222 lines
6.8 KiB
C
Executable File
222 lines
6.8 KiB
C
Executable File
/*
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* mm/balloon_compaction.c
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*
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* Common interface for making balloon pages movable by compaction.
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*
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* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
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*/
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#include <linux/mm.h>
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#include <linux/slab.h>
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#include <linux/export.h>
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#include <linux/balloon_compaction.h>
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/*
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* balloon_page_enqueue - allocates a new page and inserts it into the balloon
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* page list.
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* @b_dev_info: balloon device decriptor where we will insert a new page to
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*
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* Driver must call it to properly allocate a new enlisted balloon page
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* before definetively removing it from the guest system.
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* This function returns the page address for the recently enqueued page or
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* NULL in the case we fail to allocate a new page this turn.
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*/
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struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
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{
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unsigned long flags;
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struct page *page = alloc_page(balloon_mapping_gfp_mask() |
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__GFP_NOMEMALLOC | __GFP_NORETRY);
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if (!page)
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return NULL;
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/*
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* Block others from accessing the 'page' when we get around to
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* establishing additional references. We should be the only one
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* holding a reference to the 'page' at this point.
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*/
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BUG_ON(!trylock_page(page));
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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balloon_page_insert(b_dev_info, page);
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__count_vm_event(BALLOON_INFLATE);
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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unlock_page(page);
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return page;
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}
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EXPORT_SYMBOL_GPL(balloon_page_enqueue);
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/*
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* balloon_page_dequeue - removes a page from balloon's page list and returns
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* the its address to allow the driver release the page.
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* @b_dev_info: balloon device decriptor where we will grab a page from.
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*
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* Driver must call it to properly de-allocate a previous enlisted balloon page
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* before definetively releasing it back to the guest system.
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* This function returns the page address for the recently dequeued page or
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* NULL in the case we find balloon's page list temporarily empty due to
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* compaction isolated pages.
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*/
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struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
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{
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struct page *page, *tmp;
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unsigned long flags;
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bool dequeued_page;
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dequeued_page = false;
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list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
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/*
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* Block others from accessing the 'page' while we get around
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* establishing additional references and preparing the 'page'
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* to be released by the balloon driver.
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*/
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if (trylock_page(page)) {
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#ifdef CONFIG_BALLOON_COMPACTION
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if (!PagePrivate(page)) {
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/* raced with isolation */
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unlock_page(page);
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continue;
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}
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#endif
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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balloon_page_delete(page);
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__count_vm_event(BALLOON_DEFLATE);
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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unlock_page(page);
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dequeued_page = true;
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break;
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}
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}
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if (!dequeued_page) {
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/*
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* If we are unable to dequeue a balloon page because the page
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* list is empty and there is no isolated pages, then something
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* went out of track and some balloon pages are lost.
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* BUG() here, otherwise the balloon driver may get stuck into
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* an infinite loop while attempting to release all its pages.
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*/
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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if (unlikely(list_empty(&b_dev_info->pages) &&
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!b_dev_info->isolated_pages))
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BUG();
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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page = NULL;
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}
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return page;
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}
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EXPORT_SYMBOL_GPL(balloon_page_dequeue);
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#ifdef CONFIG_BALLOON_COMPACTION
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static inline void __isolate_balloon_page(struct page *page)
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{
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struct balloon_dev_info *b_dev_info = balloon_page_device(page);
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unsigned long flags;
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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ClearPagePrivate(page);
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list_del(&page->lru);
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b_dev_info->isolated_pages++;
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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}
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static inline void __putback_balloon_page(struct page *page)
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{
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struct balloon_dev_info *b_dev_info = balloon_page_device(page);
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unsigned long flags;
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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SetPagePrivate(page);
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list_add(&page->lru, &b_dev_info->pages);
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b_dev_info->isolated_pages--;
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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}
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/* __isolate_lru_page() counterpart for a ballooned page */
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bool balloon_page_isolate(struct page *page)
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{
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/*
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* Avoid burning cycles with pages that are yet under __free_pages(),
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* or just got freed under us.
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*
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* In case we 'win' a race for a balloon page being freed under us and
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* raise its refcount preventing __free_pages() from doing its job
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* the put_page() at the end of this block will take care of
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* release this page, thus avoiding a nasty leakage.
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*/
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if (likely(get_page_unless_zero(page))) {
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/*
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* As balloon pages are not isolated from LRU lists, concurrent
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* compaction threads can race against page migration functions
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* as well as race against the balloon driver releasing a page.
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*
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* In order to avoid having an already isolated balloon page
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* being (wrongly) re-isolated while it is under migration,
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* or to avoid attempting to isolate pages being released by
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* the balloon driver, lets be sure we have the page lock
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* before proceeding with the balloon page isolation steps.
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*/
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if (likely(trylock_page(page))) {
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/*
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* A ballooned page, by default, has PagePrivate set.
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* Prevent concurrent compaction threads from isolating
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* an already isolated balloon page by clearing it.
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*/
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if (balloon_page_movable(page)) {
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__isolate_balloon_page(page);
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unlock_page(page);
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return true;
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}
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unlock_page(page);
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}
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put_page(page);
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}
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return false;
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}
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/* putback_lru_page() counterpart for a ballooned page */
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void balloon_page_putback(struct page *page)
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{
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/*
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* 'lock_page()' stabilizes the page and prevents races against
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* concurrent isolation threads attempting to re-isolate it.
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*/
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lock_page(page);
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if (__is_movable_balloon_page(page)) {
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__putback_balloon_page(page);
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/* drop the extra ref count taken for page isolation */
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put_page(page);
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} else {
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WARN_ON(1);
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dump_page(page, "not movable balloon page");
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}
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unlock_page(page);
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}
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/* move_to_new_page() counterpart for a ballooned page */
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int balloon_page_migrate(struct page *newpage,
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struct page *page, enum migrate_mode mode)
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{
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struct balloon_dev_info *balloon = balloon_page_device(page);
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int rc = -EAGAIN;
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/*
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* Block others from accessing the 'newpage' when we get around to
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* establishing additional references. We should be the only one
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* holding a reference to the 'newpage' at this point.
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*/
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BUG_ON(!trylock_page(newpage));
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if (WARN_ON(!__is_movable_balloon_page(page))) {
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dump_page(page, "not movable balloon page");
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unlock_page(newpage);
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return rc;
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}
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if (balloon && balloon->migratepage)
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rc = balloon->migratepage(balloon, newpage, page, mode);
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unlock_page(newpage);
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return rc;
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}
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#endif /* CONFIG_BALLOON_COMPACTION */
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