linux-kernel - Re: [PATCH] mm/memory_hotplug: just build zonelist for new added node

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Message-ID: <CADZGycbxQq3TewS7VBDo9PzeY7nm1scYD=teFQaURKVEdoBGYA@mail.gmail.com>
Date:   Wed, 28 Jun 2017 15:28:59 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/memory_hotplug: just build zonelist for new added node

On Wed, Jun 28, 2017 at 3:06 PM, Vlastimil Babka <vbabka@...e.cz> wrote:
> On 06/26/2017 05:58 AM, Wei Yang wrote:
>> In commit (9adb62a5df9c0fbef7) "mm/hotplug: correctly setup fallback
>> zonelists when creating new pgdat" tries to build the correct zonelist for
>> a new added node, while it is not necessary to rebuild it for already exist
>> nodes.
>>
>> In build_zonelists(), it will iterate on nodes with memory. For a new added
>> node, it will have memory until node_states_set_node() is called in
>
>         it will not have memory
>

No memory at this point.

> right?
>
>> online_pages().
>>
>> This patch will avoid to rebuild the zonelists for already exist nodes.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>
> Sounds correct, as far as the memory hotplug mess allows.
>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>
> Some style nitpicks below:
>
>> ---
>>  mm/page_alloc.c | 16 +++++++++-------
>>  1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 560eafe8234d..fc8181b44fd8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5200,15 +5200,17 @@ static int __build_all_zonelists(void *data)
>>       memset(node_load, 0, sizeof(node_load));
>>  #endif
>>
>> -     if (self && !node_online(self->node_id)) {
>> +     /* This node is hotadded and no memory preset yet.
>
> On multiline comments, the first line should be empty after "/*"
>

Thanks, I will pay attention next time.

> But I see Andrew already fixed that.
>
>> +      * So just build zonelists is fine, no need to touch other nodes.
>> +      */
>> +     if (self && !node_online(self->node_id))
>>               build_zonelists(self);
>> -     }
>> -
>> -     for_each_online_node(nid) {
>> -             pg_data_t *pgdat = NODE_DATA(nid);
>> +     else
>> +             for_each_online_node(nid) {
>> +                     pg_data_t *pgdat = NODE_DATA(nid);
>>
>> -             build_zonelists(pgdat);
>> -     }
>> +                     build_zonelists(pgdat);
>> +             }
>
> Personally I would use { } for the else block, and thus leave them also
> for the if block, not sure if this is recommended by the style guide though.
>

I am not quite sure about this. The checkpatch.py script doesn't complain.

Thanks for your comment again~

>>       /*
>>        * Initialize the boot_pagesets that are going to be used
>>
>