[PATCH 5/8] migrate_pages: batch _unmap and _move

Huang Ying
2022-12-27T00:30:40Z

In this patch the _unmap and _move stage of the folio migration is
batched. That for, previously, it is,

for each folio
_unmap()
_move()

Now, it is,

for each folio
_unmap()
for each folio
_move()

Based on this, we can batch the TLB flushing and use some hardware
accelerator to copy folios between batched _unmap and batched _move
stages.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: haoxin <xhao@linux.alibaba.com>
---
mm/migrate.c | 189 ++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 165 insertions(+), 24 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index e2383b430932..dd68c3de3da8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1027,8 +1027,32 @@ static void __migrate_folio_extract(struct folio *dst,
dst->private = NULL;
}

+static void migrate_folio_undo_src(struct folio *src,
+ int page_was_mapped,
+ struct anon_vma *anon_vma,
+ struct list_head *ret)
+{
+ if (page_was_mapped)
+ remove_migration_ptes(src, src, false);
+ if (anon_vma)
+ put_anon_vma(anon_vma);
+ folio_unlock(src);
+ list_move_tail(&src->lru, ret);
+}
+
+static void migrate_folio_undo_dst(struct folio *dst,
+ free_page_t put_new_page,
+ unsigned long private)
+{
+ folio_unlock(dst);
+ if (put_new_page)
+ put_new_page(&dst->page, private);
+ else
+ folio_put(dst);
+}
+
static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
- int force, enum migrate_mode mode)
+ int force, bool force_lock, enum migrate_mode mode)
{
int rc = -EAGAIN;
int page_was_mapped = 0;
@@ -1055,6 +1079,11 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
if (current->flags & PF_MEMALLOC)
goto out;

+ if (!force_lock) {
+ rc = -EDEADLOCK;
+ goto out;
+ }
+
folio_lock(src);
}

@@ -1168,6 +1197,8 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,

rc = move_to_new_folio(dst, src, mode);

+ if (rc != -EAGAIN)
+ list_del(&dst->lru);
/*
* When successful, push dst to LRU immediately: so that if it
* turns out to be an mlocked page, remove_migration_ptes() will
@@ -1183,6 +1214,11 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,
lru_add_drain();
}

+ if (rc == -EAGAIN) {
+ __migrate_folio_record(dst, page_was_mapped, anon_vma);
+ return rc;
+ }
+
if (page_was_mapped)
remove_migration_ptes(src,
rc == MIGRATEPAGE_SUCCESS ? dst : src, false);
@@ -1223,7 +1259,7 @@ static void migrate_folio_done(struct folio *src,
/* Obtain the lock on page, remove all ptes. */
static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page,
unsigned long private, struct folio *src,
- struct folio **dstp, int force,
+ struct folio **dstp, int force, bool force_lock,
enum migrate_mode mode, enum migrate_reason reason,
struct list_head *ret)
{
@@ -1251,7 +1287,7 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page
*dstp = dst;

dst->private = NULL;
- rc = __migrate_folio_unmap(src, dst, force, mode);
+ rc = __migrate_folio_unmap(src, dst, force, force_lock, mode);
if (rc == MIGRATEPAGE_UNMAP)
return rc;

@@ -1260,7 +1296,7 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page
* references and be restored.
*/
/* restore the folio to right list. */
- if (rc != -EAGAIN)
+ if (rc != -EAGAIN && rc != -EDEADLOCK)
list_move_tail(&src->lru, ret);

if (put_new_page)
@@ -1299,9 +1335,8 @@ static int migrate_folio_move(free_page_t put_new_page, unsigned long private,
*/
if (rc == MIGRATEPAGE_SUCCESS) {
migrate_folio_done(src, reason);
- } else {
- if (rc != -EAGAIN)
- list_add_tail(&src->lru, ret);
+ } else if (rc != -EAGAIN) {
+ list_add_tail(&src->lru, ret);

if (put_new_page)
put_new_page(&dst->page, private);
@@ -1564,7 +1599,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
enum migrate_mode mode, int reason, struct list_head *ret_folios,
struct migrate_pages_stats *stats)
{
- int retry = 1;
+ int retry;
int large_retry = 1;
int thp_retry = 1;
int nr_failed = 0;
@@ -1573,13 +1608,19 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
int pass = 0;
bool is_large = false;
bool is_thp = false;
- struct folio *folio, *folio2, *dst = NULL;
- int rc, nr_pages;
+ struct folio *folio, *folio2, *dst = NULL, *dst2;
+ int rc, rc_saved, nr_pages;
LIST_HEAD(split_folios);
+ LIST_HEAD(unmap_folios);
+ LIST_HEAD(dst_folios);
bool nosplit = (reason == MR_NUMA_MISPLACED);
bool no_split_folio_counting = false;
+ bool force_lock;

-split_folio_migration:
+retry:
+ rc_saved = 0;
+ force_lock = true;
+ retry = 1;
for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
retry = 0;
large_retry = 0;
@@ -1599,16 +1640,15 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
cond_resched();

rc = migrate_folio_unmap(get_new_page, put_new_page, private,
- folio, &dst, pass > 2, mode,
- reason, ret_folios);
- if (rc == MIGRATEPAGE_UNMAP)
- rc = migrate_folio_move(put_new_page, private,
- folio, dst, mode,
- reason, ret_folios);
+ folio, &dst, pass > 2, force_lock,
+ mode, reason, ret_folios);
/*
* The rules are:
* Success: folio will be freed
+ * Unmap: folio will be put on unmap_folios list,
+ * dst folio put on dst_folios list
* -EAGAIN: stay on the from list
+ * -EDEADLOCK: stay on the from list
* -ENOMEM: stay on the from list
* -ENOSYS: stay on the from list
* Other errno: put on ret_folios list
@@ -1643,7 +1683,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
case -ENOMEM:
/*
* When memory is low, don't bother to try to migrate
- * other folios, just exit.
+ * other folios, move unmapped folios, then exit.
*/
if (is_large) {
nr_large_failed++;
@@ -1682,7 +1722,14 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
/* nr_failed isn't updated for not used */
nr_large_failed += large_retry;
stats->nr_thp_failed += thp_retry;
- goto out;
+ rc_saved = rc;
+ if (list_empty(&unmap_folios))
+ goto out;
+ else
+ goto move;
+ case -EDEADLOCK:
+ rc_saved = rc;
+ goto move;
case -EAGAIN:
if (is_large) {
large_retry++;
@@ -1696,6 +1743,15 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
stats->nr_succeeded += nr_pages;
stats->nr_thp_succeeded += is_thp;
break;
+ case MIGRATEPAGE_UNMAP:
+ /*
+ * We have locked some pages, don't force lock
+ * to avoid deadlock.
+ */
+ force_lock = false;
+ list_move_tail(&folio->lru, &unmap_folios);
+ list_add_tail(&dst->lru, &dst_folios);
+ break;
default:
/*
* Permanent failure (-EBUSY, etc.):
@@ -1719,12 +1775,93 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
nr_large_failed += large_retry;
stats->nr_thp_failed += thp_retry;
stats->nr_failed_pages += nr_retry_pages;
+move:
+ retry = 1;
+ for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
+ retry = 0;
+ large_retry = 0;
+ thp_retry = 0;
+ nr_retry_pages = 0;
+
+ dst = list_first_entry(&dst_folios, struct folio, lru);
+ dst2 = list_next_entry(dst, lru);
+ list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) {
+ is_large = folio_test_large(folio);
+ is_thp = is_large && folio_test_pmd_mappable(folio);
+ nr_pages = folio_nr_pages(folio);
+
+ cond_resched();
+
+ rc = migrate_folio_move(put_new_page, private,
+ folio, dst, mode,
+ reason, ret_folios);
+ /*
+ * The rules are:
+ * Success: folio will be freed
+ * -EAGAIN: stay on the unmap_folios list
+ * Other errno: put on ret_folios list
+ */
+ switch(rc) {
+ case -EAGAIN:
+ if (is_large) {
+ large_retry++;
+ thp_retry += is_thp;
+ } else if (!no_split_folio_counting) {
+ retry++;
+ }
+ nr_retry_pages += nr_pages;
+ break;
+ case MIGRATEPAGE_SUCCESS:
+ stats->nr_succeeded += nr_pages;
+ stats->nr_thp_succeeded += is_thp;
+ break;
+ default:
+ if (is_large) {
+ nr_large_failed++;
+ stats->nr_thp_failed += is_thp;
+ } else if (!no_split_folio_counting) {
+ nr_failed++;
+ }
+
+ stats->nr_failed_pages += nr_pages;
+ break;
+ }
+ dst = dst2;
+ dst2 = list_next_entry(dst, lru);
+ }
+ }
+ nr_failed += retry;
+ nr_large_failed += large_retry;
+ stats->nr_thp_failed += thp_retry;
+ stats->nr_failed_pages += nr_retry_pages;
+
+ if (rc_saved)
+ rc = rc_saved;
+ else
+ rc = nr_failed + nr_large_failed;
+out:
+ /* Cleanup remaining folios */
+ dst = list_first_entry(&dst_folios, struct folio, lru);
+ dst2 = list_next_entry(dst, lru);
+ list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) {
+ int page_was_mapped = 0;
+ struct anon_vma *anon_vma = NULL;
+
+ __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
+ migrate_folio_undo_src(folio, page_was_mapped, anon_vma,
+ ret_folios);
+ list_del(&dst->lru);
+ migrate_folio_undo_dst(dst, put_new_page, private);
+ dst = dst2;
+ dst2 = list_next_entry(dst, lru);
+ }
+
/*
* Try to migrate split folios of fail-to-migrate large folios, no
* nr_failed counting in this round, since all split folios of a
* large folio is counted as 1 failure in the first round.
*/
- if (!list_empty(&split_folios)) {
+ if (rc >= 0 && !list_empty(&split_folios)) {
/*
* Move non-migrated folios (after 10 retries) to ret_folios
* to avoid migrating them again.
@@ -1732,12 +1869,16 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
list_splice_init(from, ret_folios);
list_splice_init(&split_folios, from);
no_split_folio_counting = true;
- retry = 1;
- goto split_folio_migration;
+ goto retry;
}

- rc = nr_failed + nr_large_failed;
-out:
+ /*
+ * We have unlocked all locked pages, so we can force lock now, let's
+ * try again.
+ */
+ if (rc == -EDEADLOCK)
+ goto retry;
+
return rc;
}

--
2.35.1