[v2 PATCH 0/5] mm: misc migrate cleanup and improvement

[v2 PATCH 0/5] mm: misc migrate cleanup and improvement

[Yang Shi]

Some misc migrate code cleanup and improvement.

v2: * Fixed the comments from Zi Yan
    * Collected Reviewed-by


Yang Shi (5):
      mm: truncate_complete_page is not existed anymore
      mm: migrate: simplify the logic for handling permanent failure
      mm: migrate: skip shared exec THP for NUMA balancing
      mm: migrate: clean up migrate_prep{_local}
      mm: migrate: return -ENOSYS if THP migration is unsupported

 include/linux/migrate.h |   4 +--
 mm/mempolicy.c          |   8 ++---
 mm/migrate.c            | 158 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------
 mm/vmscan.c             |   2 +-
 4 files changed, 108 insertions(+), 64 deletions(-)

[v2 PATCH 1/5] mm: truncate_complete_page is not existed anymore

[Yang Shi]

The commit 9f4e41f4717832e34cca153ced62b4a1d7e26c0e ("mm: refactor
truncate_complete_page()") refactored truncate_complete_page(), and it
is not existed anymore, correct the comment in vmscan and migrate to avoid
confusion.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/migrate.c | 2 +-
 mm/vmscan.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 5ca5842df5db..8a2e7e19e27b 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1106,7 +1106,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	 * and treated as swapcache but it has no rmap yet.
 	 * Calling try_to_unmap() against a page->mapping==NULL page will
 	 * trigger a BUG.  So handle it here.
-	 * 2. An orphaned page (see truncate_complete_page) might have
+	 * 2. An orphaned page (see truncate_cleanup_page) might have
 	 * fs-private metadata. The page can be picked up due to memory
 	 * offlining.  Everywhere else except page reclaim, the page is
 	 * invisible to the vm, so the page can not be migrated.  So try to
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b8f0e059767..165cca87edc8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1393,7 +1393,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		 *
 		 * Rarely, pages can have buffers and no ->mapping.  These are
 		 * the pages which were not successfully invalidated in
-		 * truncate_complete_page().  We try to drop those buffers here
+		 * truncate_cleanup_page().  We try to drop those buffers here
 		 * and if that worked, and the page is no longer mapped into
 		 * process address space (page_count == 1) it can be freed.
 		 * Otherwise, leave the page on the LRU so it is swappable.
-- 
2.26.2

[v2 PATCH 2/5] mm: migrate: simplify the logic for handling permanent failure

[Yang Shi]

When unmap_and_move{_huge_page}() returns !-EAGAIN and !MIGRATEPAGE_SUCCESS,
the page would be put back to LRU or proper list if it is non-LRU movable
page.  But, the callers always call putback_movable_pages() to put the
failed pages back later on, so it seems not very efficient to put every
single page back immediately, and the code looks convoluted.

Put the failed page on a separate list, then splice the list to migrate
list when all pages are tried.  It is the caller's responsibility to
call putback_movable_pages() to handle failures.  This also makes the
code simpler and more readable.

After the change the rules are:
    * Success: non hugetlb page will be freed, hugetlb page will be put
               back
    * -EAGAIN: stay on the from list
    * -ENOMEM: stay on the from list
    * Other errno: put on ret_pages list then splice to from list

The from list would be empty iff all pages are migrated successfully, it
was not so before.  This has no impact to current existing callsites.

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/migrate.c | 68 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 38 insertions(+), 30 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 8a2e7e19e27b..d7167f7107bd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1169,7 +1169,8 @@ 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)
+				   enum migrate_reason reason,
+				   struct list_head *ret)
 {
 	int rc = MIGRATEPAGE_SUCCESS;
 	struct page *newpage = NULL;
@@ -1206,7 +1207,14 @@ static int unmap_and_move(new_page_t get_new_page,
 		 * migrated will have kept its references and be restored.
 		 */
 		list_del(&page->lru);
+	}
 
+	/*
+	 * If migration is successful, releases reference grabbed during
+	 * isolation. Otherwise, restore the page to right list unless
+	 * 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
@@ -1215,35 +1223,16 @@ static int unmap_and_move(new_page_t get_new_page,
 		if (likely(!__PageMovable(page)))
 			mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
 					page_is_file_lru(page), -thp_nr_pages(page));
-	}
 
-	/*
-	 * If migration is successful, releases reference grabbed during
-	 * isolation. Otherwise, restore the page to right list unless
-	 * we want to retry.
-	 */
-	if (rc == MIGRATEPAGE_SUCCESS) {
 		if (reason != MR_MEMORY_FAILURE)
 			/*
 			 * We release the page in page_handle_poison.
 			 */
 			put_page(page);
 	} else {
-		if (rc != -EAGAIN) {
-			if (likely(!__PageMovable(page))) {
-				putback_lru_page(page);
-				goto put_new;
-			}
+		if (rc != -EAGAIN)
+			list_add_tail(&page->lru, ret);
 
-			lock_page(page);
-			if (PageMovable(page))
-				putback_movable_page(page);
-			else
-				__ClearPageIsolated(page);
-			unlock_page(page);
-			put_page(page);
-		}
-put_new:
 		if (put_new_page)
 			put_new_page(newpage, private);
 		else
@@ -1274,7 +1263,8 @@ static int unmap_and_move(new_page_t get_new_page,
 static int unmap_and_move_huge_page(new_page_t get_new_page,
 				free_page_t put_new_page, unsigned long private,
 				struct page *hpage, int force,
-				enum migrate_mode mode, int reason)
+				enum migrate_mode mode, int reason,
+				struct list_head *ret)
 {
 	int rc = -EAGAIN;
 	int page_was_mapped = 0;
@@ -1290,7 +1280,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	 * kicking migration.
 	 */
 	if (!hugepage_migration_supported(page_hstate(hpage))) {
-		putback_active_hugepage(hpage);
+		list_move_tail(&hpage->lru, ret);
 		return -ENOSYS;
 	}
 
@@ -1372,8 +1362,10 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 out_unlock:
 	unlock_page(hpage);
 out:
-	if (rc != -EAGAIN)
+	if (rc == MIGRATEPAGE_SUCCESS)
 		putback_active_hugepage(hpage);
+	else if (rc != -EAGAIN && rc != MIGRATEPAGE_SUCCESS)
+		list_move_tail(&hpage->lru, ret);
 
 	/*
 	 * If migration was not successful and there's a freeing callback, use
@@ -1404,8 +1396,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
  *
  * The function returns after 10 attempts or if no pages are movable any more
  * because the list has become empty or no retryable pages exist any more.
- * The caller should call putback_movable_pages() to return pages to the LRU
- * or free list only if ret != 0.
+ * It is caller's responsibility to call putback_movable_pages() to return pages
+ * to the LRU or free list only if ret != 0.
  *
  * Returns the number of pages that were not migrated, or an error code.
  */
@@ -1426,6 +1418,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	struct page *page2;
 	int swapwrite = current->flags & PF_SWAPWRITE;
 	int rc, nr_subpages;
+	LIST_HEAD(ret_pages);
 
 	if (!swapwrite)
 		current->flags |= PF_SWAPWRITE;
@@ -1448,12 +1441,21 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			if (PageHuge(page))
 				rc = unmap_and_move_huge_page(get_new_page,
 						put_new_page, private, page,
-						pass > 2, mode, reason);
+						pass > 2, mode, reason,
+						&ret_pages);
 			else
 				rc = unmap_and_move(get_new_page, put_new_page,
 						private, page, pass > 2, mode,
-						reason);
-
+						reason, &ret_pages);
+			/*
+			 * The rules are:
+			 *	Success: non hugetlb page will be freed, hugetlb
+			 *		 page will be put back
+			 *	-EAGAIN: stay on the from list
+			 *	-ENOMEM: stay on the from list
+			 *	Other errno: put on ret_pages list then splice to
+			 *		     from list
+			 */
 			switch(rc) {
 			case -ENOMEM:
 				/*
@@ -1519,6 +1521,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	nr_thp_failed += thp_retry;
 	rc = nr_failed;
 out:
+	/*
+	 * Put the permanent failure page back to migration list, they
+	 * will be put back to the right list by the caller.
+	 */
+	list_splice(&ret_pages, from);
+
 	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
 	count_vm_events(PGMIGRATE_FAIL, nr_failed);
 	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
-- 
2.26.2

[v2 PATCH 3/5] mm: migrate: skip shared exec THP for NUMA balancing

[Yang Shi]

The NUMA balancing skip shared exec base page.  Since
CONFIG_READ_ONLY_THP_FOR_FS was introduced, there are probably shared
exec THP, so skip such THPs for NUMA balancing as well.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/migrate.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index d7167f7107bd..1b103e801fe4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2069,6 +2069,16 @@ bool pmd_trans_migrating(pmd_t pmd)
 	return PageLocked(page);
 }
 
+static inline bool is_shared_exec_page(struct vm_area_struct *vma,
+				       struct page *page)
+{
+	if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
+	    (vma->vm_flags & VM_EXEC))
+		return true;
+
+	return false;
+}
+
 /*
  * Attempt to migrate a misplaced page to the specified destination
  * node. Caller is expected to have an elevated reference count on
@@ -2086,8 +2096,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	 * Don't migrate file pages that are mapped in multiple processes
 	 * with execute permissions as they are probably shared libraries.
 	 */
-	if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
-	    (vma->vm_flags & VM_EXEC))
+	if (is_shared_exec_page(vma, page))
 		goto out;
 
 	/*
@@ -2142,6 +2151,10 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	int page_lru = page_is_file_lru(page);
 	unsigned long start = address & HPAGE_PMD_MASK;
 
+	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
+	    is_shared_exec_page(vma, page))
+		goto out;
+
 	new_page = alloc_pages_node(node,
 		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
 		HPAGE_PMD_ORDER);
@@ -2253,6 +2266,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 
 out_unlock:
 	unlock_page(page);
+out:
 	put_page(page);
 	return 0;
 }
-- 
2.26.2

Re: [v2 PATCH 3/5] mm: migrate: skip shared exec THP for NUMA balancing

[Matthew Wilcox]

On Tue, Nov 10, 2020 at 10:12:48AM -0800, Yang Shi wrote:
> @@ -2142,6 +2151,10 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
>  	int page_lru = page_is_file_lru(page);
>  	unsigned long start = address & HPAGE_PMD_MASK;
>  
> +	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> +	    is_shared_exec_page(vma, page))
> +		goto out;

Why include the IS_ENABLED() check?  Once the ~50 patches I have pending
go in, shared executable THPs can exist without this option.  And can't
we have executables on tmpfs today without this option too?

Re: [v2 PATCH 3/5] mm: migrate: skip shared exec THP for NUMA balancing

[Yang Shi]

On Tue, Nov 10, 2020 at 10:16 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Nov 10, 2020 at 10:12:48AM -0800, Yang Shi wrote:
> > @@ -2142,6 +2151,10 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> >       int page_lru = page_is_file_lru(page);
> >       unsigned long start = address & HPAGE_PMD_MASK;
> >
> > +     if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> > +         is_shared_exec_page(vma, page))
> > +             goto out;
>
> Why include the IS_ENABLED() check?  Once the ~50 patches I have pending
> go in, shared executable THPs can exist without this option.  And can't
> we have executables on tmpfs today without this option too?

Aha, yes, thanks for reminding. I had the patches baked in my tree
before your patches were posted.

We could have executables on tmpfs w/o that config. Will remove it. Thanks.

[v2 PATCH 4/5] mm: migrate: clean up migrate_prep{_local}

[Yang Shi]

The migrate_prep{_local} never fails, so it is pointless to have return
value and check the return value.

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/migrate.h | 4 ++--
 mm/mempolicy.c          | 8 ++------
 mm/migrate.c            | 8 ++------
 3 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 0f8d1583fa8e..4594838a0f7c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -45,8 +45,8 @@ extern struct page *alloc_migration_target(struct page *page, unsigned long priv
 extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
 extern void putback_movable_page(struct page *page);
 
-extern int migrate_prep(void);
-extern int migrate_prep_local(void);
+extern void migrate_prep(void);
+extern void migrate_prep_local(void);
 extern void migrate_page_states(struct page *newpage, struct page *page);
 extern void migrate_page_copy(struct page *newpage, struct page *page);
 extern int migrate_huge_page_move_mapping(struct address_space *mapping,
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3ca4898f3f24..8cf96bd21341 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1114,9 +1114,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 	int err;
 	nodemask_t tmp;
 
-	err = migrate_prep();
-	if (err)
-		return err;
+	migrate_prep();
 
 	mmap_read_lock(mm);
 
@@ -1315,9 +1313,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 
 	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
 
-		err = migrate_prep();
-		if (err)
-			goto mpol_out;
+		migrate_prep();
 	}
 	{
 		NODEMASK_SCRATCH(scratch);
diff --git a/mm/migrate.c b/mm/migrate.c
index 1b103e801fe4..693bf06448ad 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -62,7 +62,7 @@
  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
  * undesirable, use migrate_prep_local()
  */
-int migrate_prep(void)
+void migrate_prep(void)
 {
 	/*
 	 * Clear the LRU lists so pages can be isolated.
@@ -71,16 +71,12 @@ int migrate_prep(void)
 	 * pages that may be busy.
 	 */
 	lru_add_drain_all();
-
-	return 0;
 }
 
 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
-int migrate_prep_local(void)
+void migrate_prep_local(void)
 {
 	lru_add_drain();
-
-	return 0;
 }
 
 int isolate_movable_page(struct page *page, isolate_mode_t mode)
-- 
2.26.2

[v2 PATCH 5/5] mm: migrate: return -ENOSYS if THP migration is unsupported

[Yang Shi]

In the current implementation unmap_and_move() would return -ENOMEM if
THP migration is unsupported, then the THP will be split.  If split is
failed just exit without trying to migrate other pages.  It doesn't make
too much sense since there may be enough free memory to migrate other
pages and there may be a lot base pages on the list.

Return -ENOSYS to make consistent with hugetlb.  And if THP split is
failed just skip and try other pages on the list.

Just skip the whole list and exit when free memory is really low.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/migrate.c | 62 ++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 693bf06448ad..d110af76fa4d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1172,7 +1172,7 @@ static int unmap_and_move(new_page_t get_new_page,
 	struct page *newpage = NULL;
 
 	if (!thp_migration_supported() && PageTransHuge(page))
-		return -ENOMEM;
+		return -ENOSYS;
 
 	if (page_count(page) == 1) {
 		/* page was freed from under us. So we are done. */
@@ -1376,6 +1376,20 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	return rc;
 }
 
+static inline int try_split_thp(struct page *page, struct page **page2,
+				struct list_head *from)
+{
+	int rc = 0;
+
+	lock_page(page);
+	rc = split_huge_page_to_list(page, from);
+	unlock_page(page);
+	if (!rc)
+		list_safe_reset_next(page, *page2, lru);
+
+	return rc;
+}
+
 /*
  * migrate_pages - migrate the pages specified in a list, to the free pages
  *		   supplied as the target for the page migration
@@ -1453,24 +1467,40 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			 *		     from list
 			 */
 			switch(rc) {
+			/*
+			 * THP migration might be unsupported or the
+			 * allocation could've failed so we should
+			 * retry on the same page with the THP split
+			 * to base pages.
+			 *
+			 * Head page is retried immediately and tail
+			 * pages are added to the tail of the list so
+			 * we encounter them after the rest of the list
+			 * is processed.
+			 */
+			case -ENOSYS:
+				/* THP migration is unsupported */
+				if (is_thp) {
+					if (!try_split_thp(page, &page2, from)) {
+						nr_thp_split++;
+						goto retry;
+					}
+
+					nr_thp_failed++;
+					nr_failed += nr_subpages;
+					break;
+				}
+
+				/* Hugetlb migration is unsupported */
+				nr_failed++;
+				break;
 			case -ENOMEM:
 				/*
-				 * THP migration might be unsupported or the
-				 * allocation could've failed so we should
-				 * retry on the same page with the THP split
-				 * to base pages.
-				 *
-				 * Head page is retried immediately and tail
-				 * pages are added to the tail of the list so
-				 * we encounter them after the rest of the list
-				 * is processed.
+				 * When memory is low, don't bother to try to migrate
+				 * other pages, just exit.
 				 */
 				if (is_thp) {
-					lock_page(page);
-					rc = split_huge_page_to_list(page, from);
-					unlock_page(page);
-					if (!rc) {
-						list_safe_reset_next(page, page2, lru);
+					if (!try_split_thp(page, &page2, from)) {
 						nr_thp_split++;
 						goto retry;
 					}
@@ -1498,7 +1528,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				break;
 			default:
 				/*
-				 * Permanent failure (-EBUSY, -ENOSYS, etc.):
+				 * Permanent failure (-EBUSY, etc.):
 				 * unlike -EAGAIN case, the failed page is
 				 * removed from migration page list and not
 				 * retried in the next outer loop.
-- 
2.26.2