[RFC 2/6] mm/migrate_pages: split unmap_and_move() to _unmap() and _move()

Huang Ying
2022-09-21T06:07:09Z

This is a preparation patch to batch the page unmapping and moving
for the normal pages and THP.

In this patch, unmap_and_move() is split to migrate_page_unmap() and
migrate_page_move(). So, we can batch _unmap() and _move() in
different loops later. To pass some information between unmap and
move, the original unused newpage->mapping and newpage->private are
used.

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>
---
mm/migrate.c | 164 ++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 122 insertions(+), 42 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 117134f1c6dc..4a81e0bfdbcd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -976,13 +976,32 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
return rc;
}

-static int __unmap_and_move(struct page *page, struct page *newpage,
+static void __migrate_page_record(struct page *newpage,
+ int page_was_mapped,
+ struct anon_vma *anon_vma)
+{
+ newpage->mapping = (struct address_space *)anon_vma;
+ newpage->private = page_was_mapped;
+}
+
+static void __migrate_page_extract(struct page *newpage,
+ int *page_was_mappedp,
+ struct anon_vma **anon_vmap)
+{
+ *anon_vmap = (struct anon_vma *)newpage->mapping;
+ *page_was_mappedp = newpage->private;
+ newpage->mapping = NULL;
+ newpage->private = 0;
+}
+
+#define MIGRATEPAGE_UNMAP 1
+
+static int __migrate_page_unmap(struct page *page, struct page *newpage,
int force, enum migrate_mode mode)
{
struct folio *folio = page_folio(page);
- struct folio *dst = page_folio(newpage);
int rc = -EAGAIN;
- bool page_was_mapped = false;
+ int page_was_mapped = 0;
struct anon_vma *anon_vma = NULL;
bool is_lru = !__PageMovable(page);

@@ -1058,8 +1077,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
goto out_unlock;

if (unlikely(!is_lru)) {
- rc = move_to_new_folio(dst, folio, mode);
- goto out_unlock_both;
+ __migrate_page_record(newpage, page_was_mapped, anon_vma);
+ return MIGRATEPAGE_UNMAP;
}

/*
@@ -1085,11 +1104,41 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
page);
try_to_migrate(folio, 0);
- page_was_mapped = true;
+ page_was_mapped = 1;
+ }
+
+ if (!page_mapped(page)) {
+ __migrate_page_record(newpage, page_was_mapped, anon_vma);
+ return MIGRATEPAGE_UNMAP;
}

- if (!page_mapped(page))
- rc = move_to_new_folio(dst, folio, mode);
+ if (page_was_mapped)
+ remove_migration_ptes(folio, folio, false);
+
+out_unlock_both:
+ unlock_page(newpage);
+out_unlock:
+ /* Drop an anon_vma reference if we took one */
+ if (anon_vma)
+ put_anon_vma(anon_vma);
+ unlock_page(page);
+out:
+
+ return rc;
+}
+
+static int __migrate_page_move(struct page *page, struct page *newpage,
+ enum migrate_mode mode)
+{
+ struct folio *folio = page_folio(page);
+ struct folio *dst = page_folio(newpage);
+ int rc;
+ int page_was_mapped = 0;
+ struct anon_vma *anon_vma = NULL;
+
+ __migrate_page_extract(newpage, &page_was_mapped, &anon_vma);
+
+ rc = move_to_new_folio(dst, folio, mode);

/*
* When successful, push newpage to LRU immediately: so that if it
@@ -1110,14 +1159,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
remove_migration_ptes(folio,
rc == MIGRATEPAGE_SUCCESS ? dst : folio, false);

-out_unlock_both:
unlock_page(newpage);
-out_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);
unlock_page(page);
-out:
/*
* If migration is successful, decrease refcount of the newpage,
* which will not free the page because new page owner increased
@@ -1129,18 +1175,31 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
return rc;
}

-/*
- * Obtain the lock on page, remove all ptes and migrate the page
- * to the newly allocated page in newpage.
- */
-static int unmap_and_move(new_page_t get_new_page,
- free_page_t put_new_page,
- unsigned long private, struct page *page,
- int force, enum migrate_mode mode,
- enum migrate_reason reason,
- struct list_head *ret)
+static void migrate_page_done(struct page *page,
+ enum migrate_reason reason)
+{
+ /*
+ * Compaction can migrate also non-LRU pages which are
+ * not accounted to NR_ISOLATED_*. They can be recognized
+ * as __PageMovable
+ */
+ if (likely(!__PageMovable(page)))
+ mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
+ page_is_file_lru(page), -thp_nr_pages(page));
+
+ if (reason != MR_MEMORY_FAILURE)
+ /* We release the page in page_handle_poison. */
+ put_page(page);
+}
+
+/* Obtain the lock on page, remove all ptes. */
+static int migrate_page_unmap(new_page_t get_new_page, free_page_t put_new_page,
+ unsigned long private, struct page *page,
+ struct page **newpagep, int force,
+ enum migrate_mode mode, enum migrate_reason reason,
+ struct list_head *ret)
{
- int rc = MIGRATEPAGE_SUCCESS;
+ int rc = MIGRATEPAGE_UNMAP;
struct page *newpage = NULL;

if (!thp_migration_supported() && PageTransHuge(page))
@@ -1151,19 +1210,48 @@ static int unmap_and_move(new_page_t get_new_page,
ClearPageActive(page);
ClearPageUnevictable(page);
/* free_pages_prepare() will clear PG_isolated. */
- goto out;
+ list_del(&page->lru);
+ migrate_page_done(page, reason);
+ return MIGRATEPAGE_SUCCESS;
}

newpage = get_new_page(page, private);
if (!newpage)
return -ENOMEM;
+ *newpagep = newpage;

- newpage->private = 0;
- rc = __unmap_and_move(page, newpage, force, mode);
+ rc = __migrate_page_unmap(page, newpage, force, mode);
+ if (rc == MIGRATEPAGE_UNMAP)
+ return rc;
+
+ /*
+ * A page that has not been migrated will have kept its
+ * references and be restored.
+ */
+ /* restore the page to right list. */
+ if (rc != -EAGAIN)
+ list_move_tail(&page->lru, ret);
+
+ if (put_new_page)
+ put_new_page(newpage, private);
+ else
+ put_page(newpage);
+
+ return rc;
+}
+
+/* Migrate the page to the newly allocated page in newpage. */
+static int migrate_page_move(free_page_t put_new_page, unsigned long private,
+ struct page *page, struct page *newpage,
+ enum migrate_mode mode, enum migrate_reason reason,
+ struct list_head *ret)
+{
+ int rc;
+
+ rc = __migrate_page_move(page, newpage, mode);
if (rc == MIGRATEPAGE_SUCCESS)
set_page_owner_migrate_reason(newpage, reason);

-out:
if (rc != -EAGAIN) {
/*
* A page that has been migrated has all references
@@ -1179,20 +1267,7 @@ static int unmap_and_move(new_page_t get_new_page,
* we want to retry.
*/
if (rc == MIGRATEPAGE_SUCCESS) {
- /*
- * Compaction can migrate also non-LRU pages which are
- * not accounted to NR_ISOLATED_*. They can be recognized
- * as __PageMovable
- */
- if (likely(!__PageMovable(page)))
- mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
- page_is_file_lru(page), -thp_nr_pages(page));
-
- if (reason != MR_MEMORY_FAILURE)
- /*
- * We release the page in page_handle_poison.
- */
- put_page(page);
+ migrate_page_done(page, reason);
} else {
if (rc != -EAGAIN)
list_add_tail(&page->lru, ret);
@@ -1405,6 +1480,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
int pass = 0;
bool is_thp = false;
struct page *page;
+ struct page *newpage = NULL;
struct page *page2;
int rc, nr_subpages;
LIST_HEAD(ret_pages);
@@ -1493,9 +1569,13 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
if (PageHuge(page))
continue;

- rc = unmap_and_move(get_new_page, put_new_page,
- private, page, pass > 2, mode,
+ rc = migrate_page_unmap(get_new_page, put_new_page, private,
+ page, &newpage, pass > 2, mode,
reason, &ret_pages);
+ if (rc == MIGRATEPAGE_UNMAP)
+ rc = migrate_page_move(put_new_page, private,
+ page, newpage, mode,
+ reason, &ret_pages);
/*
* The rules are:
* Success: page will be freed
--
2.35.1