On Tue, 2011-03-08 at 16:55 +0000, Daniel De Graaf wrote:
> Pages that have been ballooned are useful for other Xen drivers doing
> grant table actions, because these pages have valid struct page/PFNs but
> have no valid MFN so are available for remapping.
>
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
> drivers/xen/balloon.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++--
> include/xen/balloon.h | 3 ++
> 2 files changed, 61 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index b0a7a92..53deaec 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -116,14 +116,17 @@ static void balloon_append(struct page *page)
> }
>
> /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
> -static struct page *balloon_retrieve(void)
> +static struct page *balloon_retrieve(int prefer_highmem)
bool?
> {
> struct page *page;
>
> if (list_empty(&ballooned_pages))
> return NULL;
>
> - page = list_entry(ballooned_pages.next, struct page, lru);
> + if (prefer_highmem)
> + page = list_entry(ballooned_pages.prev, struct page, lru);
> + else
> + page = list_entry(ballooned_pages.next, struct page, lru);
> list_del(&page->lru);
>
> if (PageHighMem(page)) {
> @@ -198,7 +201,7 @@ static int increase_reservation(unsigned long nr_pages)
> goto out;
>
> for (i = 0; i < rc; i++) {
> - page = balloon_retrieve();
> + page = balloon_retrieve(0);
> BUG_ON(page == NULL);
>
> pfn = page_to_pfn(page);
> @@ -328,6 +331,58 @@ void balloon_set_new_target(unsigned long target)
> }
> EXPORT_SYMBOL_GPL(balloon_set_new_target);
>
> +/**
> + * alloc_xenballooned_pages - get pages that have been ballooned out
> + * @nr_pages: Number of pages to get
> + * @pages: pages returned
> + * @return number of pages retrieved
> + */
> +int alloc_xenballooned_pages(int nr_pages, struct page** pages)
> +{
> + int rv = 0;
> + int alloc_failed = 0;
> + struct page* page;
> + mutex_lock(&balloon_mutex);
> + while (rv < nr_pages) {
> + page = balloon_retrieve(1);
> + if (page) {
> + pages[rv++] = page;
> + } else {
> + if (alloc_failed)
> + break;
> + if (decrease_reservation(nr_pages - rv))
> + alloc_failed = 1;
This loop and the "alloc_failed" thing seems pretty subtle.
If I'm reading correctly then if decrease_reservation didn't manage to
return the number of pages we asked for then we have a few more turns of
the handle to retrieve whatever we can, but we already know it's not
going to be everything we asked for, or decrease_reservation would have
succeeded).
The only caller of this is your 3/3 which just returns what it got and
fails if it didn't get everything it asked for.
At least until we have a second caller which requires otherwise (and I
don't think we will) I think this function should either return all or
nothing and should clean up after itself in the latter case, which saves
the caller a job too.
Ian.
> + }
> + }
> + mutex_unlock(&balloon_mutex);
> + return rv;
> +}
> +EXPORT_SYMBOL(alloc_xenballooned_pages);
> +
> +/**
> + * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
> + * @nr_pages: Number of pages
> + * @pages: pages to return
> + */
> +void free_xenballooned_pages(int nr_pages, struct page** pages)
> +{
> + int i;
> +
> + mutex_lock(&balloon_mutex);
> +
> + for (i = 0; i < nr_pages; i++) {
> + if (pages[i])
> + balloon_append(pages[i]);
> + }
> +
> + /* The balloon may be too large now. Shrink it if needed. */
> + if (current_target() != balloon_stats.current_pages)
> + schedule_work(&balloon_worker);
> +
> + mutex_unlock(&balloon_mutex);
> +}
> +EXPORT_SYMBOL(free_xenballooned_pages);
> +
> static int __init balloon_init(void)
> {
> unsigned long pfn, nr_pages, extra_pfn_end;
> diff --git a/include/xen/balloon.h b/include/xen/balloon.h
> index b2b7c21..72a6927 100644
> --- a/include/xen/balloon.h
> +++ b/include/xen/balloon.h
> @@ -19,3 +19,6 @@ struct balloon_stats {
> extern struct balloon_stats balloon_stats;
>
> void balloon_set_new_target(unsigned long target);
> +
> +int alloc_xenballooned_pages(int nr_pages, struct page** pages);
> +void free_xenballooned_pages(int nr_pages, struct page** pages);
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