[PATCH 22/34] mm: compaction: Introduce sync-light migration for use by compaction

Mel Gorman
2012-07-23T13:42:57Z

commit a6bc32b899223a877f595ef9ddc1e89ead5072b8 upstream.

Stable note: Not tracked in Buzilla. This was part of a series that
reduced interactivity stalls experienced when THP was enabled.
These stalls were particularly noticable when copying data
to a USB stick but the experiences for users varied a lot.

This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT
mode that avoids writing back pages to backing storage. Async
compaction maps to MIGRATE_ASYNC while sync compaction maps to
MIGRATE_SYNC_LIGHT. For other migrate_pages users such as memory
hotplug, MIGRATE_SYNC is used.

This avoids sync compaction stalling for an excessive length of time,
particularly when copying files to a USB stick where there might be
a large number of dirty pages backed by a filesystem that does not
support ->writepages.

[aarcange@redhat.com: This patch is heavily based on Andrea's work]
[akpm@linux-foundation.org: fix fs/nfs/write.c build]
[akpm@linux-foundation.org: fix fs/btrfs/disk-io.c build]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andy Isaacson <adi@hexapodia.org>
Cc: Nai Xia <nai.xia@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
fs/btrfs/disk-io.c | 3 +-
fs/hugetlbfs/inode.c | 3 +-
fs/nfs/internal.h | 2 +-
fs/nfs/write.c | 2 +-
include/linux/fs.h | 6 ++--
include/linux/migrate.h | 23 +++++++++++---
mm/compaction.c | 2 +-
mm/memory-failure.c | 2 +-
mm/memory_hotplug.c | 2 +-
mm/mempolicy.c | 2 +-
mm/migrate.c | 78 ++++++++++++++++++++++++++---------------------
11 files changed, 75 insertions(+), 50 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 522cb2a..c57d202 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -801,7 +801,8 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,

#ifdef CONFIG_MIGRATION
static int btree_migratepage(struct address_space *mapping,
- struct page *newpage, struct page *page, bool sync)
+ struct page *newpage, struct page *page,
+ enum migrate_mode sync)
{
/*
* we can't safely write a btree page from here,
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 8b0c875..6327a06 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -568,7 +568,8 @@ static int hugetlbfs_set_page_dirty(struct page *page)
}

static int hugetlbfs_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page,
+ enum migrate_mode mode)
{
int rc;

diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index a74442a..4f10d81 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -315,7 +315,7 @@ void nfs_commit_release_pages(struct nfs_write_data *data);

#ifdef CONFIG_MIGRATION
extern int nfs_migrate_page(struct address_space *,
- struct page *, struct page *, bool);
+ struct page *, struct page *, enum migrate_mode);
#else
#define nfs_migrate_page NULL
#endif
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 22a48fd..a5fcc65 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1662,7 +1662,7 @@ out_error:

#ifdef CONFIG_MIGRATION
int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
- struct page *page, bool sync)
+ struct page *page, enum migrate_mode sync)
{
/*
* If PagePrivate is set, then the page is currently associated with
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 09ddec9..212ea7b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -523,6 +523,7 @@ enum positive_aop_returns {
struct page;
struct address_space;
struct writeback_control;
+enum migrate_mode;

struct iov_iter {
const struct iovec *iov;
@@ -612,7 +613,7 @@ struct address_space_operations {
* is false, it must not block.
*/
int (*migratepage) (struct address_space *,
- struct page *, struct page *, bool);
+ struct page *, struct page *, enum migrate_mode);
int (*launder_page) (struct page *);
int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
unsigned long);
@@ -2481,7 +2482,8 @@ extern int generic_check_addressable(unsigned, u64);

#ifdef CONFIG_MIGRATION
extern int buffer_migrate_page(struct address_space *,
- struct page *, struct page *, bool);
+ struct page *, struct page *,
+ enum migrate_mode);
#else
#define buffer_migrate_page NULL
#endif
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 14e6d2a..775787c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -6,18 +6,31 @@

typedef struct page *new_page_t(struct page *, unsigned long private, int **);

+/*
+ * MIGRATE_ASYNC means never block
+ * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
+ * on most operations but not ->writepage as the potential stall time
+ * is too significant
+ * MIGRATE_SYNC will block when migrating pages
+ */
+enum migrate_mode {
+ MIGRATE_ASYNC,
+ MIGRATE_SYNC_LIGHT,
+ MIGRATE_SYNC,
+};
+
#ifdef CONFIG_MIGRATION
#define PAGE_MIGRATION 1

extern void putback_lru_pages(struct list_head *l);
extern int migrate_page(struct address_space *,
- struct page *, struct page *, bool);
+ struct page *, struct page *, enum migrate_mode);
extern int migrate_pages(struct list_head *l, new_page_t x,
unsigned long private, bool offlining,
- bool sync);
+ enum migrate_mode sync);
extern int migrate_huge_pages(struct list_head *l, new_page_t x,
unsigned long private, bool offlining,
- bool sync);
+ enum migrate_mode sync);

extern int fail_migrate_page(struct address_space *,
struct page *, struct page *);
@@ -36,10 +49,10 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
static inline void putback_lru_pages(struct list_head *l) {}
static inline int migrate_pages(struct list_head *l, new_page_t x,
unsigned long private, bool offlining,
- bool sync) { return -ENOSYS; }
+ enum migrate_mode sync) { return -ENOSYS; }
static inline int migrate_huge_pages(struct list_head *l, new_page_t x,
unsigned long private, bool offlining,
- bool sync) { return -ENOSYS; }
+ enum migrate_mode sync) { return -ENOSYS; }

static inline int migrate_prep(void) { return -ENOSYS; }
static inline int migrate_prep_local(void) { return -ENOSYS; }
diff --git a/mm/compaction.c b/mm/compaction.c
index 76bdd65..0d43bb9 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -577,7 +577,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
nr_migrate = cc->nr_migratepages;
err = migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, false,
- cc->sync);
+ cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
update_nr_listpages(cc);
nr_remaining = cc->nr_migratepages;

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 740c4f5..6496748 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1464,7 +1464,7 @@ int soft_offline_page(struct page *page, int flags)
page_is_file_cache(page));
list_add(&page->lru, &pagelist);
ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
- 0, true);
+ 0, MIGRATE_SYNC);
if (ret) {
putback_lru_pages(&pagelist);
pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c46887b..ae5a3f2 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -747,7 +747,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
}
/* this function returns # of failed pages */
ret = migrate_pages(&source, hotremove_migrate_alloc, 0,
- true, true);
+ true, MIGRATE_SYNC);
if (ret)
putback_lru_pages(&source);
}
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3dac2d1..dd5f874 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -926,7 +926,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,

if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, new_node_page, dest,
- false, true);
+ false, MIGRATE_SYNC);
if (err)
putback_lru_pages(&pagelist);
}
diff --git a/mm/migrate.c b/mm/migrate.c
index fb8d1ae..132063e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -222,12 +222,13 @@ out:

#ifdef CONFIG_BLOCK
/* Returns true if all buffers are successfully locked */
-static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
+static bool buffer_migrate_lock_buffers(struct buffer_head *head,
+ enum migrate_mode mode)
{
struct buffer_head *bh = head;

/* Simple case, sync compaction */
- if (sync) {
+ if (mode != MIGRATE_ASYNC) {
do {
get_bh(bh);
lock_buffer(bh);
@@ -263,7 +264,7 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
}
#else
static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
- bool sync)
+ enum migrate_mode mode)
{
return true;
}
@@ -279,7 +280,7 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
*/
static int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
- struct buffer_head *head, bool sync)
+ struct buffer_head *head, enum migrate_mode mode)
{
int expected_count;
void **pslot;
@@ -315,7 +316,8 @@ static int migrate_page_move_mapping(struct address_space *mapping,
* the mapping back due to an elevated page count, we would have to
* block waiting on other references to be dropped.
*/
- if (!sync && head && !buffer_migrate_lock_buffers(head, sync)) {
+ if (mode == MIGRATE_ASYNC && head &&
+ !buffer_migrate_lock_buffers(head, mode)) {
page_unfreeze_refs(page, expected_count);
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
@@ -478,13 +480,14 @@ EXPORT_SYMBOL(fail_migrate_page);
* Pages are locked upon entry and exit.
*/
int migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page, bool sync)
+ struct page *newpage, struct page *page,
+ enum migrate_mode mode)
{
int rc;

BUG_ON(PageWriteback(page)); /* Writeback must be complete */

- rc = migrate_page_move_mapping(mapping, newpage, page, NULL, sync);
+ rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);

if (rc)
return rc;
@@ -501,17 +504,17 @@ EXPORT_SYMBOL(migrate_page);
* exist.
*/
int buffer_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page, bool sync)
+ struct page *newpage, struct page *page, enum migrate_mode mode)
{
struct buffer_head *bh, *head;
int rc;

if (!page_has_buffers(page))
- return migrate_page(mapping, newpage, page, sync);
+ return migrate_page(mapping, newpage, page, mode);

head = page_buffers(page);

- rc = migrate_page_move_mapping(mapping, newpage, page, head, sync);
+ rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);

if (rc)
return rc;
@@ -521,8 +524,8 @@ int buffer_migrate_page(struct address_space *mapping,
* with an IRQ-safe spinlock held. In the sync case, the buffers
* need to be locked no
*/
- if (sync)
- BUG_ON(!buffer_migrate_lock_buffers(head, sync));
+ if (mode != MIGRATE_ASYNC)
+ BUG_ON(!buffer_migrate_lock_buffers(head, mode));

ClearPagePrivate(page);
set_page_private(newpage, page_private(page));
@@ -599,10 +602,11 @@ static int writeout(struct address_space *mapping, struct page *page)
* Default handling if a filesystem does not provide a migration function.
*/
static int fallback_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page, bool sync)
+ struct page *newpage, struct page *page, enum migrate_mode mode)
{
if (PageDirty(page)) {
- if (!sync)
+ /* Only writeback pages in full synchronous migration */
+ if (mode != MIGRATE_SYNC)
return -EBUSY;
return writeout(mapping, page);
}
@@ -615,7 +619,7 @@ static int fallback_migrate_page(struct address_space *mapping,
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;

- return migrate_page(mapping, newpage, page, sync);
+ return migrate_page(mapping, newpage, page, mode);
}

/*
@@ -630,7 +634,7 @@ static int fallback_migrate_page(struct address_space *mapping,
* == 0 - success
*/
static int move_to_new_page(struct page *newpage, struct page *page,
- int remap_swapcache, bool sync)
+ int remap_swapcache, enum migrate_mode mode)
{
struct address_space *mapping;
int rc;
@@ -651,7 +655,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,

mapping = page_mapping(page);
if (!mapping)
- rc = migrate_page(mapping, newpage, page, sync);
+ rc = migrate_page(mapping, newpage, page, mode);
else if (mapping->a_ops->migratepage)
/*
* Most pages have a mapping and most filesystems provide a
@@ -660,9 +664,9 @@ static int move_to_new_page(struct page *newpage, struct page *page,
* is the most common path for page migration.
*/
rc = mapping->a_ops->migratepage(mapping,
- newpage, page, sync);
+ newpage, page, mode);
else
- rc = fallback_migrate_page(mapping, newpage, page, sync);
+ rc = fallback_migrate_page(mapping, newpage, page, mode);

if (rc) {
newpage->mapping = NULL;
@@ -677,7 +681,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
}

static int __unmap_and_move(struct page *page, struct page *newpage,
- int force, bool offlining, bool sync)
+ int force, bool offlining, enum migrate_mode mode)
{
int rc = -EAGAIN;
int remap_swapcache = 1;
@@ -686,7 +690,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
struct anon_vma *anon_vma = NULL;

if (!trylock_page(page)) {
- if (!force || !sync)
+ if (!force || mode == MIGRATE_ASYNC)
goto out;

/*
@@ -732,10 +736,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage,

if (PageWriteback(page)) {
/*
- * For !sync, there is no point retrying as the retry loop
- * is expected to be too short for PageWriteback to be cleared
+ * Only in the case of a full syncronous migration is it
+ * necessary to wait for PageWriteback. In the async case,
+ * the retry loop is too short and in the sync-light case,
+ * the overhead of stalling is too much
*/
- if (!sync) {
+ if (mode != MIGRATE_SYNC) {
rc = -EBUSY;
goto uncharge;
}
@@ -806,7 +812,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,

skip_unmap:
if (!page_mapped(page))
- rc = move_to_new_page(newpage, page, remap_swapcache, sync);
+ rc = move_to_new_page(newpage, page, remap_swapcache, mode);

if (rc && remap_swapcache)
remove_migration_ptes(page, page);
@@ -829,7 +835,8 @@ out:
* to the newly allocated page in newpage.
*/
static int unmap_and_move(new_page_t get_new_page, unsigned long private,
- struct page *page, int force, bool offlining, bool sync)
+ struct page *page, int force, bool offlining,
+ enum migrate_mode mode)
{
int rc = 0;
int *result = NULL;
@@ -847,7 +854,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
if (unlikely(split_huge_page(page)))
goto out;

- rc = __unmap_and_move(page, newpage, force, offlining, sync);
+ rc = __unmap_and_move(page, newpage, force, offlining, mode);
out:
if (rc != -EAGAIN) {
/*
@@ -897,7 +904,8 @@ out:
*/
static int unmap_and_move_huge_page(new_page_t get_new_page,
unsigned long private, struct page *hpage,
- int force, bool offlining, bool sync)
+ int force, bool offlining,
+ enum migrate_mode mode)
{
int rc = 0;
int *result = NULL;
@@ -910,7 +918,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
rc = -EAGAIN;

if (!trylock_page(hpage)) {
- if (!force || !sync)
+ if (!force || mode != MIGRATE_SYNC)
goto out;
lock_page(hpage);
}
@@ -921,7 +929,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

if (!page_mapped(hpage))
- rc = move_to_new_page(new_hpage, hpage, 1, sync);
+ rc = move_to_new_page(new_hpage, hpage, 1, mode);

if (rc)
remove_migration_ptes(hpage, hpage);
@@ -964,7 +972,7 @@ out:
*/
int migrate_pages(struct list_head *from,
new_page_t get_new_page, unsigned long private, bool offlining,
- bool sync)
+ enum migrate_mode mode)
{
int retry = 1;
int nr_failed = 0;
@@ -985,7 +993,7 @@ int migrate_pages(struct list_head *from,

rc = unmap_and_move(get_new_page, private,
page, pass > 2, offlining,
- sync);
+ mode);

switch(rc) {
case -ENOMEM:
@@ -1015,7 +1023,7 @@ out:

int migrate_huge_pages(struct list_head *from,
new_page_t get_new_page, unsigned long private, bool offlining,
- bool sync)
+ enum migrate_mode mode)
{
int retry = 1;
int nr_failed = 0;
@@ -1032,7 +1040,7 @@ int migrate_huge_pages(struct list_head *from,

rc = unmap_and_move_huge_page(get_new_page,
private, page, pass > 2, offlining,
- sync);
+ mode);

switch(rc) {
case -ENOMEM:
@@ -1161,7 +1169,7 @@ set_status:
err = 0;
if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, new_page_node,
- (unsigned long)pm, 0, true);
+ (unsigned long)pm, 0, MIGRATE_SYNC);
if (err)
putback_lru_pages(&pagelist);
}
--
1.7.9.2