Re: [PATCH V3] mm: memory hot-add: memory can not be added to movable zone defaultly

[Changsheng Liu]

å 2015/8/27 17:29, Vlastimil Babka åé:
> On 08/27/2015 10:54 AM, Changsheng Liu wrote:
> > From: Changsheng Liu <liuchangcheng@xxxxxxxxxx>
> >
> > After the user config CONFIG_MOVABLE_NODE and movable_node kernel 
> > option,
> > When the memory is hot added, should_add_memory_movable() return 0
> > because all zones including movable zone are empty,
> > so the memory that was hot added will be added  to the normal zone
> > and the normal zone will be created firstly.
> > But we want the whole node to be added to movable zone defaultly.
>
> OK it seems current behavior indeed goes against the expectations of 
> setting movable_node.
>
> > So we change should_add_memory_movable(): if the user config
> > CONFIG_MOVABLE_NODE and movable_node kernel option
> > it will always return 1 and all zones is empty at the same time,
> > so that the movable zone will be created firstly
> > and then the whole node will be added to movable zone defaultly.
> > If we want the node to be added to normal zone,
> > we can do it as follows:
> > "echo online_kernel > /sys/devices/system/memory/memoryXXX/state"
> >
> > If the memory is added to movable zone defaultly,
> > the user can offline it and add it to other zone again.
>
> Was this tested to really work as well? Per Yasuaki's explanation in 
> v2, you shouldn't create ZONE_MOVABLE before ZONE_NORMAL.
    We will test it more fully.
    There is on limit written in Documentation/memory-hotplug.txt when 
move the memory from movable zone to normal zone:
    echo online_kernel > /sys/devices/system/memory/memoryXXX/state
    (NOTE: current limit: this memory block must be adjacent to 
ZONE_NORMAL)

    The zone will be created as follows:
    First,all zones have been initialized,but all zones are empty, then 
the should_add_memory_movable() return 1 so the movable is created and 
add the whole node to movable zone.
            empty                 whole node's memory
    |-------------------|-------------------------------|---
     ZONE_NORMAL     ZONE_MOVABLE

   when we  move the memory to normal zone
empty whole node's memory
|--------------------|----------------------------------------------------:-------------------------------------------|
                                  one memory block ajacent to 
ZONE_NORMAL  :
     ZONE_NORMAL   ZONE_MOVABLE            :
                                      :
                                 one memory block 
                                            :    whole node  - one 
memory block
|-------------------------------------------------------------------------|-------------------------------------------|
     ZONE_NORMAL                           ZONE_MOVABLE
> > But if the memory is added to normal zone defaultly,
> > the user will not offline the memory used by kernel.
> >
> > Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
> Interesting...
>
> > Signed-off-by: Changsheng Liu <liuchangcheng@xxxxxxxxxx>i
> > Tested-by: Dongdong Fan <fandd@xxxxxxxxxx>
> > ---
> >   mm/memory_hotplug.c |    3 +++
> >   1 files changed, 3 insertions(+), 0 deletions(-)
> >
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 26fbba7..b5f14fa 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1198,6 +1198,9 @@ static int should_add_memory_movable(int nid, 
> > u64 start, u64 size)
> >       pg_data_t *pgdat = NODE_DATA(nid);
> >       struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
> >
> > +    if (movable_node_is_enabled())
> > +        return 1;
> > +
> >       if (zone_is_empty(movable_zone))
> >           return 0;
>
> .

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