On Wed, 18 Jul 2012 20:07:07 -0300
Rafael Aquini <aqu...@redhat.com> wrote:
> >
> > > +}
> > > +#else
> > > +static inline bool is_balloon_page(struct page *page) { return
> > > false; }
> > > +static inline bool isolate_balloon_page(struct page *page) { return
> > > false; }
> > > +static inline bool putback_balloon_page(struct page *page) { return
> > > false; }
> > > +#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && COMPACTION */
> >
> > This means that if CONFIG_VIRTIO_BALLOON=y and CONFIG_COMPACTION=n,
> > is_balloon_page() will always return NULL. IOW, no pages are balloon
> > pages! This is wrong.
> >
> I believe it's right, actually, as we can see CONFIG_COMPACTION=n associated
> with
> CONFIG_MIGRATION=y (and CONFIG_VIRTIO_BALLOON=y).
> For such config case we cannot perform the is_balloon_page() test branches
> placed on mm/migration.c
No, it isn't right. Look at the name: "is_balloon_page". If a caller
runs is_balloon_page() against a balloon page with CONFIG_COMPACTION=n
then they will get "false", which is incorrect.
So the function needs a better name - one which communicates that it is
a balloon page *for the purposes of processing by the compaction code*.
Making the function private to compaction.c would help with that, if
feasible.
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