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[2003:d8:2f4e:3200:c99d:a38b:3f3a:d4b3]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-471556e17afsm190432085e9.17.2025.10.21.05.59.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Oct 2025 05:59:47 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Broadcom internal kernel review list , linux-doc@vger.kernel.org, virtualization@lists.linux.dev, David Hildenbrand , Andrew Morton , Oscar Salvador , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Arnd Bergmann , Greg Kroah-Hartman , Jerrin Shaji George , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , Zi Yan Subject: [PATCH v1 07/23] mm/balloon_compaction: use a device-independent balloon (list) lock Date: Tue, 21 Oct 2025 14:59:12 +0200 Message-ID: <20251021125929.377194-8-david@redhat.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251021125929.377194-1-david@redhat.com> References: <20251021125929.377194-1-david@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: hP8-u8IYKJ9mHmRACOuFm_vkY_qUhTEz762_1DmrdZc_1761051588 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspam-User: X-Rspamd-Queue-Id: 16B9C1C000E X-Rspamd-Server: rspam03 X-Stat-Signature: fgadwj8kzq1hy9417yp7t81t18tgpwts X-HE-Tag: 1761051590-206575 X-HE-Meta: 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 lTYcienb 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Signed-off-by: David Hildenbrand --- include/linux/balloon_compaction.h | 6 ++--- mm/balloon_compaction.c | 36 +++++++++++++++++------------- 2 files changed, 23 insertions(+), 19 deletions(-) diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index 3109d3c43d306..e2d9eb40e1fbb 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -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; diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c index fd9ec47cf4670..97e838795354d 100644 --- a/mm/balloon_compaction.c +++ b/mm/balloon_compaction.c @@ -11,6 +11,12 @@ #include #include +/* + * 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; } @@ -230,10 +236,10 @@ 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, @@ -253,7 +259,7 @@ static int balloon_page_migrate(struct page *newpage, struct page *page, rc = b_dev_info->migratepage(b_dev_info, newpage, page, mode); switch (rc) { case 0: - spin_lock_irqsave(&b_dev_info->pages_lock, flags); + spin_lock_irqsave(&balloon_pages_lock, flags); /* Insert the new page into the balloon list. */ get_page(newpage); @@ -272,7 +278,7 @@ static int balloon_page_migrate(struct page *newpage, struct page *page, } break; case -ENOENT: - spin_lock_irqsave(&b_dev_info->pages_lock, flags); + spin_lock_irqsave(&balloon_pages_lock, flags); /* Old page was deflated but new page not inflated. */ __count_vm_event(BALLOON_DEFLATE); @@ -285,7 +291,7 @@ 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); -- 2.51.0