Re: [RFC PATCH 10/12] mm: add the buddy system interface

[Kamezawa Hiroyuki]

On 2015/06/16 2:20, Luck, Tony wrote:
> On Mon, Jun 15, 2015 at 05:47:27PM +0900, Kamezawa Hiroyuki wrote:
> > So, there are 3 ideas.
> >
> >   (1) kernel only from MIRROR / user only from MOVABLE (Tony)
> >   (2) kernel only from MIRROR / user from MOVABLE + MIRROR(ASAP)  (AKPM suggested)
> >       This makes use of the fact MOVABLE memory is reclaimable but Tony pointed out
> >       the memory reclaim can be critical for GFP_ATOMIC.
> >   (3) kernel only from MIRROR / user from MOVABLE, special user from MIRROR (Xishi)
> >
> > 2 Implementation ideas.
> >    - creating ZONE
> >    - creating new alloation attribute
> >
> > I don't convince whether we need some new structure in mm. Isn't it good to use
> > ZONE_MOVABLE for not-mirrored memory ?
> > Then, disable fallback from ZONE_MOVABLE -> ZONE_NORMAL for (1) and (3)
>
> We might need to rename it ... right now the memory hotplug
> people use ZONE_MOVABLE to indicate regions of physical memory
> that can be removed from the system.  I'm wondering whether
> people will want systems that have both removable and mirrored
> areas?  Then we have four attribute combinations:
>
> mirror=no  removable=no  - prefer to use for user, could use for kernel if we run out of mirror
> mirror=no  removable=yes - can only be used for user (kernel allocation makes it not-removable)
> mirror=yes removable=no  - use for kernel, possibly for special users if we define some interface
> mirror=yes removable=yes - must not use for kernel ... would have to give to user ... seems like a bad idea to configure a system this way

Thank you for clarification. I see "mirror=no, removable=no" case may require a new name.

IMHO, the value of Address-Based-Memory-Mirror is that users can protect their system's
important functions without using full-memory mirror. So, I feel thinking
"mirror=no, removable=no" just makes our discussion/implemenation complex without real
user value.

Shouldn't we start with just thiking 2 cases of
 mirror=no  removable=yes
 mirror=yes removable=no
?

And then, if the naming is problem, alias name can be added.

Thanks,
-Kame






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