_pfn + i*PAGES_PER_SECTION;
        ret = __remove_section(zone, __pfn_to_section(pfn));
        if (ret)
            break;
    }
    return ret;
}
EXPORT_SYMBOL_GPL(__remove_pages);

int set_online_page_callback(online_page_callback_t callback)
{
    int rc = -EINVAL;

    lock_memory_hotplug();

    if (online_page_callback == generic_online_page) {
        online_page_callback = callback;
        rc = 0;
    }

    unlock_memory_hotplug();

    return rc;
}
EXPORT_SYMBOL_GPL(set_online_page_callback);

int restore_online_page_callback(online_page_callback_t callback)
{
    int rc = -EINVAL;

    lock_memory_hotplug();

    if (online_page_callback == callback) {
        online_page_callback = generic_online_page;
        rc = 0;
    }

    unlock_memory_hotplug();

    return rc;
}
EXPORT_SYMBOL_GPL(restore_online_page_callback);

void __online_page_set_limits(struct page *page)
{
    unsigned long pfn = page_to_pfn(page);

    if (pfn >= num_physpages)
        num_physpages = pfn + 1;
}
EXPORT_SYMBOL_GPL(__online_page_set_limits);

void __online_page_increment_counters(struct page *page)
{
    totalram_pages++;

#ifdef CONFIG_HIGHMEM
    if (PageHighMem(page))
        totalhigh_pages++;
#endif
}
EXPORT_SYMBOL_GPL(__online_page_increment_counters);

void __online_page_free(struct page *page)
{
    ClearPageReserved(page);
    init_page_count(page);
    __free_page(page);
}
EXPORT_SYMBOL_GPL(__online_page_free);

static void generic_online_page(struct page *page)
{
    __online_page_set_limits(page);
    __online_page_increment_counters(page);
    __online_page_free(page);
}

static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
            void *arg)
{
    unsigned long i;
    unsigned long onlined_pages = *(unsigned long *)arg;
    struct page *page;
    if (PageReserved(pfn_to_page(start_pfn)))
        for (i = 0; i < nr_pages; i++) {
            page = pfn_to_page(start_pfn + i);
            (*online_page_callback)(page);
            onlined_pages++;
        }
    *(unsigned long *)arg = onlined_pages;
    return 0;
}


int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
{
    unsigned long onlined_pages = 0;
    struct zone *zone;
    int need_zonelists_rebuild = 0;
    int nid;
    int ret;
    struct memory_notify arg;

    lock_memory_hotplug();
    arg.start_pfn = pfn;
    arg.nr_pages = nr_pages;
    arg.status_change_nid = -1;

    nid = page_to_nid(pfn_to_page(pfn));
    if (node_present_pages(nid) == 0)
        arg.status_change_nid = nid;

    ret = memory_notify(MEM_GOING_ONLINE, &arg);
    ret = notifier_to_errno(ret);
    if (ret) {
        memory_notify(MEM_CANCEL_ONLINE, &arg);
        unlock_memory_hotplug();
        return ret;
    }
    /*
     * This doesn't need a lock to do pfn_to_page().
     * The section can't be removed here because of the
     * memory_block->state_mutex.
     */
    zone = page_zone(pfn_to_page(pfn));
    /*
     * If this zone is not populated, then it is not in zonelist.
     * This means the page allocator ignores this zone.
     * So, zonelist must be updated after online.
     */
    mutex_lock(&zonelists_mutex);
    if (!populated_zone(zone))
        need_zonelists_rebuild = 1;

    ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
        online_pages_range);
    if (ret) {
        mutex_unlock(&zonelists_mutex);
        printk(KERN_DEBUG "online_pages [mem %#010llx-%#010llx] failed\n",
               (unsigned long long) pfn << PAGE_SHIFT,
               (((unsigned long long) pfn + nr_pages)
                << PAGE_SHIFT) - 1);
        memory_notify(MEM_CANCEL_ONLINE, &arg);
        unlock_memory_hotplug();
        return ret;
    }

    zone->present_pages += onlined_pages;
    zone->zone_pgdat->node_present_pages += onlined_pages;
    if (onlined_pages) {
        node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
        if (need_zonelists_rebuild)
            build_all_zonelists(NULL, zone);
        else
            zone_pcp_update(zone);
    }

    mutex_unlock(&zonelists_mutex);

    init_per_zone_wmark_min();

    if (onlined_pages)
        kswapd_run(zone_to_nid(zone));

    vm_total_pages = nr_free_pagecache_pages();

    writeback_set_ratelimit();

    if (onlined_pages)
        memory_notify(MEM_ONLINE, &arg);
    unlock_memory_hotplug();

    return 0;
}
#endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */

/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
{
    struct pglist_data *pgdat;
    unsigned long zones_size[MAX_NR_ZONES] = {0};
    unsigned long zholes_size[MAX_NR_ZONES] = {0};
    unsigned long start_pfn = start >> PAGE_SHIFT;

    pgdat = arch_alloc_nodedata(nid);
    if (!pgdat)
        return NULL;

    arch_refresh_nodedata(nid, pgdat);

    /* we can use NODE_DATA(nid) from here */

    /* init node's zones as empty zones, we don't have any present pages.*/
    free_area_init_node(nid, zones_size, start_pfn, zholes_size);

    /*
     * The node we allocated has no zone fallback lists. For avoiding
     * to access not-initialized zonelist, build here.
     */
    mutex_lock(&zonelists_mutex);
    build_all_zonelists(pgdat, NULL);
    mutex_unlock(&zonelists_mutex);

    return pgdat;
}

static void rollback_node_hotadd(int nid, pg_data_t *pgdat)
{
    arch_refresh_nodedata(nid, NULL);
    arch_free_nodedata(pgdat);
    return;
}


/*
 * called by cpu_up() to online a node without onlined memory.
 */
int mem_online_node(int nid)
{
    pg_data_t   *pgdat;
    int ret;

    lock_memory_hotplug();
    pgdat = hotadd_new_pgdat(nid, 0);
    if (!pgdat) {
        ret = -ENOMEM;
        goto out;
    }
    node_set_online(nid);
    ret = register_one_node(nid);
    BUG_ON(ret);

out:
    unlock_memory_hotplug();
    return ret;
}

/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
int __ref add_memory(int nid, u64 start, u64 size)
{
    pg_data_t *pgdat = NULL;
    int new_pgdat = 0;
    struct resource *res;
    int ret;

    lock_memory_hotplug();

    res = register_memory_resource(start, size);
    ret = -EEXIST;
    if (!res)
        goto out;

    if (!node_online(nid)) {
        pgdat = hotadd_new_pgdat(nid, start);
        ret = -ENOMEM;
        if (!pgdat)
            goto error;
        new_pgdat = 1;
    }

    /* call arch's memory hotadd */
    ret = arch_add_memory(nid, start, size);

    if (ret < 0)
        goto error;

    /* we online node here. we can't roll back from here. */
    node_set_online(nid);

    if (new_pgdat) {
        ret = register_one_node(nid);
        /*
         * If sysfs file of new node can't create, cpu on the node
         * can't be hot-added. There is no rollback way now.
         * So, check by BUG_ON() to catch it reluctantly..
         */
        BUG_ON(ret);
    }

    /* create new memmap entry */
    firmware_map_add_hotplug(start, start + size, "System RAM");

    goto out;

error:
    /* rollback pgdat allocation and others */
    if (new_pgdat)
        rollback_node_hotadd(nid, pgdat);
    if (res)
        release_memory_resource(res);

out:
    unlock_memory_hotplug();
    return ret;
}
EXPORT_SYMBOL_GPL(add_memory);

#ifdef CONFIG_MEMORY_HOTREMOVE
/*
 * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy
 * set and the size of the free page is given by page_order(). Using this,
 * the function determines if the pageblock contains only free pages.
 * Due to buddy contraints, a free page at least the size of a pageblock will
 * be located at the start of the pageblock
 */
static inline int pageblock_free(struct page *page)
{
    return PageBuddy(page) && page_order(page) >= pageblock_order;
}

/* Return the start of the next active pageblock after a given page */
static struct page *next_active_pageblock(struct page *page)
{
    /* Ensure the starting page is pageblock-aligned */
    BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));

    /* If the entire pageblock is free, move to the end of free page */
    if (pageblock_free(page)) {
        int order;
        /* be careful. we don't have locks, page_order can be changed.*/
        order = page_order(page);
        if ((order < MAX_ORDER) && (order >= pageblock_order))
            return page + (1 << order);
    }

    return page + pageblock_nr_pages;
}

/* Checks if this range of memory is likely to be hot-removable. */
int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
{
    struct page *page = pfn_to_page(start_pfn);
    struct page *end_page = page + nr_pages;

    /* Check the starting page of each pageblock within the range */
    for (; page < end_page; page = next_active_pageblock(page)) {
        if (!is_pageblock_removable_nolock(page))
            return 0;
        cond_resched();
    }

    /* All pageblocks in the memory block are likely to be hot-removable */
    return 1;
}

/*
 * Confirm all pages in a range [start, end) is belongs to the same zone.
 */
static int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
{
    unsigned long pfn;
    struct zone *zone = NULL;
    struct page *page;
    int i;
    for (pfn = start_pfn;
         pfn < end_pfn;
         pfn += MAX_ORDER_NR_PAGES) {
        i = 0;
        /* This is just a CONFIG_HOLES_IN_ZONE check.*/
        while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i))
            i++;
        if (i == MAX_ORDER_NR_PAGES)
            continue;
        page = pfn_to_page(pfn + i);
        if (zone && page_zone(page) != zone)
            return 0;
        zone = page_zone(page);
    }
    return 1;
}

/*
 * Scanning pfn is much easier than scanning lru list.
 * Scan pfn from start to end and Find LRU page.
 */
static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
{
    unsigned long pfn;
    struct page *page;
    for (pfn = start; pfn < end; pfn++) {
        if (pfn_valid(pfn)) {
            page = pfn_to_page(pfn);
            if (PageLRU(page))
                return pfn;
        }
    }
    return 0;
}

#define NR_OFFLINE_AT_ONCE_PAGES    (256)
static int
do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
{
    unsigned long pfn;
    struct page *page;
    int move_pages = NR_OFFLINE_AT_ONCE_PAGES;
    int not_managed = 0;
    int ret = 0;
    LIST_HEAD(source);

    for (pfn = start_pfn; pfn < end_pfn && move_pages > 0; pfn++) {
        if (!pfn_valid(pfn))
            continue;
        page = pfn_to_page(pfn);
        if (!get_page_unless_zero(page))
            continue;
        /*
         * We can skip free pages. And we can only deal with pages on
         * LRU.
         */
        ret = isolate_lru_page(page);
        if (!ret) { /* Success */
            put_page(page);
            list_add_tail(&page->lru, &source);
            move_pages--;
            inc_zone_page_state(page, NR_ISOLATED_ANON +
                        page_is_file_cache(page));

        } else {
#ifdef CONFIG_DEBUG_VM
            printk(KERN_ALERT "removing pfn %lx from LRU failed\n",
                   pfn);
            dump_page(page);
#endif
            put_page(page);
            /* Because we don't have big zone->lock. we should
               check this again here. */
            if (page_count(page)) {
                not_managed++;
                ret = -EBUSY;
                break;
            }
        }
    }
    if (!list_empty(&source)) {
        if (not_managed) {
            putback_lru_pages(&source);
            goto out;
        }

        /*
         * alloc_migrate_target should be improooooved!!
         * migrate_pages returns # of failed pages.
         */
        ret = migrate_pages(&source, alloc_migrate_target, 0,
                            true, MIGRATE_SYNC);
        if (ret)
            putback_lru_pages(&source);
    }
out:
    return ret;
}

/*
 * remove from free_area[] and mark all as Reserved.
 */
static int
offline_isolated_pages_cb(unsigned long start, unsigned long nr_pages,
            void *data)
{
    __offline_isolated_pages(start, start + nr_pages);
    return 0;
}

static void
offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
{
    walk_system_ram_range(start_pfn, end_pfn - start_pfn, NULL,
                offline_isolated_pages_cb);
}

/*
 * Check all pages in range, recoreded as memory resource, are isolated.
 */
static int
check_pages_isolated_cb(unsigned long start_pfn, unsigned long nr_pages,
            void *data)
{
    int ret;
    long offlined = *(long *)data;
    ret = test_pages_isolated(start_pfn, start_pfn + nr_pages);
    offlined = nr_pages;
    if (!ret)
        *(long *)data += offlined;
    return ret;
}

static long
check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
{
    long offlined = 0;
    int ret;

    ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn, &offlined,
            check_pages_isolated_cb);
    if (ret < 0)
        offlined = (long)ret;
    return offlined;
}

static int __ref __offline_pages(unsigned long start_pfn,
          unsigned long end_pfn, unsigned long timeout)
{
    unsigned long pfn, nr_pages, expire;
    long offlined_pages;
    int ret, drain, retry_max, node;
    struct zone *zone;
    struct memory_notify arg;

    BUG_ON(start_pfn >= end_pfn);
    /* at least, alignment against pageblock is necessary */
    if (!IS_ALIGNED(start_pfn, pageblock_nr_pages))
        return -EINVAL;
    if (!IS_ALIGNED(end_pfn, pageblock_nr_pages))
        return -EINVAL;
    /* This makes hotplug much easier...and readable.
       we assume this for now. .*/
    if (!test_pages_in_a_zone(start_pfn, end_pfn))
        return -EINVAL;

    lock_memory_hotplug();

    zone = page_zone(pfn_to_page(start_pfn));
    node = zone_to_nid(zone);
    nr_pages = end_pfn - start_pfn;

    /* set above range as isolated */
    ret = start_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
    if (ret)
        goto out;

    arg.start_pfn = start_pfn;
    arg.nr_pages = nr_pages;
    arg.status_change_nid = -1;
    if (nr_pages >= node_present_pages(node))
        arg.status_change_nid = node;

    ret = memory_notify(MEM_GOING_OFFLINE, &arg);
    ret = notifier_to_errno(ret);
    if (ret)
        goto failed_removal;

    pfn = start_pfn;
    expire = jiffies + timeout;
    drain = 0;
    retry_max = 5;
repeat:
    /* start memory hot removal */
    ret = -EAGAIN;
    if (time_after(jiffies, expire))
        goto failed_removal;
    ret = -EINTR;
    if (signal_pending(current))
        goto failed_removal;
    ret = 0;
    if (drain) {
        lru_add_drain_all();
        cond_resched();
        drain_all_pages();
    }

    pfn = scan_lru_pages(start_pfn, end_pfn);
    if (pfn) { /* We have page on LRU */
        ret = do_migrate_range(pfn, end_pfn);
        if (!ret) {
            drain = 1;
            goto repeat;
        } else {
            if (ret < 0)
                if (--retry_max == 0)
                    goto failed_removal;
            yield();
            drain = 1;
            goto repeat;
        }
    }
    /* drain all zone's lru pagevec, this is asyncronous... */
    lru_add_drain_all();
    yield();
    /* drain pcp pages , this is synchrouns. */
    drain_all_pages();
    /* check again */
    offlined_pages = check_pages_isolated(start_pfn, end_pfn);
    if (offlined_pages < 0) {
        ret = -EBUSY;
        goto failed_removal;
    }
    printk(KERN_INFO "Offlined Pages %ld\n", offlined_pages);
    /* Ok, all of our target is islaoted.
       We cannot do rollback at this point. */
    offline_isolated_pages(start_pfn, end_pfn);
    /* reset pagetype flags and makes migrate type to be MOVABLE */
    undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
    /* removal success */
    zone->present_pages -= offlined_pages;
    zone->zone_pgdat->node_present_pages -= offlined_pages;
    totalram_pages -= offlined_pages;

    init_per_zone_wmark_min();

    if (!populated_zone(zone)) {
        zone_pcp_reset(zone);
        mutex_lock(&zonelists_mutex);
        build_all_zonelists(NULL, NULL);
        mutex_unlock(&zonelists_mutex);
    } else
        zone_pcp_update(zone);

    if (!node_present_pages(node)) {
        node_clear_state(node, N_HIGH_MEMORY);
        kswapd_stop(node);
    }

    vm_total_pages = nr_free_pagecache_pages();
    writeback_set_ratelimit();

    memory_notify(MEM_OFFLINE, &arg);
    unlock_memory_hotplug();
    return 0;

failed_removal:
    printk(KERN_INFO "memory offlining [mem %#010llx-%#010llx] failed\n",
           (unsigned long long) start_pfn << PAGE_SHIFT,
           ((unsigned long long) end_pfn << PAGE_SHIFT) - 1);
    memory_notify(MEM_CANCEL_OFFLINE, &arg);
    /* pushback to free area */
    undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);

out:
    unlock_memory_hotplug();
    return ret;
}

int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
    return __offline_pages(start_pfn, start_pfn + nr_pages, 120 * HZ);
}

int remove_memory(u64 start, u64 size)
{
    struct memory_block *mem = NULL;
    struct mem_section *section;
    unsigned long start_pfn, end_pfn;
    unsigned long pfn, section_nr;
    int ret;

    start_pfn = PFN_DOWN(start);
    end_pfn = start_pfn + PFN_DOWN(size);

    for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
        section_nr = pfn_to_section_nr(pfn);
        if (!present_section_nr(section_nr))
            continue;

        section = __nr_to_section(section_nr);
        /* same memblock? */
        if (mem)
            if ((section_nr >= mem->start_section_nr) &&
                (section_nr <= mem->end_section_nr))
                continue;

        mem = find_memory_block_hinted(section, mem);
        if (!mem)
            continue;

        ret = offline_memory_block(mem);
        if (ret) {
            kobject_put(&mem->dev.kobj);
            return ret;
        }
    }

    if (mem)
        kobject_put(&mem->dev.kobj);

    return 0;
}
#else
int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
    return -EINVAL;
}
int remove_memory(u64 start, u64 size)
{
    return -EINVAL;
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
EXPORT_SYMBOL_GPL(remove_memory);