diff options
| -rw-r--r-- | drivers/virtio/virtio_balloon.c | 15 | ||||
| -rw-r--r-- | include/linux/balloon_compaction.h | 97 | ||||
| -rw-r--r-- | include/linux/migrate.h | 11 | ||||
| -rw-r--r-- | include/linux/mm.h | 19 | ||||
| -rw-r--r-- | mm/balloon_compaction.c | 26 | ||||
| -rw-r--r-- | mm/compaction.c | 2 | ||||
| -rw-r--r-- | mm/migrate.c | 16 |
7 files changed, 68 insertions, 118 deletions
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 25ebe8e..c3eb93f 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -163,8 +163,8 @@ static void release_pages_by_pfn(const u32 pfns[], unsigned int num) /* Find pfns pointing at start of each page, get pages and free them. */ for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) { struct page *page = balloon_pfn_to_page(pfns[i]); - balloon_page_free(page); adjust_managed_page_count(page, 1); + put_page(page); /* balloon reference */ } } @@ -395,6 +395,8 @@ static int virtballoon_migratepage(struct address_space *mapping, if (!mutex_trylock(&vb->balloon_lock)) return -EAGAIN; + get_page(newpage); /* balloon reference */ + /* balloon's page migration 1st step -- inflate "newpage" */ spin_lock_irqsave(&vb_dev_info->pages_lock, flags); balloon_page_insert(newpage, mapping, &vb_dev_info->pages); @@ -404,12 +406,7 @@ static int virtballoon_migratepage(struct address_space *mapping, set_page_pfns(vb->pfns, newpage); tell_host(vb, vb->inflate_vq); - /* - * balloon's page migration 2nd step -- deflate "page" - * - * It's safe to delete page->lru here because this page is at - * an isolated migration list, and this step is expected to happen here - */ + /* balloon's page migration 2nd step -- deflate "page" */ balloon_page_delete(page); vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; set_page_pfns(vb->pfns, page); @@ -417,7 +414,9 @@ static int virtballoon_migratepage(struct address_space *mapping, mutex_unlock(&vb->balloon_lock); - return MIGRATEPAGE_BALLOON_SUCCESS; + put_page(page); /* balloon reference */ + + return MIGRATEPAGE_SUCCESS; } /* define the balloon_mapping->a_ops callback to allow balloon page migration */ diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index 089743a..38aa07d 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -27,10 +27,13 @@ * counter raised only while it is under our special handling; * * iii. after the lockless scan step have selected a potential balloon page for - * isolation, re-test the page->mapping flags and the page ref counter + * isolation, re-test the PageBalloon mark and the PagePrivate flag * under the proper page lock, to ensure isolating a valid balloon page * (not yet isolated, nor under release procedure) * + * iv. isolation or dequeueing procedure must clear PagePrivate flag under + * page lock together with removing page from balloon device page list. + * * The functions provided by this interface are placed to help on coping with * the aforementioned balloon page corner case, as well as to ensure the simple * set of exposed rules are satisfied while we are dealing with balloon pages @@ -71,28 +74,6 @@ static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info) kfree(b_dev_info); } -/* - * balloon_page_free - release a balloon page back to the page free lists - * @page: ballooned page to be set free - * - * This function must be used to properly set free an isolated/dequeued balloon - * page at the end of a sucessful page migration, or at the balloon driver's - * page release procedure. - */ -static inline void balloon_page_free(struct page *page) -{ - /* - * Balloon pages always get an extra refcount before being isolated - * and before being dequeued to help on sorting out fortuite colisions - * between a thread attempting to isolate and another thread attempting - * to release the very same balloon page. - * - * Before we handle the page back to Buddy, lets drop its extra refcnt. - */ - put_page(page); - __free_page(page); -} - #ifdef CONFIG_BALLOON_COMPACTION extern bool balloon_page_isolate(struct page *page); extern void balloon_page_putback(struct page *page); @@ -108,74 +89,33 @@ static inline void balloon_mapping_free(struct address_space *balloon_mapping) } /* - * page_flags_cleared - helper to perform balloon @page ->flags tests. - * - * As balloon pages are obtained from buddy and we do not play with page->flags - * at driver level (exception made when we get the page lock for compaction), - * we can safely identify a ballooned page by checking if the - * PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared. This approach also - * helps us skip ballooned pages that are locked for compaction or release, thus - * mitigating their racy check at balloon_page_movable() - */ -static inline bool page_flags_cleared(struct page *page) -{ - return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP); -} - -/* - * __is_movable_balloon_page - helper to perform @page mapping->flags tests + * __is_movable_balloon_page - helper to perform @page PageBalloon tests */ static inline bool __is_movable_balloon_page(struct page *page) { - struct address_space *mapping = page->mapping; - return mapping_balloon(mapping); + return PageBalloon(page); } /* - * balloon_page_movable - test page->mapping->flags to identify balloon pages - * that can be moved by compaction/migration. - * - * This function is used at core compaction's page isolation scheme, therefore - * most pages exposed to it are not enlisted as balloon pages and so, to avoid - * undesired side effects like racing against __free_pages(), we cannot afford - * holding the page locked while testing page->mapping->flags here. + * balloon_page_movable - test PageBalloon to identify balloon pages + * and PagePrivate to check that the page is not + * isolated and can be moved by compaction/migration. * * As we might return false positives in the case of a balloon page being just - * released under us, the page->mapping->flags need to be re-tested later, - * under the proper page lock, at the functions that will be coping with the - * balloon page case. + * released under us, this need to be re-tested later, under the page lock. */ static inline bool balloon_page_movable(struct page *page) { - /* - * Before dereferencing and testing mapping->flags, let's make sure - * this is not a page that uses ->mapping in a different way - */ - if (page_flags_cleared(page) && !page_mapped(page) && - page_count(page) == 1) - return __is_movable_balloon_page(page); - - return false; + return PageBalloon(page) && PagePrivate(page); } /* * isolated_balloon_page - identify an isolated balloon page on private * compaction/migration page lists. - * - * After a compaction thread isolates a balloon page for migration, it raises - * the page refcount to prevent concurrent compaction threads from re-isolating - * the same page. For that reason putback_movable_pages(), or other routines - * that need to identify isolated balloon pages on private pagelists, cannot - * rely on balloon_page_movable() to accomplish the task. */ static inline bool isolated_balloon_page(struct page *page) { - /* Already isolated balloon pages, by default, have a raised refcount */ - if (page_flags_cleared(page) && !page_mapped(page) && - page_count(page) >= 2) - return __is_movable_balloon_page(page); - - return false; + return PageBalloon(page); } /* @@ -192,6 +132,8 @@ static inline void balloon_page_insert(struct page *page, struct address_space *mapping, struct list_head *head) { + __SetPageBalloon(page); + SetPagePrivate(page); page->mapping = mapping; list_add(&page->lru, head); } @@ -206,8 +148,12 @@ static inline void balloon_page_insert(struct page *page, */ static inline void balloon_page_delete(struct page *page) { + __ClearPageBalloon(page); page->mapping = NULL; - list_del(&page->lru); + if (PagePrivate(page)) { + ClearPagePrivate(page); + list_del(&page->lru); + } } /* @@ -258,6 +204,11 @@ static inline void balloon_page_delete(struct page *page) list_del(&page->lru); } +static inline bool __is_movable_balloon_page(struct page *page) +{ + return false; +} + static inline bool balloon_page_movable(struct page *page) { return false; diff --git a/include/linux/migrate.h b/include/linux/migrate.h index b66fd10..01aad3e 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -13,18 +13,9 @@ typedef void free_page_t(struct page *page, unsigned long private); * Return values from addresss_space_operations.migratepage(): * - negative errno on page migration failure; * - zero on page migration success; - * - * The balloon page migration introduces this special case where a 'distinct' - * return code is used to flag a successful page migration to unmap_and_move(). - * This approach is necessary because page migration can race against balloon - * deflation procedure, and for such case we could introduce a nasty page leak - * if a successfully migrated balloon page gets released concurrently with - * migration's unmap_and_move() wrap-up steps. */ #define MIGRATEPAGE_SUCCESS 0 -#define MIGRATEPAGE_BALLOON_SUCCESS 1 /* special ret code for balloon page - * sucessful migration case. - */ + enum migrate_reason { MR_COMPACTION, MR_MEMORY_FAILURE, diff --git a/include/linux/mm.h b/include/linux/mm.h index 4d814aa..fa0d74e 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -554,6 +554,25 @@ static inline void __ClearPageBuddy(struct page *page) atomic_set(&page->_mapcount, -1); } +#define PAGE_BALLOON_MAPCOUNT_VALUE (-256) + +static inline int PageBalloon(struct page *page) +{ + return atomic_read(&page->_mapcount) == PAGE_BALLOON_MAPCOUNT_VALUE; +} + +static inline void __SetPageBalloon(struct page *page) +{ + VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page); + atomic_set(&page->_mapcount, PAGE_BALLOON_MAPCOUNT_VALUE); +} + +static inline void __ClearPageBalloon(struct page *page) +{ + VM_BUG_ON_PAGE(!PageBalloon(page), page); + atomic_set(&page->_mapcount, -1); +} + void put_page(struct page *page); void put_pages_list(struct list_head *pages); diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c index 6e45a50..52abeeb 100644 --- a/mm/balloon_compaction.c +++ b/mm/balloon_compaction.c @@ -93,17 +93,12 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) * to be released by the balloon driver. */ if (trylock_page(page)) { + if (!PagePrivate(page)) { + /* raced with isolation */ + unlock_page(page); + continue; + } spin_lock_irqsave(&b_dev_info->pages_lock, flags); - /* - * Raise the page refcount here to prevent any wrong - * attempt to isolate this page, in case of coliding - * with balloon_page_isolate() just after we release - * the page lock. - * - * balloon_page_free() will take care of dropping - * this extra refcount later. - */ - get_page(page); balloon_page_delete(page); spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); unlock_page(page); @@ -187,7 +182,9 @@ static inline void __isolate_balloon_page(struct page *page) { struct balloon_dev_info *b_dev_info = page->mapping->private_data; unsigned long flags; + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + ClearPagePrivate(page); list_del(&page->lru); b_dev_info->isolated_pages++; spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); @@ -197,7 +194,9 @@ static inline void __putback_balloon_page(struct page *page) { struct balloon_dev_info *b_dev_info = page->mapping->private_data; unsigned long flags; + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + SetPagePrivate(page); list_add(&page->lru, &b_dev_info->pages); b_dev_info->isolated_pages--; spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); @@ -235,12 +234,11 @@ bool balloon_page_isolate(struct page *page) */ if (likely(trylock_page(page))) { /* - * A ballooned page, by default, has just one refcount. + * A ballooned page, by default, has PagePrivate set. * Prevent concurrent compaction threads from isolating - * an already isolated balloon page by refcount check. + * an already isolated balloon page by clearing it. */ - if (__is_movable_balloon_page(page) && - page_count(page) == 2) { + if (balloon_page_movable(page)) { __isolate_balloon_page(page); unlock_page(page); return true; diff --git a/mm/compaction.c b/mm/compaction.c index b9972c0..edba18a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -640,7 +640,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, */ if (!PageLRU(page)) { if (unlikely(balloon_page_movable(page))) { - if (locked && balloon_page_isolate(page)) { + if (balloon_page_isolate(page)) { /* Successfully isolated */ goto isolate_success; } diff --git a/mm/migrate.c b/mm/migrate.c index 2740360..0143995 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -876,7 +876,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage, } } - if (unlikely(balloon_page_movable(page))) { + if (unlikely(isolated_balloon_page(page))) { /* * A ballooned page does not need any special attention from * physical to virtual reverse mapping procedures. @@ -955,17 +955,6 @@ static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page, rc = __unmap_and_move(page, newpage, force, mode); - if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) { - /* - * A ballooned page has been migrated already. - * Now, it's the time to wrap-up counters, - * handle the page back to Buddy and return. - */ - dec_zone_page_state(page, NR_ISOLATED_ANON + - page_is_file_cache(page)); - balloon_page_free(page); - return MIGRATEPAGE_SUCCESS; - } out: if (rc != -EAGAIN) { /* @@ -988,6 +977,9 @@ out: if (rc != MIGRATEPAGE_SUCCESS && put_new_page) { ClearPageSwapBacked(newpage); put_new_page(newpage, private); + } else if (unlikely(__is_movable_balloon_page(newpage))) { + /* drop our reference, page already in the balloon */ + put_page(newpage); } else putback_lru_page(newpage); |
