linux/mm/balloon_compaction.c
Michael S. Tsirkin cfe61801b0 balloon: fix up comments
Lots of comments bitrotted. Fix them up.

Fixes: 418a3ab1e7 (mm/balloon_compaction: List interfaces)
Reviewed-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Acked-by: Nadav Amit <namit@vmware.com>
2019-07-22 11:19:26 -04:00

260 lines
8.2 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* mm/balloon_compaction.c
*
* Common interface for making balloon pages movable by compaction.
*
* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
*/
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/balloon_compaction.h>
static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
struct page *page)
{
/*
* Block others from accessing the 'page' when we get around to
* establishing additional references. We should be the only one
* holding a reference to the 'page' at this point. If we are not, then
* memory corruption is possible and we should stop execution.
*/
BUG_ON(!trylock_page(page));
balloon_page_insert(b_dev_info, page);
unlock_page(page);
__count_vm_event(BALLOON_INFLATE);
}
/**
* balloon_page_list_enqueue() - inserts a list of pages into the balloon page
* list.
* @b_dev_info: balloon device descriptor where we will insert a new page to
* @pages: pages to enqueue - allocated using balloon_page_alloc.
*
* Driver must call this function to properly enqueue balloon pages before
* definitively removing them from the guest system.
*
* Return: number of pages that were enqueued.
*/
size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
struct list_head *pages)
{
struct page *page, *tmp;
unsigned long flags;
size_t n_pages = 0;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
list_for_each_entry_safe(page, tmp, pages, lru) {
list_del(&page->lru);
balloon_page_enqueue_one(b_dev_info, page);
n_pages++;
}
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
return n_pages;
}
EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
/**
* balloon_page_list_dequeue() - removes pages from balloon's page list and
* returns a list of the pages.
* @b_dev_info: balloon device decriptor where we will grab a page from.
* @pages: pointer to the list of pages that would be returned to the caller.
* @n_req_pages: number of requested pages.
*
* Driver must call this function to properly de-allocate a previous enlisted
* balloon pages before definitively releasing it back to the guest system.
* This function tries to remove @n_req_pages from the ballooned pages and
* return them to the caller in the @pages list.
*
* Note that this function may fail to dequeue some pages even if the balloon
* isn't empty - since the page list can be temporarily empty due to compaction
* of isolated pages.
*
* Return: number of pages that were added to the @pages list.
*/
size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
struct list_head *pages, size_t n_req_pages)
{
struct page *page, *tmp;
unsigned long flags;
size_t n_pages = 0;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
if (n_pages == n_req_pages)
break;
/*
* Block others from accessing the 'page' while we get around to
* establishing additional references and preparing the 'page'
* to be released by the balloon driver.
*/
if (!trylock_page(page))
continue;
if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
PageIsolated(page)) {
/* raced with isolation */
unlock_page(page);
continue;
}
balloon_page_delete(page);
__count_vm_event(BALLOON_DEFLATE);
list_add(&page->lru, pages);
unlock_page(page);
n_pages++;
}
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
return n_pages;
}
EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
/*
* balloon_page_alloc - allocates a new page for insertion into the balloon
* page list.
*
* Driver must call this function to properly allocate a new balloon page.
* Driver must call balloon_page_enqueue before definitively removing the page
* from the guest system.
*
* Return: struct page for the allocated page or NULL on allocation failure.
*/
struct page *balloon_page_alloc(void)
{
struct page *page = alloc_page(balloon_mapping_gfp_mask() |
__GFP_NOMEMALLOC | __GFP_NORETRY);
return page;
}
EXPORT_SYMBOL_GPL(balloon_page_alloc);
/*
* balloon_page_enqueue - inserts a new page into the balloon page list.
*
* @b_dev_info: balloon device descriptor where we will insert a new page
* @page: new page to enqueue - allocated using balloon_page_alloc.
*
* Drivers must call this function to properly enqueue a new allocated balloon
* page before definitively removing the page from the guest system.
*
* Drivers must not call balloon_page_enqueue on pages that have been pushed to
* a list with balloon_page_push before removing them with balloon_page_pop. To
* enqueue a list of pages, use balloon_page_list_enqueue instead.
*/
void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
struct page *page)
{
unsigned long flags;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
balloon_page_enqueue_one(b_dev_info, page);
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}
EXPORT_SYMBOL_GPL(balloon_page_enqueue);
/*
* balloon_page_dequeue - removes a page from balloon's page list and returns
* its address to allow the driver to release the page.
* @b_dev_info: balloon device decriptor where we will grab a page from.
*
* Driver must call this function to properly dequeue a previously enqueued page
* before definitively releasing it back to the guest system.
*
* Caller must perform its own accounting to ensure that this
* function is called only if some pages are actually enqueued.
*
* Note that this function may fail to dequeue some pages even if there are
* some enqueued pages - since the page list can be temporarily empty due to
* the compaction of isolated pages.
*
* TODO: remove the caller accounting requirements, and allow caller to wait
* until all pages can be dequeued.
*
* Return: struct page for the dequeued page, or NULL if no page was dequeued.
*/
struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
{
unsigned long flags;
LIST_HEAD(pages);
int n_pages;
n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
if (n_pages != 1) {
/*
* If we are unable to dequeue a balloon page because the page
* list is empty and there are no isolated pages, then something
* went out of track and some balloon pages are lost.
* BUG() here, otherwise the balloon driver may get stuck in
* an infinite loop while attempting to release all its pages.
*/
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
if (unlikely(list_empty(&b_dev_info->pages) &&
!b_dev_info->isolated_pages))
BUG();
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
return NULL;
}
return list_first_entry(&pages, struct page, lru);
}
EXPORT_SYMBOL_GPL(balloon_page_dequeue);
#ifdef CONFIG_BALLOON_COMPACTION
bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
{
struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
list_del(&page->lru);
b_dev_info->isolated_pages++;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
return true;
}
void balloon_page_putback(struct page *page)
{
struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
list_add(&page->lru, &b_dev_info->pages);
b_dev_info->isolated_pages--;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}
/* move_to_new_page() counterpart for a ballooned page */
int balloon_page_migrate(struct address_space *mapping,
struct page *newpage, struct page *page,
enum migrate_mode mode)
{
struct balloon_dev_info *balloon = balloon_page_device(page);
/*
* We can not easily support the no copy case here so ignore it as it
* is unlikely to be used with balloon pages. See include/linux/hmm.h
* for a user of the MIGRATE_SYNC_NO_COPY mode.
*/
if (mode == MIGRATE_SYNC_NO_COPY)
return -EINVAL;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
return balloon->migratepage(balloon, newpage, page, mode);
}
const struct address_space_operations balloon_aops = {
.migratepage = balloon_page_migrate,
.isolate_page = balloon_page_isolate,
.putback_page = balloon_page_putback,
};
EXPORT_SYMBOL_GPL(balloon_aops);
#endif /* CONFIG_BALLOON_COMPACTION */