[libvirt] [PATCH v2 3/7] virnuma: Introduce pages helpers

[Daniel P. Berrange]

On Thu, Jun 19, 2014 at 12:06:44PM +0100, Daniel P. Berrange wrote:
> On Mon, Jun 16, 2014 at 05:08:26PM +0200, Michal Privoznik wrote:
> > +int
> > +virNumaGetPageInfo(int node,
> > +                   unsigned int page_size,
> > +                   unsigned int *page_avail,
> > +                   unsigned int *page_free)
> > +{
> > +    int ret = -1;
> > +    long system_page_size = sysconf(_SC_PAGESIZE);
> > +
> > +    /* sysconf() returns page size in bytes,
> > +     * the @page_size is however in kibibytes */
> > +    if (page_size == system_page_size / 1024) {
> > +        unsigned long long memsize, memfree;
> > +
> > +        /* TODO: come up with better algorithm that takes huge pages into
> > +         * account. The problem is huge pages cut off regular memory. */
> 
> Hmm, so this code is returning normal page count that ignores the fact
> that some pages are not in fact usable because they've been stolen for
> huge pages ? I was thinking that the total memory reported by the kernel
> was reduced when you allocated huage pages, but testing now, it seems I
> was mistaken in that belief.  So this is a bit of a nasty gotcha because
> a user of this API would probably expect that the sum of page size *
> page count for all page sizes would equal total physical RAM (give or
> take).
> 
> I still like the idea of including the default page size in this info,
> but perhaps we should disable the default system page size for now &
> revisit later if we can figure out a way to accurately report it,
> rather than reporting misleading info.

I should have said, ACK to either #ifdef 0 system page size or ACK to
your previous version of this patch, unless someone has better ideas
to accurately report total + free info for default page sizes.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|