On Tue, 2011-03-08 at 22:50 +0100, Daniel Kiper wrote:
> +static enum bp_state reserve_additional_memory(long credit)
> +{
> + int rc;
> + unsigned long balloon_hotplug = credit;
> +
> + balloon_hotplug <<= PAGE_SHIFT;
> +
> + rc = add_virtual_memory((u64 *)&balloon_hotplug);
This would work if all 'unsigned long's were 64-bits. It'll break on
32-bit kernels in a very bad way by overwriting 4 bytes of stack.
> + if (rc) {
> + pr_info("xen_balloon: %s: add_virtual_memory() failed: %i\n", __func__, rc);
> + return BP_EAGAIN;
> + }
> +
> + balloon_hotplug >>= PAGE_SHIFT;
> +
> + balloon_hotplug -= credit;
> +
> + balloon_stats.hotplug_pages += credit;
> + balloon_stats.balloon_hotplug = balloon_hotplug;
> +
> + return BP_DONE;
> +}
> +
> +static int xen_online_page_notifier(struct notifier_block *nb, unsigned long val, void *v)
> +{
> + struct page *page = v;
> + unsigned long pfn = page_to_pfn(page);
> +
> + if (pfn >= num_physpages)
> + num_physpages = pfn + 1;
> +
> + inc_totalhigh_pages();
> +
> +#ifdef CONFIG_FLATMEM
> + max_mapnr = max(pfn, max_mapnr);
> +#endif
I really don't like that this is a direct copy of online_page() up to
this point. They're already subtly different. I'm also curious if this
breaks on 32-bit kernels because of the unconditional
inc_totalhigh_pages().
If it's done this way, I'd almost guarantee that the first time someone
fixes a bug or adds a generic feature in online_page() that Xen gets
missed.
> + mutex_lock(&balloon_mutex);
> +
> + __balloon_append(page);
> +
> + if (balloon_stats.hotplug_pages)
> + --balloon_stats.hotplug_pages;
> + else
> + --balloon_stats.balloon_hotplug;
> +
> + mutex_unlock(&balloon_mutex);
> +
> + return NOTIFY_STOP;
> +}
I'm not a _huge_ fan of these notifier chains, but I guess it works.
However, if you're going to use these notifier chains, then we probably
should use them to full effect. Have a notifier list like this:
1. generic online_page()
2. xen_online_page_notifier() (returns NOTIFY_STOP)
3. free_online_page()
Where finish_online_page() does something like this:
finish_online_page(...)
{
ClearPageReserved(page);
init_page_count(page);
__free_page(page);
}
These patches are definitely getting there. Just another round or two,
and they should be ready to go.
-- Dave
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