Commit 18468d93 authored by Rafael Aquini's avatar Rafael Aquini Committed by Linus Torvalds

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: default avatarRafael Aquini <aquini@redhat.com>
Acked-by: default avatarMel 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: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 252aa6f5
/*
* 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;
......
......@@ -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
......
/*
* 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 */
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