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>
This commit is contained in:
Rafael Aquini
Linus Torvalds
parent
252aa6f5be
commit
18468d93e5
272
include/linux/balloon_compaction.h
Normal file
272
include/linux/balloon_compaction.h
Normal file
@ -0,0 +1,272 @@
|
||||
/*
|
||||
* include/linux/balloon_compaction.h
|
||||
*
|
||||
* Common interface definitions for making balloon pages movable by compaction.
|
||||
*
|
||||
* Despite being perfectly possible to perform ballooned pages migration, they
|
||||
* make a special corner case to compaction scans because balloon pages are not
|
||||
* enlisted at any LRU list like the other pages we do compact / migrate.
|
||||
*
|
||||
* As the page isolation scanning step a compaction thread does is a lockless
|
||||
* procedure (from a page standpoint), it might bring some racy situations while
|
||||
* performing balloon page compaction. In order to sort out these racy scenarios
|
||||
* and safely perform balloon's page compaction and migration we must, always,
|
||||
* ensure following these three simple rules:
|
||||
*
|
||||
* i. when updating a balloon's page ->mapping element, strictly do it under
|
||||
* the following lock order, independently of the far superior
|
||||
* locking scheme (lru_lock, balloon_lock):
|
||||
* +-page_lock(page);
|
||||
* +--spin_lock_irq(&b_dev_info->pages_lock);
|
||||
* ... page->mapping updates here ...
|
||||
*
|
||||
* ii. before isolating or dequeueing a balloon page from the balloon device
|
||||
* pages list, the page reference counter must be raised by one and the
|
||||
* extra refcount must be dropped when the page is enqueued back into
|
||||
* the balloon device page list, thus a balloon page keeps its reference
|
||||
* counter raised only while it is under our special handling;
|
||||
*
|
||||
* iii. after the lockless scan step have selected a potential balloon page for
|
||||
* isolation, re-test the page->mapping flags and the page ref counter
|
||||
* under the proper page lock, to ensure isolating a valid balloon page
|
||||
* (not yet isolated, nor under release procedure)
|
||||
*
|
||||
* 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
|
||||
* set of exposed rules are satisfied while we are dealing with balloon pages
|
||||
* compaction / migration.
|
||||
*
|
||||
* Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
|
||||
*/
|
||||
#ifndef _LINUX_BALLOON_COMPACTION_H
|
||||
#define _LINUX_BALLOON_COMPACTION_H
|
||||
#include <linux/pagemap.h>
|
||||
#include <linux/page-flags.h>
|
||||
#include <linux/migrate.h>
|
||||
#include <linux/gfp.h>
|
||||
#include <linux/err.h>
|
||||
|
||||
/*
|
||||
* Balloon device information descriptor.
|
||||
* This struct is used to allow the common balloon compaction interface
|
||||
* procedures to find the proper balloon device holding memory pages they'll
|
||||
* have to cope for page compaction / migration, as well as it serves the
|
||||
* balloon driver as a page book-keeper for its registered balloon devices.
|
||||
*/
|
||||
struct balloon_dev_info {
|
||||
void *balloon_device; /* balloon device descriptor */
|
||||
struct address_space *mapping; /* balloon special page->mapping */
|
||||
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 */
|
||||
};
|
||||
|
||||
extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
|
||||
extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
|
||||
extern struct balloon_dev_info *balloon_devinfo_alloc(
|
||||
void *balloon_dev_descriptor);
|
||||
|
||||
static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info)
|
||||
{
|
||||
kfree(b_dev_info);
|
||||
}
|
||||
|
||||
/*
|
||||
* balloon_page_free - release a balloon page back to the page free lists
|
||||
* @page: ballooned page to be set free
|
||||
*
|
||||
* This function must be used to properly set free an isolated/dequeued balloon
|
||||
* page at the end of a sucessful page migration, or at the balloon driver's
|
||||
* page release procedure.
|
||||
*/
|
||||
static inline void balloon_page_free(struct page *page)
|
||||
{
|
||||
/*
|
||||
* Balloon pages always get an extra refcount before being isolated
|
||||
* and before being dequeued to help on sorting out fortuite colisions
|
||||
* between a thread attempting to isolate and another thread attempting
|
||||
* to release the very same balloon page.
|
||||
*
|
||||
* Before we handle the page back to Buddy, lets drop its extra refcnt.
|
||||
*/
|
||||
put_page(page);
|
||||
__free_page(page);
|
||||
}
|
||||
|
||||
#ifdef CONFIG_BALLOON_COMPACTION
|
||||
extern bool balloon_page_isolate(struct page *page);
|
||||
extern void balloon_page_putback(struct page *page);
|
||||
extern int balloon_page_migrate(struct page *newpage,
|
||||
struct page *page, enum migrate_mode mode);
|
||||
extern struct address_space
|
||||
*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
|
||||
const struct address_space_operations *a_ops);
|
||||
|
||||
static inline void balloon_mapping_free(struct address_space *balloon_mapping)
|
||||
{
|
||||
kfree(balloon_mapping);
|
||||
}
|
||||
|
||||
/*
|
||||
* page_flags_cleared - helper to perform balloon @page ->flags tests.
|
||||
*
|
||||
* As balloon pages are obtained from buddy and we do not play with page->flags
|
||||
* at driver level (exception made when we get the page lock for compaction),
|
||||
* we can safely identify a ballooned page by checking if the
|
||||
* PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared. This approach also
|
||||
* helps us skip ballooned pages that are locked for compaction or release, thus
|
||||
* mitigating their racy check at balloon_page_movable()
|
||||
*/
|
||||
static inline bool page_flags_cleared(struct page *page)
|
||||
{
|
||||
return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP);
|
||||
}
|
||||
|
||||
/*
|
||||
* __is_movable_balloon_page - helper to perform @page mapping->flags tests
|
||||
*/
|
||||
static inline bool __is_movable_balloon_page(struct page *page)
|
||||
{
|
||||
struct address_space *mapping = page->mapping;
|
||||
return mapping_balloon(mapping);
|
||||
}
|
||||
|
||||
/*
|
||||
* balloon_page_movable - test page->mapping->flags to identify balloon pages
|
||||
* that can be moved by compaction/migration.
|
||||
*
|
||||
* This function is used at core compaction's page isolation scheme, therefore
|
||||
* most pages exposed to it are not enlisted as balloon pages and so, to avoid
|
||||
* undesired side effects like racing against __free_pages(), we cannot afford
|
||||
* holding the page locked while testing page->mapping->flags here.
|
||||
*
|
||||
* As we might return false positives in the case of a balloon page being just
|
||||
* released under us, the page->mapping->flags need to be re-tested later,
|
||||
* under the proper page lock, at the functions that will be coping with the
|
||||
* balloon page case.
|
||||
*/
|
||||
static inline bool balloon_page_movable(struct page *page)
|
||||
{
|
||||
/*
|
||||
* Before dereferencing and testing mapping->flags, let's make sure
|
||||
* this is not a page that uses ->mapping in a different way
|
||||
*/
|
||||
if (page_flags_cleared(page) && !page_mapped(page) &&
|
||||
page_count(page) == 1)
|
||||
return __is_movable_balloon_page(page);
|
||||
|
||||
return false;
|
||||
}
|
||||
|
||||
/*
|
||||
* balloon_page_insert - insert a page into the balloon's page list and make
|
||||
* the page->mapping assignment accordingly.
|
||||
* @page : page to be assigned as a 'balloon page'
|
||||
* @mapping : allocated special 'balloon_mapping'
|
||||
* @head : balloon's device page list head
|
||||
*
|
||||
* Caller must ensure the page is locked and the spin_lock protecting balloon
|
||||
* pages list is held before inserting a page into the balloon device.
|
||||
*/
|
||||
static inline void balloon_page_insert(struct page *page,
|
||||
struct address_space *mapping,
|
||||
struct list_head *head)
|
||||
{
|
||||
page->mapping = mapping;
|
||||
list_add(&page->lru, head);
|
||||
}
|
||||
|
||||
/*
|
||||
* balloon_page_delete - delete a page from balloon's page list and clear
|
||||
* the page->mapping assignement accordingly.
|
||||
* @page : page to be released from balloon's page list
|
||||
*
|
||||
* Caller must ensure the page is locked and the spin_lock protecting balloon
|
||||
* pages list is held before deleting a page from the balloon device.
|
||||
*/
|
||||
static inline void balloon_page_delete(struct page *page)
|
||||
{
|
||||
page->mapping = NULL;
|
||||
list_del(&page->lru);
|
||||
}
|
||||
|
||||
/*
|
||||
* balloon_page_device - get the b_dev_info descriptor for the balloon device
|
||||
* that enqueues the given page.
|
||||
*/
|
||||
static inline struct balloon_dev_info *balloon_page_device(struct page *page)
|
||||
{
|
||||
struct address_space *mapping = page->mapping;
|
||||
if (likely(mapping))
|
||||
return mapping->private_data;
|
||||
|
||||
return NULL;
|
||||
}
|
||||
|
||||
static inline gfp_t balloon_mapping_gfp_mask(void)
|
||||
{
|
||||
return GFP_HIGHUSER_MOVABLE;
|
||||
}
|
||||
|
||||
static inline bool balloon_compaction_check(void)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
#else /* !CONFIG_BALLOON_COMPACTION */
|
||||
|
||||
static inline void *balloon_mapping_alloc(void *balloon_device,
|
||||
const struct address_space_operations *a_ops)
|
||||
{
|
||||
return ERR_PTR(-EOPNOTSUPP);
|
||||
}
|
||||
|
||||
static inline void balloon_mapping_free(struct address_space *balloon_mapping)
|
||||
{
|
||||
return;
|
||||
}
|
||||
|
||||
static inline void balloon_page_insert(struct page *page,
|
||||
struct address_space *mapping,
|
||||
struct list_head *head)
|
||||
{
|
||||
list_add(&page->lru, head);
|
||||
}
|
||||
|
||||
static inline void balloon_page_delete(struct page *page)
|
||||
{
|
||||
list_del(&page->lru);
|
||||
}
|
||||
|
||||
static inline bool balloon_page_movable(struct page *page)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
static inline bool balloon_page_isolate(struct page *page)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
static inline void balloon_page_putback(struct page *page)
|
||||
{
|
||||
return;
|
||||
}
|
||||
|
||||
static inline int balloon_page_migrate(struct page *newpage,
|
||||
struct page *page, enum migrate_mode mode)
|
||||
{
|
||||
return 0;
|
||||
}
|
||||
|
||||
static inline gfp_t balloon_mapping_gfp_mask(void)
|
||||
{
|
||||
return GFP_HIGHUSER;
|
||||
}
|
||||
|
||||
static inline bool balloon_compaction_check(void)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
#endif /* CONFIG_BALLOON_COMPACTION */
|
||||
#endif /* _LINUX_BALLOON_COMPACTION_H */
|
||||
@ -11,8 +11,18 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **);
|
||||
* Return values from addresss_space_operations.migratepage():
|
||||
* - negative errno on page migration failure;
|
||||
* - zero on page migration success;
|
||||
*
|
||||
* The balloon page migration introduces this special case where a 'distinct'
|
||||
* return code is used to flag a successful page migration to unmap_and_move().
|
||||
* This approach is necessary because page migration can race against balloon
|
||||
* deflation procedure, and for such case we could introduce a nasty page leak
|
||||
* if a successfully migrated balloon page gets released concurrently with
|
||||
* migration's unmap_and_move() wrap-up steps.
|
||||
*/
|
||||
#define MIGRATEPAGE_SUCCESS 0
|
||||
#define MIGRATEPAGE_BALLOON_SUCCESS 1 /* special ret code for balloon page
|
||||
* sucessful migration case.
|
||||
*/
|
||||
|
||||
#ifdef CONFIG_MIGRATION
|
||||
|
||||
|
||||
@ -24,6 +24,7 @@ enum mapping_flags {
|
||||
AS_ENOSPC = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
|
||||
AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
|
||||
AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
|
||||
AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */
|
||||
};
|
||||
|
||||
static inline void mapping_set_error(struct address_space *mapping, int error)
|
||||
@ -53,6 +54,21 @@ static inline int mapping_unevictable(struct address_space *mapping)
|
||||
return !!mapping;
|
||||
}
|
||||
|
||||
static inline void mapping_set_balloon(struct address_space *mapping)
|
||||
{
|
||||
set_bit(AS_BALLOON_MAP, &mapping->flags);
|
||||
}
|
||||
|
||||
static inline void mapping_clear_balloon(struct address_space *mapping)
|
||||
{
|
||||
clear_bit(AS_BALLOON_MAP, &mapping->flags);
|
||||
}
|
||||
|
||||
static inline int mapping_balloon(struct address_space *mapping)
|
||||
{
|
||||
return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
|
||||
}
|
||||
|
||||
static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
|
||||
{
|
||||
return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
|
||||
|
||||
15
mm/Kconfig
15
mm/Kconfig
@ -187,6 +187,21 @@ config SPLIT_PTLOCK_CPUS
|
||||
default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
|
||||
default "4"
|
||||
|
||||
#
|
||||
# support for memory balloon compaction
|
||||
config BALLOON_COMPACTION
|
||||
bool "Allow for balloon memory compaction/migration"
|
||||
def_bool y
|
||||
depends on COMPACTION && VIRTIO_BALLOON
|
||||
help
|
||||
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. Allowing the compaction & migration for memory
|
||||
pages enlisted as being part of memory balloon devices avoids the
|
||||
scenario aforementioned and helps improving memory defragmentation.
|
||||
|
||||
#
|
||||
# support for memory compaction
|
||||
config COMPACTION
|
||||
|
||||
@ -16,7 +16,8 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \
|
||||
readahead.o swap.o truncate.o vmscan.o shmem.o \
|
||||
util.o mmzone.o vmstat.o backing-dev.o \
|
||||
mm_init.o mmu_context.o percpu.o slab_common.o \
|
||||
compaction.o interval_tree.o $(mmu-y)
|
||||
compaction.o balloon_compaction.o \
|
||||
interval_tree.o $(mmu-y)
|
||||
|
||||
obj-y += init-mm.o
|
||||
|
||||
|
||||
302
mm/balloon_compaction.c
Normal file
302
mm/balloon_compaction.c
Normal file
@ -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 */
|
||||
Loading…
Reference in New Issue
Block a user