Re: [PATCH V2] mm:memory hot-add: memory can not been added to movable zone

[Changsheng Liu]

First, thanks very much for your review, I will update codes according 
to your suggestion

On 2015/8/25 21:12, Yasuaki Ishimatsu wrote:
> On Thu, 20 Aug 2015 03:28:05 -0400
> Changsheng Liu <liuchangsheng@xxxxxxxxxx> wrote:
>
> > From: Changsheng Liu <liuchangcheng@xxxxxxxxxx>
> >
> > When memory is hot added, should_add_memory_movable() always returns 0
> > because the movable zone is empty, so the memory that was hot added will
> > add to the normal zone even if we want to remove the memory.
> >
> > So we change should_add_memory_movable(): if the user config
> > CONFIG_MOVABLE_NODE it will return 1 when the movable zone is empty.
> >
> > Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Changsheng Liu <liuchangcheng@xxxxxxxxxx>
> > Tested-by: Dongdong Fan <fandd@xxxxxxxxxx>
> > ---
> >   mm/memory_hotplug.c |    3 +--
> >   1 files changed, 1 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 26fbba7..ff658f2 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1199,8 +1199,7 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
> >   	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
> >   
> >   	if (zone_is_empty(movable_zone))
> > -		return 0;
> > -
> > +		return IS_ENABLED(CONFIG_MOVABLE_NODE);
> >   	if (movable_zone->zone_start_pfn <= start_pfn)
> >   		return 1;
> Currently, kernel allows to create ZONE_MOVABLE after ZONE_NORMAL as follows:
>   PFN low                                 high
>         ---|-------------|-------------|---
>              ZONE_NORMAL   ZONE_MOVABLE
>
> But kernel does not allow to create ZONE_MOVABLE before ZONE_NORMAL as follows:
>   PFN low                                 high
>         ---|-------------|-------------|---
>              ZONE_MOVABLE  ZONE_NORMAL
>
> Also, kernel does not allow to create ZONE_MOVABLE in ZOME_NORMAL as follows:
>   PFN low                                              high
>         ---|-------------|-------------|-------------|---
>              ZONE_NORMAL   ZONE_MOVABLE  ZONE_NORMAL
>
> So should_add_memory_movable() checks them.
>
> Accoring to your patch, when movable_zone is empty, the hot added memory is
> always managed to ZONE_MOVABLE. It means that ZONE_MOVALBE will puts before/in
> ZONE_NORMAL.
>
> You must prevent from creating ZONE_MOVABLE before/in ZONE_NORMAL.
>
> Thanks,
> Yasuaki Ishimatsu
>
> >   
> > --
> > 1.7.1
> >
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