mm: introduce a common interface for balloon pages mobility

Memory fragmentation introduced by ballooning might reduce significantly
the number of 2MB contiguous memory blocks that can be used within a guest,
thus imposing performance penalties associated with the reduced number of
transparent huge pages that could be used by the guest workload.

This patch introduces a common interface to help a balloon driver on
making its page set movable to compaction, and thus allowing the system
to better leverage the compation efforts on memory defragmentation.

[akpm@linux-foundation.org: use PAGE_FLAGS_CHECK_AT_PREP, s/__balloon_page_flags/page_flags_cleared/, small cleanups]
[rientjes@google.com: allow balloon compaction for any system with memory compaction enabled, which is the defconfig]
Signed-off-by: Rafael Aquini <aquini@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 302 insertions, 0 deletions

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
new file mode 100644
index 000000000000..07dbc8ec46cf
--- /dev/null
+++ b/mm/balloon_compaction.c
@@ -0,0 +1,302 @@
+/*
+ * 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>
+
+/*
+ * balloon_devinfo_alloc - allocates a balloon device information descriptor.
+ * @balloon_dev_descriptor: pointer to reference the balloon device which
+ *                          this struct balloon_dev_info will be servicing.
+ *
+ * Driver must call it to properly allocate and initialize an instance of
+ * struct balloon_dev_info which will be used to reference a balloon device
+ * as well as to keep track of the balloon device page list.
+ */
+struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
+{
+        struct balloon_dev_info *b_dev_info;
+        b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
+        if (!b_dev_info)
+                return ERR_PTR(-ENOMEM);
+
+        b_dev_info->balloon_device = balloon_dev_descriptor;
+        b_dev_info->mapping = NULL;
+        b_dev_info->isolated_pages = 0;
+        spin_lock_init(&b_dev_info->pages_lock);
+        INIT_LIST_HEAD(&b_dev_info->pages);
+
+        return b_dev_info;
+}
+EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
+
+/*
+ * balloon_page_enqueue - allocates a new page and inserts it into the balloon
+ *                        page list.
+ * @b_dev_info: balloon device decriptor where we will insert a new page to
+ *
+ * Driver must call it to properly allocate a new enlisted balloon page
+ * before definetively removing it from the guest system.
+ * This function returns the page address for the recently enqueued page or
+ * NULL in the case we fail to allocate a new page this turn.
+ */
+struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
+{
+        unsigned long flags;
+        struct page *page = alloc_page(balloon_mapping_gfp_mask() |
+                                        __GFP_NOMEMALLOC | __GFP_NORETRY);
+        if (!page)
+                return NULL;
+
+        /*
+         * 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.
+         */
+        BUG_ON(!trylock_page(page));
+        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+        balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
+        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+        unlock_page(page);
+        return page;
+}
+EXPORT_SYMBOL_GPL(balloon_page_enqueue);
+
+/*
+ * balloon_page_dequeue - removes a page from balloon's page list and returns
+ *                        the its address to allow the driver release the page.
+ * @b_dev_info: balloon device decriptor where we will grab a page from.
+ *
+ * Driver must call it to properly de-allocate a previous enlisted balloon page
+ * before definetively releasing it back to the guest system.
+ * This function returns the page address for the recently dequeued page or
+ * NULL in the case we find balloon's page list temporarily empty due to
+ * compaction isolated pages.
+ */
+struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
+{
+        struct page *page, *tmp;
+        unsigned long flags;
+        bool dequeued_page;
+
+        dequeued_page = false;
+        list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
+                /*
+                 * Block others from accessing the 'page' while we get around
+                 * establishing additional references and preparing the 'page'
+                 * to be released by the balloon driver.
+                 */
+                if (trylock_page(page)) {
+                        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+                        /*
+                         * Raise the page refcount here to prevent any wrong
+                         * attempt to isolate this page, in case of coliding
+                         * with balloon_page_isolate() just after we release
+                         * the page lock.
+                         *
+                         * balloon_page_free() will take care of dropping
+                         * this extra refcount later.
+                         */
+                        get_page(page);
+                        balloon_page_delete(page);
+                        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+                        unlock_page(page);
+                        dequeued_page = true;
+                        break;
+                }
+        }
+
+        if (!dequeued_page) {
+                /*
+                 * If we are unable to dequeue a balloon page because the page
+                 * list is empty and there is no isolated pages, then something
+                 * went out of track and some balloon pages are lost.
+                 * BUG() here, otherwise the balloon driver may get stuck into
+                 * 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);
+                page = NULL;
+        }
+        return page;
+}
+EXPORT_SYMBOL_GPL(balloon_page_dequeue);
+
+#ifdef CONFIG_BALLOON_COMPACTION
+/*
+ * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
+ * @b_dev_info: holds the balloon device information descriptor.
+ * @a_ops: balloon_mapping address_space_operations descriptor.
+ *
+ * Driver must call it to properly allocate and initialize an instance of
+ * struct address_space which will be used as the special page->mapping for
+ * balloon device enlisted page instances.
+ */
+struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
+                                const struct address_space_operations *a_ops)
+{
+        struct address_space *mapping;
+
+        mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
+        if (!mapping)
+                return ERR_PTR(-ENOMEM);
+
+        /*
+         * Give a clean 'zeroed' status to all elements of this special
+         * balloon page->mapping struct address_space instance.
+         */
+        address_space_init_once(mapping);
+
+        /*
+         * Set mapping->flags appropriately, to allow balloon pages
+         * ->mapping identification.
+         */
+        mapping_set_balloon(mapping);
+        mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
+
+        /* balloon's page->mapping->a_ops callback descriptor */
+        mapping->a_ops = a_ops;
+
+        /*
+         * Establish a pointer reference back to the balloon device descriptor
+         * this particular page->mapping will be servicing.
+         * This is used by compaction / migration procedures to identify and
+         * access the balloon device pageset while isolating / migrating pages.
+         *
+         * As some balloon drivers can register multiple balloon devices
+         * for a single guest, this also helps compaction / migration to
+         * properly deal with multiple balloon pagesets, when required.
+         */
+        mapping->private_data = b_dev_info;
+        b_dev_info->mapping = mapping;
+
+        return mapping;
+}
+EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
+
+static inline void __isolate_balloon_page(struct page *page)
+{
+        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        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);
+}
+
+static inline void __putback_balloon_page(struct page *page)
+{
+        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        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);
+}
+
+static inline int __migrate_balloon_page(struct address_space *mapping,
+                struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+        return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
+}
+
+/* __isolate_lru_page() counterpart for a ballooned page */
+bool balloon_page_isolate(struct page *page)
+{
+        /*
+         * Avoid burning cycles with pages that are yet under __free_pages(),
+         * or just got freed under us.
+         *
+         * In case we 'win' a race for a balloon page being freed under us and
+         * raise its refcount preventing __free_pages() from doing its job
+         * the put_page() at the end of this block will take care of
+         * release this page, thus avoiding a nasty leakage.
+         */
+        if (likely(get_page_unless_zero(page))) {
+                /*
+                 * As balloon pages are not isolated from LRU lists, concurrent
+                 * compaction threads can race against page migration functions
+                 * as well as race against the balloon driver releasing a page.
+                 *
+                 * In order to avoid having an already isolated balloon page
+                 * being (wrongly) re-isolated while it is under migration,
+                 * or to avoid attempting to isolate pages being released by
+                 * the balloon driver, lets be sure we have the page lock
+                 * before proceeding with the balloon page isolation steps.
+                 */
+                if (likely(trylock_page(page))) {
+                        /*
+                         * A ballooned page, by default, has just one refcount.
+                         * Prevent concurrent compaction threads from isolating
+                         * an already isolated balloon page by refcount check.
+                         */
+                        if (__is_movable_balloon_page(page) &&
+                            page_count(page) == 2) {
+                                __isolate_balloon_page(page);
+                                unlock_page(page);
+                                return true;
+                        }
+                        unlock_page(page);
+                }
+                put_page(page);
+        }
+        return false;
+}
+
+/* putback_lru_page() counterpart for a ballooned page */
+void balloon_page_putback(struct page *page)
+{
+        /*
+         * 'lock_page()' stabilizes the page and prevents races against
+         * concurrent isolation threads attempting to re-isolate it.
+         */
+        lock_page(page);
+
+        if (__is_movable_balloon_page(page)) {
+                __putback_balloon_page(page);
+                /* drop the extra ref count taken for page isolation */
+                put_page(page);
+        } else {
+                WARN_ON(1);
+                dump_page(page);
+        }
+        unlock_page(page);
+}
+
+/* move_to_new_page() counterpart for a ballooned page */
+int balloon_page_migrate(struct page *newpage,
+                         struct page *page, enum migrate_mode mode)
+{
+        struct address_space *mapping;
+        int rc = -EAGAIN;
+
+        /*
+         * Block others from accessing the 'newpage' when we get around to
+         * establishing additional references. We should be the only one
+         * holding a reference to the 'newpage' at this point.
+         */
+        BUG_ON(!trylock_page(newpage));
+
+        if (WARN_ON(!__is_movable_balloon_page(page))) {
+                dump_page(page);
+                unlock_page(newpage);
+                return rc;
+        }
+
+        mapping = page->mapping;
+        if (mapping)
+                rc = __migrate_balloon_page(mapping, newpage, page, mode);
+
+        unlock_page(newpage);
+        return rc;
+}
+#endif /* CONFIG_BALLOON_COMPACTION */