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>
Šī revīzija ir iekļauta:
Rafael Aquini
revīziju iesūtīja
Linus Torvalds
Linus Torvalds
vecāks
252aa6f5be
revīzija
18468d93e5
302
mm/balloon_compaction.c
Parasts fails
302
mm/balloon_compaction.c
Parasts fails
@@ -0,0 +1,302 @@
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/*
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* mm/balloon_compaction.c
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*
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* Common interface for making balloon pages movable by compaction.
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*
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* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
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*/
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#include <linux/mm.h>
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#include <linux/slab.h>
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#include <linux/export.h>
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#include <linux/balloon_compaction.h>
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/*
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* balloon_devinfo_alloc - allocates a balloon device information descriptor.
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* @balloon_dev_descriptor: pointer to reference the balloon device which
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* this struct balloon_dev_info will be servicing.
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*
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* Driver must call it to properly allocate and initialize an instance of
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* struct balloon_dev_info which will be used to reference a balloon device
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* as well as to keep track of the balloon device page list.
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*/
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struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
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{
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struct balloon_dev_info *b_dev_info;
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b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
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if (!b_dev_info)
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return ERR_PTR(-ENOMEM);
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b_dev_info->balloon_device = balloon_dev_descriptor;
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b_dev_info->mapping = NULL;
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b_dev_info->isolated_pages = 0;
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spin_lock_init(&b_dev_info->pages_lock);
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INIT_LIST_HEAD(&b_dev_info->pages);
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return b_dev_info;
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}
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EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
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/*
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* balloon_page_enqueue - allocates a new page and inserts it into the balloon
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* page list.
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* @b_dev_info: balloon device decriptor where we will insert a new page to
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*
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* Driver must call it to properly allocate a new enlisted balloon page
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* before definetively removing it from the guest system.
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* This function returns the page address for the recently enqueued page or
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* NULL in the case we fail to allocate a new page this turn.
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*/
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struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
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{
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unsigned long flags;
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struct page *page = alloc_page(balloon_mapping_gfp_mask() |
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__GFP_NOMEMALLOC | __GFP_NORETRY);
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if (!page)
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return NULL;
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/*
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* Block others from accessing the 'page' when we get around to
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* establishing additional references. We should be the only one
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* holding a reference to the 'page' at this point.
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*/
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BUG_ON(!trylock_page(page));
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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unlock_page(page);
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return page;
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}
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EXPORT_SYMBOL_GPL(balloon_page_enqueue);
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/*
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* balloon_page_dequeue - removes a page from balloon's page list and returns
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* the its address to allow the driver release the page.
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* @b_dev_info: balloon device decriptor where we will grab a page from.
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*
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* Driver must call it to properly de-allocate a previous enlisted balloon page
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* before definetively releasing it back to the guest system.
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* This function returns the page address for the recently dequeued page or
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* NULL in the case we find balloon's page list temporarily empty due to
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* compaction isolated pages.
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*/
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struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
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{
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struct page *page, *tmp;
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unsigned long flags;
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bool dequeued_page;
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dequeued_page = false;
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list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
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/*
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* Block others from accessing the 'page' while we get around
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* establishing additional references and preparing the 'page'
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* to be released by the balloon driver.
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*/
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if (trylock_page(page)) {
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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/*
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* Raise the page refcount here to prevent any wrong
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* attempt to isolate this page, in case of coliding
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* with balloon_page_isolate() just after we release
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* the page lock.
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*
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* balloon_page_free() will take care of dropping
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* this extra refcount later.
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*/
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get_page(page);
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balloon_page_delete(page);
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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unlock_page(page);
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dequeued_page = true;
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break;
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}
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}
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if (!dequeued_page) {
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/*
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* If we are unable to dequeue a balloon page because the page
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* list is empty and there is no isolated pages, then something
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* went out of track and some balloon pages are lost.
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* BUG() here, otherwise the balloon driver may get stuck into
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* an infinite loop while attempting to release all its pages.
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*/
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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if (unlikely(list_empty(&b_dev_info->pages) &&
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!b_dev_info->isolated_pages))
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BUG();
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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page = NULL;
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}
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return page;
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}
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EXPORT_SYMBOL_GPL(balloon_page_dequeue);
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#ifdef CONFIG_BALLOON_COMPACTION
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/*
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* balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
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* @b_dev_info: holds the balloon device information descriptor.
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* @a_ops: balloon_mapping address_space_operations descriptor.
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*
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* Driver must call it to properly allocate and initialize an instance of
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* struct address_space which will be used as the special page->mapping for
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* balloon device enlisted page instances.
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*/
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struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
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const struct address_space_operations *a_ops)
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{
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struct address_space *mapping;
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mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
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if (!mapping)
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return ERR_PTR(-ENOMEM);
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/*
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* Give a clean 'zeroed' status to all elements of this special
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* balloon page->mapping struct address_space instance.
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*/
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address_space_init_once(mapping);
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/*
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* Set mapping->flags appropriately, to allow balloon pages
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* ->mapping identification.
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*/
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mapping_set_balloon(mapping);
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mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
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/* balloon's page->mapping->a_ops callback descriptor */
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mapping->a_ops = a_ops;
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/*
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* Establish a pointer reference back to the balloon device descriptor
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* this particular page->mapping will be servicing.
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* This is used by compaction / migration procedures to identify and
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* access the balloon device pageset while isolating / migrating pages.
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*
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* As some balloon drivers can register multiple balloon devices
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* for a single guest, this also helps compaction / migration to
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* properly deal with multiple balloon pagesets, when required.
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*/
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mapping->private_data = b_dev_info;
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b_dev_info->mapping = mapping;
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return mapping;
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}
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EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
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static inline void __isolate_balloon_page(struct page *page)
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{
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struct balloon_dev_info *b_dev_info = page->mapping->private_data;
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unsigned long flags;
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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list_del(&page->lru);
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b_dev_info->isolated_pages++;
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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}
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static inline void __putback_balloon_page(struct page *page)
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{
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struct balloon_dev_info *b_dev_info = page->mapping->private_data;
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unsigned long flags;
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spin_lock_irqsave(&b_dev_info->pages_lock, flags);
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list_add(&page->lru, &b_dev_info->pages);
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b_dev_info->isolated_pages--;
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spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
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}
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static inline int __migrate_balloon_page(struct address_space *mapping,
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struct page *newpage, struct page *page, enum migrate_mode mode)
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{
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return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
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}
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/* __isolate_lru_page() counterpart for a ballooned page */
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bool balloon_page_isolate(struct page *page)
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{
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/*
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* Avoid burning cycles with pages that are yet under __free_pages(),
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* or just got freed under us.
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*
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* In case we 'win' a race for a balloon page being freed under us and
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* raise its refcount preventing __free_pages() from doing its job
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* the put_page() at the end of this block will take care of
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* release this page, thus avoiding a nasty leakage.
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*/
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if (likely(get_page_unless_zero(page))) {
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/*
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* As balloon pages are not isolated from LRU lists, concurrent
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* compaction threads can race against page migration functions
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* as well as race against the balloon driver releasing a page.
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*
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* In order to avoid having an already isolated balloon page
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* being (wrongly) re-isolated while it is under migration,
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* or to avoid attempting to isolate pages being released by
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* the balloon driver, lets be sure we have the page lock
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* before proceeding with the balloon page isolation steps.
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*/
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if (likely(trylock_page(page))) {
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/*
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* A ballooned page, by default, has just one refcount.
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* Prevent concurrent compaction threads from isolating
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* an already isolated balloon page by refcount check.
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*/
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if (__is_movable_balloon_page(page) &&
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page_count(page) == 2) {
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__isolate_balloon_page(page);
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unlock_page(page);
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return true;
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}
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unlock_page(page);
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}
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put_page(page);
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}
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return false;
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}
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/* putback_lru_page() counterpart for a ballooned page */
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void balloon_page_putback(struct page *page)
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{
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/*
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* 'lock_page()' stabilizes the page and prevents races against
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* concurrent isolation threads attempting to re-isolate it.
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*/
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lock_page(page);
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if (__is_movable_balloon_page(page)) {
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__putback_balloon_page(page);
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/* drop the extra ref count taken for page isolation */
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put_page(page);
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} else {
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WARN_ON(1);
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dump_page(page);
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}
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unlock_page(page);
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}
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/* move_to_new_page() counterpart for a ballooned page */
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int balloon_page_migrate(struct page *newpage,
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struct page *page, enum migrate_mode mode)
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{
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struct address_space *mapping;
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int rc = -EAGAIN;
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/*
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* Block others from accessing the 'newpage' when we get around to
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* establishing additional references. We should be the only one
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* holding a reference to the 'newpage' at this point.
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*/
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BUG_ON(!trylock_page(newpage));
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if (WARN_ON(!__is_movable_balloon_page(page))) {
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dump_page(page);
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unlock_page(newpage);
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return rc;
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}
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mapping = page->mapping;
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if (mapping)
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rc = __migrate_balloon_page(mapping, newpage, page, mode);
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unlock_page(newpage);
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return rc;
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}
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#endif /* CONFIG_BALLOON_COMPACTION */
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