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Date: Mon, 25 Jun 2012 20:57:40 -0300
From: Rafael Aquini <aquini@...hat.com>
To: Konrad Rzeszutek Wilk <konrad@...nok.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Rusty Russell <rusty@...tcorp.com.au>,
"Michael S. Tsirkin" <mst@...hat.com>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 1/4] mm: introduce compaction and migration for virtio
ballooned pages
On Mon, Jun 25, 2012 at 07:31:38PM -0400, Konrad Rzeszutek Wilk wrote:
> On Mon, Jun 25, 2012 at 7:25 PM, Rafael Aquini <aquini@...hat.com> wrote:
> > This patch introduces helper functions that teach compaction and migration bits
> > how to cope with pages which are part of a guest memory balloon, in order to
> > make them movable by memory compaction procedures.
> >
>
> Should the names that are exported be prefixed with kvm_?
>
I rather let them as generic as possible, specially because I believe other
balloon drivers can leverage the same technique to make their page lists movable
as well, in the near future. However, I do agree with your tip if we ended up
finding out no one else can reuse this piece of code.
> > Signed-off-by: Rafael Aquini <aquini@...hat.com>
> > ---
> > include/linux/mm.h | 17 +++++++++++++
> > mm/compaction.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > mm/migrate.c | 30 +++++++++++++++++++++-
> > 3 files changed, 118 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index b36d08c..360656e 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1629,5 +1629,22 @@ static inline unsigned int debug_guardpage_minorder(void) { return 0; }
> > static inline bool page_is_guard(struct page *page) { return false; }
> > #endif /* CONFIG_DEBUG_PAGEALLOC */
> >
> > +#if (defined(CONFIG_VIRTIO_BALLOON) || \
> > + defined(CONFIG_VIRTIO_BALLOON_MODULE)) && defined(CONFIG_COMPACTION)
> > +extern int is_balloon_page(struct page *);
> > +extern int isolate_balloon_page(struct page *);
> > +extern int putback_balloon_page(struct page *);
> > +
> > +/* return 1 if page is part of a guest's memory balloon, 0 otherwise */
> > +static inline int PageBalloon(struct page *page)
> > +{
> > + return is_balloon_page(page);
> > +}
> > +#else
> > +static inline int PageBalloon(struct page *page) { return 0; }
> > +static inline int isolate_balloon_page(struct page *page) { return 0; }
> > +static inline int putback_balloon_page(struct page *page) { return 0; }
> > +#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && COMPACTION */
> > +
> > #endif /* __KERNEL__ */
> > #endif /* _LINUX_MM_H */
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 7ea259d..8835d55 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -14,6 +14,7 @@
> > #include <linux/backing-dev.h>
> > #include <linux/sysctl.h>
> > #include <linux/sysfs.h>
> > +#include <linux/export.h>
> > #include "internal.h"
> >
> > #if defined CONFIG_COMPACTION || defined CONFIG_CMA
> > @@ -312,6 +313,14 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> > continue;
> > }
> >
> > + /*
> > + * For ballooned pages, we need to isolate them before testing
> > + * for PageLRU, as well as skip the LRU page isolation steps.
> > + */
> > + if (PageBalloon(page))
> > + if (isolate_balloon_page(page))
> > + goto isolated_balloon_page;
> > +
> > if (!PageLRU(page))
> > continue;
> >
> > @@ -338,6 +347,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> >
> > /* Successfully isolated */
> > del_page_from_lru_list(page, lruvec, page_lru(page));
> > +isolated_balloon_page:
> > list_add(&page->lru, migratelist);
> > cc->nr_migratepages++;
> > nr_isolated++;
> > @@ -903,4 +913,66 @@ void compaction_unregister_node(struct node *node)
> > }
> > #endif /* CONFIG_SYSFS && CONFIG_NUMA */
> >
> > +#if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)
> > +/*
> > + * Balloon pages special page->mapping.
> > + * users must properly allocate and initiliaze an instance of balloon_mapping,
> > + * and set it as the page->mapping for balloon enlisted page instances.
> > + *
> > + * address_space_operations necessary methods for ballooned pages:
> > + * .migratepage - used to perform balloon's page migration (as is)
> > + * .invalidatepage - used to isolate a page from balloon's page list
> > + * .freepage - used to reinsert an isolated page to balloon's page list
> > + */
> > +struct address_space *balloon_mapping;
> > +EXPORT_SYMBOL(balloon_mapping);
> > +
> > +/* ballooned page id check */
> > +int is_balloon_page(struct page *page)
> > +{
> > + struct address_space *mapping = page->mapping;
> > + if (mapping == balloon_mapping)
> > + return 1;
> > + return 0;
> > +}
> > +
> > +/* __isolate_lru_page() counterpart for a ballooned page */
> > +int isolate_balloon_page(struct page *page)
> > +{
> > + struct address_space *mapping = page->mapping;
> > + if (mapping->a_ops->invalidatepage) {
> > + /*
> > + * We can race against move_to_new_page() and stumble across a
> > + * locked 'newpage'. If we succeed on isolating it, the result
> > + * tends to be disastrous. So, we sanely skip PageLocked here.
> > + */
> > + if (likely(!PageLocked(page) && get_page_unless_zero(page))) {
> > + /*
> > + * A ballooned page, by default, has just one refcount.
> > + * Prevent concurrent compaction threads from isolating
> > + * an already isolated balloon page.
> > + */
> > + if (page_count(page) == 2) {
> > + mapping->a_ops->invalidatepage(page, 0);
> > + return 1;
> > + }
> > + /* Drop refcount taken for this already isolated page */
> > + put_page(page);
> > + }
> > + }
> > + return 0;
> > +}
> > +
> > +/* putback_lru_page() counterpart for a ballooned page */
> > +int putback_balloon_page(struct page *page)
> > +{
> > + struct address_space *mapping = page->mapping;
> > + if (mapping->a_ops->freepage) {
> > + mapping->a_ops->freepage(page);
> > + put_page(page);
> > + return 1;
> > + }
> > + return 0;
> > +}
> > +#endif /* CONFIG_VIRTIO_BALLOON || CONFIG_VIRTIO_BALLOON_MODULE */
> > #endif /* CONFIG_COMPACTION */
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index be26d5c..ffc02a4 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -78,7 +78,10 @@ void putback_lru_pages(struct list_head *l)
> > list_del(&page->lru);
> > dec_zone_page_state(page, NR_ISOLATED_ANON +
> > page_is_file_cache(page));
> > - putback_lru_page(page);
> > + if (unlikely(PageBalloon(page)))
> > + VM_BUG_ON(!putback_balloon_page(page));
> > + else
> > + putback_lru_page(page);
> > }
> > }
> >
> > @@ -783,6 +786,17 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> > }
> > }
> >
> > + if (PageBalloon(page)) {
> > + /*
> > + * A ballooned page does not need any special attention from
> > + * physical to virtual reverse mapping procedures.
> > + * To avoid burning cycles at rmap level,
> > + * skip attempts to unmap PTEs or remap swapcache.
> > + */
> > + remap_swapcache = 0;
> > + goto skip_unmap;
> > + }
> > +
> > /*
> > * Corner case handling:
> > * 1. When a new swap-cache page is read into, it is added to the LRU
> > @@ -852,6 +866,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> > goto out;
> >
> > rc = __unmap_and_move(page, newpage, force, offlining, mode);
> > +
> > + if (PageBalloon(newpage)) {
> > + /*
> > + * A ballooned page has been migrated already. Now, it is the
> > + * time to wrap-up counters, handle the old page back to Buddy
> > + * and return.
> > + */
> > + list_del(&page->lru);
> > + dec_zone_page_state(page, NR_ISOLATED_ANON +
> > + page_is_file_cache(page));
> > + put_page(page);
> > + __free_page(page);
> > + return rc;
> > + }
> > out:
> > if (rc != -EAGAIN) {
> > /*
> > --
> > 1.7.10.2
> >
> > --
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> > the body to majordomo@...ck.org. For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
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> >
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