| From 5984fabb6e82d9ab4e6305cb99694c85d46de8ae Mon Sep 17 00:00:00 2001 |
| From: Yang Shi <yang.shi@linux.alibaba.com> |
| Date: Thu, 30 Jan 2020 22:11:24 -0800 |
| Subject: mm: move_pages: report the number of non-attempted pages |
| |
| From: Yang Shi <yang.shi@linux.alibaba.com> |
| |
| commit 5984fabb6e82d9ab4e6305cb99694c85d46de8ae upstream. |
| |
| 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. |
| |
| Link: http://lkml.kernel.org/r/1580160527-109104-1-git-send-email-yang.shi@linux.alibaba.com |
| Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") |
| Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> |
| Suggested-by: Michal Hocko <mhocko@suse.com> |
| Acked-by: Michal Hocko <mhocko@suse.com> |
| Reviewed-by: Wei Yang <richardw.yang@linux.intel.com> |
| Cc: <stable@vger.kernel.org> [4.17+] |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| mm/migrate.c | 25 +++++++++++++++++++++++-- |
| 1 file changed, 23 insertions(+), 2 deletions(-) |
| |
| --- a/mm/migrate.c |
| +++ b/mm/migrate.c |
| @@ -1623,8 +1623,19 @@ static int do_pages_move(struct mm_struc |
| 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; |
| @@ -1655,8 +1666,11 @@ static int do_pages_move(struct mm_struc |
| 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) |
| @@ -1670,6 +1684,13 @@ out_flush: |
| |
| /* 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 >= 0) |