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* [v4 PATCH] mm: move_pages: report the number of non-attempted pages
@ 2020-01-27 21:28 Yang Shi
  2020-01-28  0:34 ` Wei Yang
  0 siblings, 1 reply; 2+ messages in thread
From: Yang Shi @ 2020-01-27 21:28 UTC (permalink / raw)
  To: mhocko, richardw.yang, willy, akpm
  Cc: yang.shi, linux-mm, linux-kernel, stable

Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"),
the semantic of move_pages() has changed to return the number of
non-migrated pages if they were result of a non-fatal reasons (usually a
busy page).  This was an unintentional change that hasn't been noticed
except for LTP tests which checked for the documented behavior.

There are two ways to go around this change.  We can even get back to the
original behavior and return -EAGAIN whenever migrate_pages is not able
to migrate pages due to non-fatal reasons.  Another option would be to
simply continue with the changed semantic and extend move_pages
documentation to clarify that -errno is returned on an invalid input or
when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the
number of pages that couldn't have been migrated due to ephemeral
reasons (e.g. page is pinned or locked for other reasons).

This patch implements the second option because this behavior is in
place for some time without anybody complaining and possibly new users
depending on it.  Also it allows to have a slightly easier error handling
as the caller knows that it is worth to retry when err > 0.

But since the new semantic would be aborted immediately if migration is
failed due to ephemeral reasons, need include the number of non-attempted
pages in the return value too.

Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
Suggested-by: Michal Hocko <mhocko@suse.com>
Acked-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>
---
v4: Fixed some typo and grammar errors caught by Willy
v3: Rephrased the commit log per Michal and added Michal's Acked-by
v2: Rebased on top of the latest mainline kernel per Andrew

 mm/migrate.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 86873b6..2530860 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1627,8 +1627,19 @@ 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 to incude the rest of the
+				 * nr_pages that have not been 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 +1670,11 @@ 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 +1688,13 @@ 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:
+	 *     - If the above loop is done gracefully all pages have been
+	 *       attempted.
+	 *     - If the above loop is aborted it means a fatal error
+	 *       happened, should return ret.
+	 */
 	if (!err1)
 		err1 = store_status(status, start, current_node, i - start);
 	if (!err)
-- 
1.8.3.1


^ permalink raw reply related	[flat|nested] 2+ messages in thread

* Re: [v4 PATCH] mm: move_pages: report the number of non-attempted pages
  2020-01-27 21:28 [v4 PATCH] mm: move_pages: report the number of non-attempted pages Yang Shi
@ 2020-01-28  0:34 ` Wei Yang
  0 siblings, 0 replies; 2+ messages in thread
From: Wei Yang @ 2020-01-28  0:34 UTC (permalink / raw)
  To: Yang Shi
  Cc: mhocko, richardw.yang, willy, akpm, linux-mm, linux-kernel, stable

On Tue, Jan 28, 2020 at 05:28:47AM +0800, Yang Shi wrote:
>Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"),
>the semantic of move_pages() has changed to return the number of
>non-migrated pages if they were result of a non-fatal reasons (usually a
>busy page).  This was an unintentional change that hasn't been noticed
>except for LTP tests which checked for the documented behavior.
>
>There are two ways to go around this change.  We can even get back to the
>original behavior and return -EAGAIN whenever migrate_pages is not able
>to migrate pages due to non-fatal reasons.  Another option would be to
>simply continue with the changed semantic and extend move_pages
>documentation to clarify that -errno is returned on an invalid input or
>when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the
>number of pages that couldn't have been migrated due to ephemeral
>reasons (e.g. page is pinned or locked for other reasons).
>
>This patch implements the second option because this behavior is in
>place for some time without anybody complaining and possibly new users
>depending on it.  Also it allows to have a slightly easier error handling
>as the caller knows that it is worth to retry when err > 0.
>
>But since the new semantic would be aborted immediately if migration is
>failed due to ephemeral reasons, need include the number of non-attempted
>pages in the return value too.
>
>Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
>Suggested-by: Michal Hocko <mhocko@suse.com>
>Acked-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>

Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

>---
>v4: Fixed some typo and grammar errors caught by Willy
>v3: Rephrased the commit log per Michal and added Michal's Acked-by
>v2: Rebased on top of the latest mainline kernel per Andrew
>
> mm/migrate.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
>diff --git a/mm/migrate.c b/mm/migrate.c
>index 86873b6..2530860 100644
>--- a/mm/migrate.c
>+++ b/mm/migrate.c
>@@ -1627,8 +1627,19 @@ 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 to incude the rest of the
>+				 * nr_pages that have not been 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 +1670,11 @@ 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 +1688,13 @@ 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:
>+	 *     - If the above loop is done gracefully all pages have been
>+	 *       attempted.
>+	 *     - If the above loop is aborted it means a fatal error
>+	 *       happened, should return ret.
>+	 */
> 	if (!err1)
> 		err1 = store_status(status, start, current_node, i - start);
> 	if (!err)
>-- 
>1.8.3.1

-- 
Wei Yang
Help you, Help me

^ permalink raw reply	[flat|nested] 2+ messages in thread

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