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Date:   Wed, 29 Jan 2020 08:46:37 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, mhocko@suse.com,
        yang.shi@linux.alibaba.com, rientjes@google.com
Subject: Re: [Patch v2 3/4] mm/migrate.c: check pagelist in
 move_pages_and_store_status()
Message-ID: <20200129004637.GD12835@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <20200122011647.13636-1-richardw.yang@linux.intel.com>
 <20200122011647.13636-4-richardw.yang@linux.intel.com>
 <f7f70c42-a9a6-6c84-cdb5-230205703ddf@redhat.com>
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On Tue, Jan 28, 2020 at 11:21:13AM +0100, David Hildenbrand wrote:
>On 22.01.20 02:16, Wei Yang wrote:
>> When pagelist is empty, it is not necessary to do the move and store.
>> Also it consolidate the empty list check in one place.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> ---
>>  mm/migrate.c | 9 +++------
>>  1 file changed, 3 insertions(+), 6 deletions(-)
>> 
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index a4d3bd6475e1..80d2bba57265 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1499,9 +1499,6 @@ static int do_move_pages_to_node(struct mm_struct *mm,
>>  {
>>  	int err;
>>  
>> -	if (list_empty(pagelist))
>> -		return 0;
>> -
>>  	err = migrate_pages(pagelist, alloc_new_node_page, NULL, node,
>>  			MIGRATE_SYNC, MR_SYSCALL);
>>  	if (err)
>> @@ -1589,6 +1586,9 @@ static int move_pages_and_store_status(struct mm_struct *mm, int node,
>>  {
>>  	int err;
>>  
>> +	if (list_empty(pagelist))
>> +		return 0;
>> +
>>  	err = do_move_pages_to_node(mm, pagelist, node);
>>  	if (err)
>>  		return err;
>> @@ -1676,9 +1676,6 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>>  		current_node = NUMA_NO_NODE;
>>  	}
>>  out_flush:
>> -	if (list_empty(&pagelist))
>> -		return err;
>
>
>Am I wrong or are you discarding an error here? (err could be !0)
>

This is not obvious in this code snippet. If you look into the source code, it
might help you get the whole picture.

The following comment says:

  Make sure we do not overwrite the existing error

So we didn't eat error here.

>
>-- 
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me