[Patch v4 0/4] cleanup on do_pages_move()

[Patch v4 0/4] cleanup on do_pages_move()

[Wei Yang]

The logic in do_pages_move() is a little mess for audience to read and has
some potential error on handling the return value. Especially there are
three calls on do_move_pages_to_node() and store_status() with almost the
same form.

This patch set tries to make the code a little friendly for audience by
consolidate the calls.

v4:
  * rephrase changelog based on suggestion from David Hildenbrand
  * trivial change on code style and comment
v3:
  * rebase on top of Yang Shi's fix "mm: move_pages: report the number of
    non-attempted pages"
v2:
  * remove some unnecessary cleanup

Wei Yang (4):
  mm/migrate.c: no need to check for i > start in do_pages_move()
  mm/migrate.c: wrap do_move_pages_to_node() and store_status()
  mm/migrate.c: check pagelist in move_pages_and_store_status()
  mm/migrate.c: unify "not queued for migration" handling in
    do_pages_move()

 mm/migrate.c | 54 ++++++++++++++++++++++++++--------------------------
 1 file changed, 27 insertions(+), 27 deletions(-)

-- 
2.17.1

[Patch v4 1/4] mm/migrate.c: no need to check for i > start in do_pages_move()

[Wei Yang]

At this point, we always have i >= start. If i == start, store_status()
will return 0. So we can drop the check for i > start.

[david@redhat.com rephrase changelog]

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/migrate.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 430fdccc733e..4c2a21856717 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1661,11 +1661,9 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		err = do_move_pages_to_node(mm, &pagelist, current_node);
 		if (err)
 			goto out;
-		if (i > start) {
-			err = store_status(status, start, current_node, i - start);
-			if (err)
-				goto out;
-		}
+		err = store_status(status, start, current_node, i - start);
+		if (err)
+			goto out;
 		current_node = NUMA_NO_NODE;
 	}
 out_flush:
-- 
2.17.1

[Patch v4 2/4] mm/migrate.c: wrap do_move_pages_to_node() and store_status()

[Wei Yang]

Usually, do_move_pages_to_node() and store_status() are used in
combination. We have three similar call sites.

Let's provide a wrapper for both function calls -
move_pages_and_store_status - to make the calling code easier to
maintain and fix (as noted by Yang Shi, the return value handling of
do_move_pages_to_node() has a flaw).

[david@redhat.com rephrase changelog]

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/migrate.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 4c2a21856717..92e8c9396368 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1583,6 +1583,18 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
 	return err;
 }
 
+static int move_pages_and_store_status(struct mm_struct *mm, int node,
+		struct list_head *pagelist, int __user *status,
+		int start, int nr)
+{
+	int err;
+
+	err = do_move_pages_to_node(mm, pagelist, node);
+	if (err)
+		return err;
+	return store_status(status, start, node, nr);
+}
+
 /*
  * Migrate an array of page address onto an array of nodes and fill
  * the corresponding array of status.
@@ -1626,10 +1638,8 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 			current_node = node;
 			start = i;
 		} else if (node != current_node) {
-			err = do_move_pages_to_node(mm, &pagelist, current_node);
-			if (err)
-				goto out;
-			err = store_status(status, start, current_node, i - start);
+			err = move_pages_and_store_status(mm, current_node,
+					&pagelist, status, start, i - start);
 			if (err)
 				goto out;
 			start = i;
@@ -1658,10 +1668,8 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		if (err)
 			goto out_flush;
 
-		err = do_move_pages_to_node(mm, &pagelist, current_node);
-		if (err)
-			goto out;
-		err = store_status(status, start, current_node, i - start);
+		err = move_pages_and_store_status(mm, current_node, &pagelist,
+				status, start, i - start);
 		if (err)
 			goto out;
 		current_node = NUMA_NO_NODE;
@@ -1671,9 +1679,8 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		return err;
 
 	/* Make sure we do not overwrite the existing error */
-	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
-	if (!err1)
-		err1 = store_status(status, start, current_node, i - start);
+	err1 = move_pages_and_store_status(mm, current_node, &pagelist,
+				status, start, i - start);
 	if (err >= 0)
 		err = err1;
 out:
-- 
2.17.1

[Patch v4 3/4] mm/migrate.c: check pagelist in move_pages_and_store_status()

[Wei Yang]

When pagelist is empty, it is not necessary to do the move and store.
Also it consolidate the empty list check in one place.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/migrate.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 92e8c9396368..981916007b4f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1499,9 +1499,6 @@ static int do_move_pages_to_node(struct mm_struct *mm,
 {
 	int err;
 
-	if (list_empty(pagelist))
-		return 0;
-
 	err = migrate_pages(pagelist, alloc_new_node_page, NULL, node,
 			MIGRATE_SYNC, MR_SYSCALL);
 	if (err)
@@ -1589,6 +1586,9 @@ static int move_pages_and_store_status(struct mm_struct *mm, int node,
 {
 	int err;
 
+	if (list_empty(pagelist))
+		return 0;
+
 	err = do_move_pages_to_node(mm, pagelist, node);
 	if (err)
 		return err;
@@ -1675,9 +1675,6 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		current_node = NUMA_NO_NODE;
 	}
 out_flush:
-	if (list_empty(&pagelist))
-		return err;
-
 	/* Make sure we do not overwrite the existing error */
 	err1 = move_pages_and_store_status(mm, current_node, &pagelist,
 				status, start, i - start);
-- 
2.17.1

[Patch v4 4/4] mm/migrate.c: unify "not queued for migration" handling in do_pages_move()

[Wei Yang]

It can currently happen that we store the status of a page twice:
* Once we detect that it is already on the target node
* Once we moved a bunch of pages, and a page that's already on the
  target node is contained in the current interval.

Let's simplify the code and always call do_move_pages_to_node() in
case we did not queue a page for migration. Note that pages that are
already on the target node are not added to the pagelist and are,
therefore, ignored by do_move_pages_to_node() - there is no functional
change.

The status of such a page is now only stored once.

[david@redhat.com rephrase changelog]

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/migrate.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 981916007b4f..7c850fe5a1a8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1653,18 +1653,16 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		err = add_page_for_migration(mm, addr, current_node,
 				&pagelist, flags & MPOL_MF_MOVE_ALL);
 
-		if (!err) {
-			/* The page is already on the target node */
-			err = store_status(status, i, current_node, 1);
-			if (err)
-				goto out_flush;
-			continue;
-		} else if (err > 0) {
+		if (err > 0) {
 			/* The page is successfully queued for migration */
 			continue;
 		}
 
-		err = store_status(status, i, err, 1);
+		/*
+		 * If the page is already on the target node (!err), store the
+		 * node, otherwise, store the err.
+		 */
+		err = store_status(status, i, err ? : current_node, 1);
 		if (err)
 			goto out_flush;
 
-- 
2.17.1