mm/balloon_compaction.c

   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  */
  23 struct 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 }
  44 EXPORT_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  */
  57 struct 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 (!PagePrivate(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 }
 105 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
 106
 107 #ifdef CONFIG_BALLOON_COMPACTION
 108
 109 static inline void __isolate_balloon_page(struct page *page)
 110 {
 111         struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 112         unsigned long flags;
 113
 114         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 115         ClearPagePrivate(page);
 116         list_del(&page->lru);
 117         b_dev_info->isolated_pages++;
 118         spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 119 }
 120
 121 static inline void __putback_balloon_page(struct page *page)
 122 {
 123         struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 124         unsigned long flags;
 125
 126         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 127         SetPagePrivate(page);
 128         list_add(&page->lru, &b_dev_info->pages);
 129         b_dev_info->isolated_pages--;
 130         spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 131 }
 132
 133 /* __isolate_lru_page() counterpart for a ballooned page */
 134 bool balloon_page_isolate(struct page *page)
 135 {
 136         /*
 137          * Avoid burning cycles with pages that are yet under __free_pages(),
 138          * or just got freed under us.
 139          *
 140          * In case we 'win' a race for a balloon page being freed under us and
 141          * raise its refcount preventing __free_pages() from doing its job
 142          * the put_page() at the end of this block will take care of
 143          * release this page, thus avoiding a nasty leakage.
 144          */
 145         if (likely(get_page_unless_zero(page))) {
 146                 /*
 147                  * As balloon pages are not isolated from LRU lists, concurrent
 148                  * compaction threads can race against page migration functions
 149                  * as well as race against the balloon driver releasing a page.
 150                  *
 151                  * In order to avoid having an already isolated balloon page
 152                  * being (wrongly) re-isolated while it is under migration,
 153                  * or to avoid attempting to isolate pages being released by
 154                  * the balloon driver, lets be sure we have the page lock
 155                  * before proceeding with the balloon page isolation steps.
 156                  */
 157                 if (likely(trylock_page(page))) {
 158                         /*
 159                          * A ballooned page, by default, has PagePrivate set.
 160                          * Prevent concurrent compaction threads from isolating
 161                          * an already isolated balloon page by clearing it.
 162                          */
 163                         if (balloon_page_movable(page)) {
 164                                 __isolate_balloon_page(page);
 165                                 unlock_page(page);
 166                                 return true;
 167                         }
 168                         unlock_page(page);
 169                 }
 170                 put_page(page);
 171         }
 172         return false;
 173 }
 174
 175 /* putback_lru_page() counterpart for a ballooned page */
 176 void balloon_page_putback(struct page *page)
 177 {
 178         /*
 179          * 'lock_page()' stabilizes the page and prevents races against
 180          * concurrent isolation threads attempting to re-isolate it.
 181          */
 182         lock_page(page);
 183
 184         if (__is_movable_balloon_page(page)) {
 185                 __putback_balloon_page(page);
 186                 /* drop the extra ref count taken for page isolation */
 187                 put_page(page);
 188         } else {
 189                 WARN_ON(1);
 190                 dump_page(page, "not movable balloon page");
 191         }
 192         unlock_page(page);
 193 }
 194
 195 /* move_to_new_page() counterpart for a ballooned page */
 196 int balloon_page_migrate(struct page *newpage,
 197                          struct page *page, enum migrate_mode mode)
 198 {
 199         struct balloon_dev_info *balloon = balloon_page_device(page);
 200         int rc = -EAGAIN;
 201
 202         VM_BUG_ON_PAGE(!PageLocked(page), page);
 203         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 204
 205         if (WARN_ON(!__is_movable_balloon_page(page))) {
 206                 dump_page(page, "not movable balloon page");
 207                 return rc;
 208         }
 209
 210         if (balloon && balloon->migratepage)
 211                 rc = balloon->migratepage(balloon, newpage, page, mode);
 212
 213         return rc;
 214 }
 215 #endif /* CONFIG_BALLOON_COMPACTION */