linux-kernel - [Patch v4 4/4] mm/migrate.c: unify "not queued for migration" handling in do_pages

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Message-Id: <20200129221616.25432-5-richardw.yang@linux.intel.com>
Date:   Thu, 30 Jan 2020 06:16:16 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, mhocko@...e.com,
        yang.shi@...ux.alibaba.com, rientjes@...gle.com, david@...hat.com,
        Wei Yang <richardw.yang@...ux.intel.com>
Subject: [Patch v4 4/4] mm/migrate.c: unify "not queued for migration" handling in do_pages_move()

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@...hat.com rephrase changelog]

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Reviewed-by: David Hildenbrand <david@...hat.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