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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Common interface for implementing a memory balloon, including support
* for migration of pages inflated in a memory balloon.
*
* Balloon page migration makes use of the general "movable_ops page migration"
* feature.
*
* page->private is used to reference the responsible balloon device.
* That these pages have movable_ops, and which movable_ops apply,
* is derived from the page type (PageOffline()) combined with the
* PG_movable_ops flag (PageMovableOps()).
*
* Once the page type and the PG_movable_ops are set, migration code
* can initiate page isolation by invoking the
* movable_operations()->isolate_page() callback
*
* As long as page->private is set, the page is either on the balloon list
* or isolated for migration. If page->private is not set, the page is
* either still getting inflated, or was deflated to be freed by the balloon
* driver soon. Isolation is impossible in both cases.
*
* 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 migration. In order to sort out these racy scenarios
* and safely perform balloon's page migration we must, always, ensure following
* these simple rules:
*
* i. Inflation/deflation must set/clear page->private under the
* balloon_pages_lock
*
* ii. isolation or dequeueing procedure must remove the page from balloon
* device page list under balloon_pages_lock
*
* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
*/
#ifndef _LINUX_BALLOON_H
#define _LINUX_BALLOON_H
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/migrate.h>
#include <linux/gfp.h>
#include <linux/err.h>
#include <linux/list.h>
/*
* Balloon device information descriptor.
* This struct is used to allow the common balloon page migration interface
* procedures to find the proper balloon device holding memory pages they'll
* have to cope for page 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 */
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);
bool adjust_managed_page_count;
};
struct page *balloon_page_alloc(void);
void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
struct page *page);
struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
struct list_head *pages);
size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
struct list_head *pages, size_t n_req_pages);
static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
{
balloon->isolated_pages = 0;
INIT_LIST_HEAD(&balloon->pages);
balloon->migratepage = NULL;
balloon->adjust_managed_page_count = false;
}
#endif /* _LINUX_BALLOON_H */
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