linux/mm/balloon_compaction.c
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   1/*
   2 * mm/balloon_compaction.c
   3 *
   4 * Common interface for making balloon pages movable by compaction.
   5 *
   6 * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
   7 */
   8#include <linux/mm.h>
   9#include <linux/slab.h>
  10#include <linux/export.h>
  11#include <linux/balloon_compaction.h>
  12
  13/*
  14 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
  15 *                        page list.
  16 * @b_dev_info: balloon device descriptor where we will insert a new page to
  17 *
  18 * Driver must call it to properly allocate a new enlisted balloon page
  19 * before definitively removing it from the guest system.
  20 * This function returns the page address for the recently enqueued page or
  21 * NULL in the case we fail to allocate a new page this turn.
  22 */
  23struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
  24{
  25        unsigned long flags;
  26        struct page *page = alloc_page(balloon_mapping_gfp_mask() |
  27                                        __GFP_NOMEMALLOC | __GFP_NORETRY);
  28        if (!page)
  29                return NULL;
  30
  31        /*
  32         * Block others from accessing the 'page' when we get around to
  33         * establishing additional references. We should be the only one
  34         * holding a reference to the 'page' at this point.
  35         */
  36        BUG_ON(!trylock_page(page));
  37        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  38        balloon_page_insert(b_dev_info, page);
  39        __count_vm_event(BALLOON_INFLATE);
  40        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  41        unlock_page(page);
  42        return page;
  43}
  44EXPORT_SYMBOL_GPL(balloon_page_enqueue);
  45
  46/*
  47 * balloon_page_dequeue - removes a page from balloon's page list and returns
  48 *                        the its address to allow the driver release the page.
  49 * @b_dev_info: balloon device decriptor where we will grab a page from.
  50 *
  51 * Driver must call it to properly de-allocate a previous enlisted balloon page
  52 * before definetively releasing it back to the guest system.
  53 * This function returns the page address for the recently dequeued page or
  54 * NULL in the case we find balloon's page list temporarily empty due to
  55 * compaction isolated pages.
  56 */
  57struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
  58{
  59        struct page *page, *tmp;
  60        unsigned long flags;
  61        bool dequeued_page;
  62
  63        dequeued_page = false;
  64        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  65        list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
  66                /*
  67                 * Block others from accessing the 'page' while we get around
  68                 * establishing additional references and preparing the 'page'
  69                 * to be released by the balloon driver.
  70                 */
  71                if (trylock_page(page)) {
  72#ifdef CONFIG_BALLOON_COMPACTION
  73                        if (PageIsolated(page)) {
  74                                /* raced with isolation */
  75                                unlock_page(page);
  76                                continue;
  77                        }
  78#endif
  79                        balloon_page_delete(page);
  80                        __count_vm_event(BALLOON_DEFLATE);
  81                        unlock_page(page);
  82                        dequeued_page = true;
  83                        break;
  84                }
  85        }
  86        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  87
  88        if (!dequeued_page) {
  89                /*
  90                 * If we are unable to dequeue a balloon page because the page
  91                 * list is empty and there is no isolated pages, then something
  92                 * went out of track and some balloon pages are lost.
  93                 * BUG() here, otherwise the balloon driver may get stuck into
  94                 * an infinite loop while attempting to release all its pages.
  95                 */
  96                spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  97                if (unlikely(list_empty(&b_dev_info->pages) &&
  98                             !b_dev_info->isolated_pages))
  99                        BUG();
 100                spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 101                page = NULL;
 102        }
 103        return page;
 104}
 105EXPORT_SYMBOL_GPL(balloon_page_dequeue);
 106
 107#ifdef CONFIG_BALLOON_COMPACTION
 108
 109bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
 110
 111{
 112        struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 113        unsigned long flags;
 114
 115        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 116        list_del(&page->lru);
 117        b_dev_info->isolated_pages++;
 118        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 119
 120        return true;
 121}
 122
 123void balloon_page_putback(struct page *page)
 124{
 125        struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 126        unsigned long flags;
 127
 128        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 129        list_add(&page->lru, &b_dev_info->pages);
 130        b_dev_info->isolated_pages--;
 131        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 132}
 133
 134
 135/* move_to_new_page() counterpart for a ballooned page */
 136int balloon_page_migrate(struct address_space *mapping,
 137                struct page *newpage, struct page *page,
 138                enum migrate_mode mode)
 139{
 140        struct balloon_dev_info *balloon = balloon_page_device(page);
 141
 142        VM_BUG_ON_PAGE(!PageLocked(page), page);
 143        VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 144
 145        return balloon->migratepage(balloon, newpage, page, mode);
 146}
 147
 148const struct address_space_operations balloon_aops = {
 149        .migratepage = balloon_page_migrate,
 150        .isolate_page = balloon_page_isolate,
 151        .putback_page = balloon_page_putback,
 152};
 153EXPORT_SYMBOL_GPL(balloon_aops);
 154
 155#endif /* CONFIG_BALLOON_COMPACTION */
 156