/*
* include/linux/balloon_compaction.h
*
* Common interface definitions for making balloon pages movable by compaction.
*
* Despite being perfectly possible to perform ballooned pages migration, they
* make a special corner case to compaction scans because balloon pages are not
* enlisted at any LRU list like the other pages we do compact / migrate.
*
* As the page isolation scanning step a compaction thread does is a lockless
* procedure (from a page standpoint), it might bring some racy situations while
* performing balloon page compaction. In order to sort out these racy scenarios
* and safely perform balloon's page compaction and migration we must, always,
* ensure following these three simple rules:
*
* i. when updating a balloon's page ->mapping element, strictly do it under
* the following lock order, independently of the far superior
* locking scheme (lru_lock, balloon_lock):
* +-page_lock(page);
* +--spin_lock_irq(&b_dev_info->pages_lock);
* ... page->mapping updates here ...
*
* ii. before isolating or dequeueing a balloon page from the balloon device
* pages list, the page reference counter must be raised by one and the
* extra refcount must be dropped when the page is enqueued back into
* the balloon device page list, thus a balloon page keeps its reference
* counter raised only while it is under our special handling;
*
* iii. after the lockless scan step have selected a potential balloon page for
* isolation, re-test the PageBalloon mark and the PagePrivate flag
* under the proper page lock, to ensure isolating a valid balloon page
* (not yet isolated, nor under release procedure)
*
* iv. isolation or dequeueing procedure must clear PagePrivate flag under
* page lock together with removing page from balloon device page list.
*
* The functions provided by this interface are placed to help on coping with
* the aforementioned balloon page corner case, as well as to ensure the simple
* set of exposed rules are satisfied while we are dealing with balloon pages
* compaction / migration.
*
* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
*/
#ifndef _LINUX_BALLOON_COMPACTION_H
#define _LINUX_BALLOON_COMPACTION_H
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/migrate.h>
#include <linux/gfp.h>
#include <linux/err.h>
/*
* Balloon device information descriptor.
* This struct is used to allow the common balloon compaction interface
* procedures to find the proper balloon device holding memory pages they'll
* have to cope for page compaction / migration, as well as it serves the
* balloon driver as a page book-keeper for its registered balloon devices.
*/
struct balloon_dev_info {
unsigned long isolated_pages; /* # of isolated pages for migration */
spinlock_t pages_lock; /* Protection to pages list */
struct list_head pages; /* Pages enqueued & handled to Host */
int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
struct page *page, enum migrate_mode mode);
};
extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
{
balloon->isolated_pages = 0;
spin_lock_init(&balloon->pages_lock);
INIT_LIST_HEAD(&balloon->pages);
balloon->migratepage = NULL;
}
#ifdef CONFIG_BALLOON_COMPACTION
extern bool balloon_page_isolate(struct page *page);
extern void balloon_page_putback(struct page *page);
extern int balloon_page_migrate(struct page *newpage,
struct page *page, enum migrate_mode mode);
/*
* __is_movable_balloon_page - helper to perform @page PageBalloon tests
*/
static inline bool __is_movable_balloon_page(struct page *page)
{
return PageBalloon(page);
}
/*
* balloon_page_movable - test PageBalloon to identify balloon pages
* and PagePrivate to check that the page is not
* isolated and can be moved by compaction/migration.
*
* As we might return false positives in the case of a balloon page being just
* released under us, this need to be re-tested later, under the page lock.
*/
static inline bool balloon_page_movable(struct page *page)
{
return PageBalloon(page) && PagePrivate(page);
}
/*
* isolated_balloon_page - identify an isolated balloon page on private
* compaction/migration page lists.
*/
static inline bool isolated_balloon_page(struct page *page)
{
return PageBalloon(page);
}
/*
* balloon_page_insert - insert a page into the balloon's page list and make
* the page->private assignment accordingly.
* @balloon : pointer to balloon device
* @page : page to be assigned as a 'balloon page'
*
* Caller must ensure the page is locked and the spin_lock protecting balloon
* pages list is held before inserting a page into the balloon device.
*/
static inline void balloon_page_insert(struct balloon_dev_info *balloon,
struct page *page)
{
__SetPageBalloon(page);
SetPagePrivate(page);
set_page_private(page, (unsigned long)balloon);
list_add(&page->lru, &balloon->pages);
}
/*
* balloon_page_delete - delete a page from balloon's page list and clear
* the page->private assignement accordingly.
* @page : page to be released from balloon's page list
*
* Caller must ensure the page is locked and the spin_lock protecting balloon
* pages list is held before deleting a page from the balloon device.
*/
static inline void balloon_page_delete(struct page *page)
{
__ClearPageBalloon(page);
set_page_private(page, 0);
if (PagePrivate(page)) {
ClearPagePrivate(page);
list_del(&page->lru);
}
}
/*
* balloon_page_device - get the b_dev_info descriptor for the balloon device
* that enqueues the given page.
*/
static inline struct balloon_dev_info *balloon_page_device(struct page *page)
{
return (struct balloon_dev_info *)page_private(page);
}
static inline gfp_t balloon_mapping_gfp_mask(void)
{
return GFP_HIGHUSER_MOVABLE;
}
#else /* !CONFIG_BALLOON_COMPACTION */
static inline void balloon_page_insert(struct balloon_dev_info *balloon,
struct page *page)
{
__SetPageBalloon(page);
list_add(&page->lru, &balloon->pages);
}
static inline void balloon_page_delete(struct page *page)
{
__ClearPageBalloon(page);
list_del(&page->lru);
}
static inline bool __is_movable_balloon_page(struct page *page)
{
return false;
}
static inline bool balloon_page_movable(struct page *page)
{
return false;
}
static inline bool isolated_balloon_page(struct page *page)
{
return false;
}
static inline bool balloon_page_isolate(struct page *page)
{
return false;
}
static inline void balloon_page_putback(struct page *page)
{
return;
}
static inline int balloon_page_migrate(struct page *newpage,
struct page *page, enum migrate_mode mode)
{
return 0;
}
static inline gfp_t balloon_mapping_gfp_mask(void)
{
return GFP_HIGHUSER;
}
#endif /* CONFIG_BALLOON_COMPACTION */
#endif /* _LINUX_BALLOON_COMPACTION_H */