On Mon, Jan 03, 2011 at 02:33:22PM -0800, Dave Hansen wrote:
> On Wed, 2010-12-29 at 18:07 +0100, Daniel Kiper wrote:
> > +config XEN_BALLOON_MEMORY_HOTPLUG
> > + bool "Xen memory balloon driver with memory hotplug support"
> > + default n
> > + depends on XEN_BALLOON && MEMORY_HOTPLUG
> > + help
> > + Xen memory balloon driver with memory hotplug support allows expanding
> > + memory available for the system above limit declared at system startup.
> > + It is very useful on critical systems which require long run without
> > + rebooting.
>
> This might be better phrased as "Memory hotplug support for Xen balloon
> driver". It might otherwise confuse people about whether they're seeing
> some kind of choice or an _enhancement_ to the existing driver.
Thx. Done. I will send new patch release today.
> Also, why bother even making this a config option? What are the
> downsides if it was always compiled in? You could even make it a
> non-prompting Kconfig option and just automatically turn it on with
> XEN_BALLOON && MEMORY_HOTPLUG.
At this stage of development I think it is better to leave this
as an option for user. Later when this future will be mature it could
be removed. However, I realized that this solution does not give
possibility for user to disable this future at runtime. Maybe
it shoudl be as boot/sysfs option. I am not sure it is required or not.
Currently it is not implemented.
> > +static int allocate_memory_resource(struct resource **r, unsigned long nr_pages)
> > {
> > - unsigned long target = balloon_stats.target_pages;
> > + int rc;
> > + resource_size_t r_min, r_size;
> > +
> > + /*
> > + * Look for first unused memory region starting at page
> > + * boundary. Skip last memory section created at boot time
> > + * becuase it may contains unused memory pages with PG_reserved
> > + * bit not set (online_pages require PG_reserved bit set).
> > + */
> > +
> > + *r = kzalloc(sizeof(struct resource), GFP_KERNEL);
> >
> > - target = min(target,
> > - balloon_stats.current_pages +
> > - balloon_stats.balloon_low +
> > - balloon_stats.balloon_high);
> > + if (!*r)
> > + return -ENOMEM;
> >
> > - return target;
> > + (*r)->name = "System RAM";
> > + (*r)->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> > + r_min = PFN_PHYS(section_nr_to_pfn(pfn_to_section_nr(balloon_stats.boot_max_pfn) + 1));
> > + r_size = nr_pages << PAGE_SHIFT;
> > +
> > + rc = allocate_resource(&iomem_resource, *r, r_size, r_min,
> > + ULONG_MAX, PAGE_SIZE, NULL, NULL);
> > +
> > + if (rc < 0) {
> > + kfree(*r);
> > + *r = NULL;
> > + }
> > +
> > + return rc;
> > }
>
> The double-pointer stuff here ends up looking a little funky. Is there
> any reason you don't just use ERR_PTRs? That might look a bit more
> sane.
After another review I removed all double-pointer stuff (it was
very simple, however, if I read many times code written by myself
it was very difficult to discover that). Now I think it is much better.
Thanks.
> > +static void adjust_memory_resource(struct resource **r, unsigned long nr_pages)
> > +{
> > + if ((*r)->end + 1 - (nr_pages << PAGE_SHIFT) == (*r)->start) {
> > + BUG_ON(release_resource(*r) < 0);
>
> In some kernels, people do:
>
> #define BUG_ON(...) do{}while(0)
>
> to save space. If anyone ever does that with this code, it'll break
> horribly. It's also hard to read these. So, please break logic actions
> _out_ of the BUG_ON() arguments.
>
> That's repeated in quite a few places in here. Make sure to go get them
> all.
Done.
> It also isn't evident what this patch set is trying to do until you get
> down to this 7/7 patch. You might want to put a more complete
> description in 0/7.
Will be done. :-))) Thank you for your help.
Daniel
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