273 lines
8.9 KiB
C
273 lines
8.9 KiB
C
/*
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* include/linux/balloon_compaction.h
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*
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* Common interface definitions for making balloon pages movable by compaction.
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*
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* Despite being perfectly possible to perform ballooned pages migration, they
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* make a special corner case to compaction scans because balloon pages are not
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* enlisted at any LRU list like the other pages we do compact / migrate.
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*
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* As the page isolation scanning step a compaction thread does is a lockless
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* procedure (from a page standpoint), it might bring some racy situations while
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* performing balloon page compaction. In order to sort out these racy scenarios
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* and safely perform balloon's page compaction and migration we must, always,
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* ensure following these three simple rules:
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*
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* i. when updating a balloon's page ->mapping element, strictly do it under
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* the following lock order, independently of the far superior
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* locking scheme (lru_lock, balloon_lock):
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* +-page_lock(page);
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* +--spin_lock_irq(&b_dev_info->pages_lock);
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* ... page->mapping updates here ...
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*
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* ii. before isolating or dequeueing a balloon page from the balloon device
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* pages list, the page reference counter must be raised by one and the
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* extra refcount must be dropped when the page is enqueued back into
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* the balloon device page list, thus a balloon page keeps its reference
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* counter raised only while it is under our special handling;
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*
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* iii. after the lockless scan step have selected a potential balloon page for
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* isolation, re-test the page->mapping flags and the page ref counter
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* under the proper page lock, to ensure isolating a valid balloon page
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* (not yet isolated, nor under release procedure)
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*
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* The functions provided by this interface are placed to help on coping with
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* the aforementioned balloon page corner case, as well as to ensure the simple
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* set of exposed rules are satisfied while we are dealing with balloon pages
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* compaction / migration.
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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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#ifndef _LINUX_BALLOON_COMPACTION_H
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#define _LINUX_BALLOON_COMPACTION_H
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#include <linux/pagemap.h>
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#include <linux/page-flags.h>
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#include <linux/migrate.h>
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#include <linux/gfp.h>
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#include <linux/err.h>
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/*
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* Balloon device information descriptor.
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* This struct is used to allow the common balloon compaction interface
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* procedures to find the proper balloon device holding memory pages they'll
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* have to cope for page compaction / migration, as well as it serves the
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* balloon driver as a page book-keeper for its registered balloon devices.
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*/
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struct balloon_dev_info {
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void *balloon_device; /* balloon device descriptor */
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struct address_space *mapping; /* balloon special page->mapping */
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unsigned long isolated_pages; /* # of isolated pages for migration */
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spinlock_t pages_lock; /* Protection to pages list */
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struct list_head pages; /* Pages enqueued & handled to Host */
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};
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extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
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extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
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extern struct balloon_dev_info *balloon_devinfo_alloc(
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void *balloon_dev_descriptor);
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static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info)
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{
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kfree(b_dev_info);
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}
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/*
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* balloon_page_free - release a balloon page back to the page free lists
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* @page: ballooned page to be set free
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*
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* This function must be used to properly set free an isolated/dequeued balloon
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* page at the end of a sucessful page migration, or at the balloon driver's
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* page release procedure.
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*/
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static inline void balloon_page_free(struct page *page)
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{
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/*
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* Balloon pages always get an extra refcount before being isolated
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* and before being dequeued to help on sorting out fortuite colisions
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* between a thread attempting to isolate and another thread attempting
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* to release the very same balloon page.
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*
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* Before we handle the page back to Buddy, lets drop its extra refcnt.
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*/
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put_page(page);
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__free_page(page);
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}
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#ifdef CONFIG_BALLOON_COMPACTION
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extern bool balloon_page_isolate(struct page *page);
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extern void balloon_page_putback(struct page *page);
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extern int balloon_page_migrate(struct page *newpage,
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struct page *page, enum migrate_mode mode);
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extern struct address_space
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*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
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const struct address_space_operations *a_ops);
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static inline void balloon_mapping_free(struct address_space *balloon_mapping)
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{
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kfree(balloon_mapping);
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}
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/*
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* page_flags_cleared - helper to perform balloon @page ->flags tests.
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*
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* As balloon pages are obtained from buddy and we do not play with page->flags
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* at driver level (exception made when we get the page lock for compaction),
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* we can safely identify a ballooned page by checking if the
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* PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared. This approach also
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* helps us skip ballooned pages that are locked for compaction or release, thus
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* mitigating their racy check at balloon_page_movable()
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*/
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static inline bool page_flags_cleared(struct page *page)
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{
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return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP);
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}
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/*
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* __is_movable_balloon_page - helper to perform @page mapping->flags tests
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*/
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static inline bool __is_movable_balloon_page(struct page *page)
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{
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struct address_space *mapping = page->mapping;
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return mapping_balloon(mapping);
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}
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/*
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* balloon_page_movable - test page->mapping->flags to identify balloon pages
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* that can be moved by compaction/migration.
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*
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* This function is used at core compaction's page isolation scheme, therefore
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* most pages exposed to it are not enlisted as balloon pages and so, to avoid
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* undesired side effects like racing against __free_pages(), we cannot afford
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* holding the page locked while testing page->mapping->flags here.
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*
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* As we might return false positives in the case of a balloon page being just
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* released under us, the page->mapping->flags need to be re-tested later,
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* under the proper page lock, at the functions that will be coping with the
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* balloon page case.
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*/
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static inline bool balloon_page_movable(struct page *page)
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{
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/*
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* Before dereferencing and testing mapping->flags, let's make sure
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* this is not a page that uses ->mapping in a different way
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*/
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if (page_flags_cleared(page) && !page_mapped(page) &&
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page_count(page) == 1)
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return __is_movable_balloon_page(page);
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return false;
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}
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/*
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* balloon_page_insert - insert a page into the balloon's page list and make
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* the page->mapping assignment accordingly.
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* @page : page to be assigned as a 'balloon page'
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* @mapping : allocated special 'balloon_mapping'
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* @head : balloon's device page list head
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*
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* Caller must ensure the page is locked and the spin_lock protecting balloon
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* pages list is held before inserting a page into the balloon device.
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*/
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static inline void balloon_page_insert(struct page *page,
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struct address_space *mapping,
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struct list_head *head)
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{
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page->mapping = mapping;
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list_add(&page->lru, head);
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}
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/*
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* balloon_page_delete - delete a page from balloon's page list and clear
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* the page->mapping assignement accordingly.
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* @page : page to be released from balloon's page list
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*
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* Caller must ensure the page is locked and the spin_lock protecting balloon
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* pages list is held before deleting a page from the balloon device.
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*/
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static inline void balloon_page_delete(struct page *page)
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{
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page->mapping = NULL;
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list_del(&page->lru);
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}
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/*
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* balloon_page_device - get the b_dev_info descriptor for the balloon device
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* that enqueues the given page.
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*/
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static inline struct balloon_dev_info *balloon_page_device(struct page *page)
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{
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struct address_space *mapping = page->mapping;
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if (likely(mapping))
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return mapping->private_data;
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return NULL;
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}
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static inline gfp_t balloon_mapping_gfp_mask(void)
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{
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return GFP_HIGHUSER_MOVABLE;
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}
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static inline bool balloon_compaction_check(void)
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{
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return true;
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}
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#else /* !CONFIG_BALLOON_COMPACTION */
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static inline void *balloon_mapping_alloc(void *balloon_device,
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const struct address_space_operations *a_ops)
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{
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return ERR_PTR(-EOPNOTSUPP);
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}
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static inline void balloon_mapping_free(struct address_space *balloon_mapping)
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{
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return;
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}
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static inline void balloon_page_insert(struct page *page,
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struct address_space *mapping,
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struct list_head *head)
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{
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list_add(&page->lru, head);
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}
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static inline void balloon_page_delete(struct page *page)
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{
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list_del(&page->lru);
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}
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static inline bool balloon_page_movable(struct page *page)
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{
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return false;
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}
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static inline bool balloon_page_isolate(struct page *page)
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{
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return false;
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}
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static inline void balloon_page_putback(struct page *page)
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{
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return;
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}
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static inline 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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return 0;
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}
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static inline gfp_t balloon_mapping_gfp_mask(void)
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{
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return GFP_HIGHUSER;
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}
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static inline bool balloon_compaction_check(void)
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{
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return false;
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}
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#endif /* CONFIG_BALLOON_COMPACTION */
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#endif /* _LINUX_BALLOON_COMPACTION_H */
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