Re: [v2 PATCH] mm: move_pages: report the number of non-attempted pages

[Wei Yang <richardw.yang@linux.intel.com>]

On Thu, Jan 23, 2020 at 07:38:51AM +0800, Yang Shi wrote:
>Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"),
>the semantic of move_pages() was changed to return the number of
>non-migrated pages (failed to migration) and the call would be aborted
>immediately if migrate_pages() returns positive value.  But it didn't
>report the number of pages that we even haven't attempted to migrate.
>So, fix it by including non-attempted pages in the return value.
>
>Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
>Suggested-by: Michal Hocko <mhocko@suse.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Cc: <stable@vger.kernel.org>    [4.17+]
>Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>---
>v2: Rebased on top of the latest mainline kernel per Andrew
>
> mm/migrate.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
>diff --git a/mm/migrate.c b/mm/migrate.c
>index 86873b6..9b8eb5d 100644
>--- a/mm/migrate.c
>+++ b/mm/migrate.c
>@@ -1627,8 +1627,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> 			start = i;
> 		} else if (node != current_node) {
> 			err = do_move_pages_to_node(mm, &pagelist, current_node);
>-			if (err)
>+			if (err) {
>+				/*
>+				 * Positive err means the number of failed
>+				 * pages to migrate.  Since we are going to
>+				 * abort and return the number of non-migrated
>+				 * pages, so need incude the rest of the
>+				 * nr_pages that have not attempted as well.
>+				 */
>+				if (err > 0)
>+					err += nr_pages - i - 1;
> 				goto out;
>+			}
> 			err = store_status(status, start, current_node, i - start);
> 			if (err)
> 				goto out;
>@@ -1659,8 +1669,11 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> 			goto out_flush;
> 
> 		err = do_move_pages_to_node(mm, &pagelist, current_node);
>-		if (err)
>+		if (err) {
>+			if (err > 0)
>+				err += nr_pages - i - 1;
> 			goto out;
>+		}
> 		if (i > start) {
> 			err = store_status(status, start, current_node, i - start);
> 			if (err)
>@@ -1674,6 +1687,13 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> 
> 	/* Make sure we do not overwrite the existing error */
> 	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
>+	/*
>+	 * Don't have to report non-attempted pages here since:

In previous comment, you use "non-migrated". Here is "non-attempted". What's
the difference?

>+	 *     - If the above loop is done gracefully there is not non-attempted
>+	 *       page.
>+	 *     - If the above loop is aborted to it means more fatal error
>+	 *       happened, should return err.
>+	 */
> 	if (!err1)
> 		err1 = store_status(status, start, current_node, i - start);
> 	if (!err)
>-- 
>1.8.3.1

-- 
Wei Yang
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