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mm/balloon_compaction: use a device-independent balloon (list) lock

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In order to remove the dependency on the page lock for balloon pages, we
need a lock that is independent of the page.

It's crucial that we can handle the scenario where balloon deflation
(clearing page->private) can race with page isolation (using page->private
to obtain the balloon_dev_info where the lock currently resides).

The current lock in balloon_dev_info is therefore not suitable.

Fortunately, we never really have more than a single balloon device per
VM, so we can just keep it simple and use a static lock to protect all
balloon devices.

Based on this change we will remove the dependency on the page lock next.

Link: https://lkml.kernel.org/r/20260119230133.3551867-9-david@kernel.org
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Jerrin Shaji George <jerrin.shaji-george@broadcom.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand (Red Hat)
2026-01-20 00:01:16 +01:00
committed by Andrew Morton
parent c33b47c334
commit 8202313e3d
2 changed files with 22 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/balloon_compaction.h
View File

@@ -21,10 +21,10 @@
* i. Setting the PG_movable_ops flag and page->private with the following
* lock order
* +-page_lock(page);
* +--spin_lock_irq(&b_dev_info->pages_lock);
* +--spin_lock_irq(&balloon_pages_lock);
*
* ii. isolation or dequeueing procedure must remove the page from balloon
* device page list under b_dev_info->pages_lock.
* device page list under balloon_pages_lock
*
* 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
@@ -52,7 +52,6 @@
*/
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);
@@ -71,7 +70,6 @@ extern size_t balloon_page_list_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;
balloon->adjust_managed_page_count = false;

34
mm/balloon_compaction.c
View File

@@ -11,6 +11,12 @@
#include <linux/export.h>
#include <linux/balloon_compaction.h>
/*
* Lock protecting the balloon_dev_info of all devices. We don't really
* expect more than one device.
*/
static DEFINE_SPINLOCK(balloon_pages_lock);
static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
struct page *page)
{
@@ -47,13 +53,13 @@ size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
unsigned long flags;
size_t n_pages = 0;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_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);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
return n_pages;
}
EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
@@ -83,7 +89,7 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
unsigned long flags;
size_t n_pages = 0;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_pages_lock, flags);
list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
if (n_pages == n_req_pages)
break;
@@ -106,7 +112,7 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
dec_node_page_state(page, NR_BALLOON_PAGES);
n_pages++;
}
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
return n_pages;
}
@@ -149,9 +155,9 @@ void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
{
unsigned long flags;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_pages_lock, flags);
balloon_page_enqueue_one(b_dev_info, page);
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
}
EXPORT_SYMBOL_GPL(balloon_page_enqueue);
@@ -191,11 +197,11 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
* 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);
spin_lock_irqsave(&balloon_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);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
return NULL;
}
return list_first_entry(&pages, struct page, lru);
@@ -213,10 +219,10 @@ static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
if (!b_dev_info)
return false;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_pages_lock, flags);
list_del(&page->lru);
b_dev_info->isolated_pages++;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
return true;
}
@@ -234,10 +240,10 @@ static void balloon_page_putback(struct page *page)
if (WARN_ON_ONCE(!b_dev_info))
return;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_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);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
}
static int balloon_page_migrate(struct page *newpage, struct page *page,
@@ -262,7 +268,7 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,
if (rc < 0 && rc != -ENOENT)
return rc;
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
spin_lock_irqsave(&balloon_pages_lock, flags);
if (!rc) {
/* Insert the new page into the balloon list. */
get_page(newpage);
@@ -287,7 +293,7 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,
}
b_dev_info->isolated_pages--;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
spin_unlock_irqrestore(&balloon_pages_lock, flags);
/* Free the now-deflated page we isolated in balloon_page_isolate(). */
balloon_page_finalize(page);