linux-kernel - Re: [PATCH] mm: move_pages: fix the return value if there are not-migrated pages

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Message-ID: <20200119025733.GG9745@richard>
Date:   Sun, 19 Jan 2020 10:57:33 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...e.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm: move_pages: fix the return value if there are
 not-migrated pages

On Sun, Jan 19, 2020 at 10:37:20AM +0800, Wei Yang wrote:
>On Sat, Jan 18, 2020 at 01:26:43PM +0800, Yang Shi wrote:
>>The do_move_pages_to_node() might return > 0 value, the number of pages
>>that are not migrated, then the value will be returned to userspace
>>directly.  But, move_pages() syscall would just return 0 or errno.  So,
>>we need reset the return value to 0 for such case as what pre-v4.17 did.
>>
>>Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
>>Cc: Michal Hocko <mhocko@...e.com>
>>Cc: Wei Yang <richardw.yang@...ux.intel.com>
>>Cc: <stable@...r.kernel.org>    [4.17+]
>>Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
>>---
>> mm/migrate.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>>diff --git a/mm/migrate.c b/mm/migrate.c
>>index 86873b6..3e75432 100644
>>--- a/mm/migrate.c
>>+++ b/mm/migrate.c
>>@@ -1659,8 +1659,11 @@ 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 = 0;
>> 			goto out;
>>+		}
>> 		if (i > start) {
>> 			err = store_status(status, start, current_node, i - start);
>> 			if (err)
>>-- 
>>1.8.3.1
>
>
>Hey, I am afraid you missed something. There are three calls of
>do_move_pages_to_node() in do_pages_move(). Why you just handle one return
>value? How about the other two?
>

Well, current logic in do_pages_move() is a little complicated to read.

I did a cleanup to make it easy to read and also friendly to do this fix.

If they look good to you, you could rebase your fix on top of them.

>-- 
>Wei Yang
>Help you, Help me

-- 
Wei Yang
Help you, Help me