Let's bring the docs up-to-date. Setting PG_movable_ops + page->private very likely still requires to be performed under documented locks: it's complicated.
We will rework this in the future, as we will try avoiding using the page lock. Signed-off-by: David Hildenbrand <da...@redhat.com> --- include/linux/balloon_compaction.h | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index b222b0737c466..2fecfead91d26 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -4,12 +4,13 @@ * * Common interface definitions for making balloon pages movable by compaction. * - * Balloon page migration makes use of the general non-lru movable page + * Balloon page migration makes use of the general "movable_ops page migration" * feature. * * page->private is used to reference the responsible balloon device. - * page->mapping is used in context of non-lru page migration to reference - * the address space operations for page isolation/migration/compaction. + * That these pages have movable_ops, and which movable_ops apply, + * is derived from the page type (PageOffline()) combined with the + * PG_movable_ops flag (PageMovableOps()). * * As the page isolation scanning step a compaction thread does is a lockless * procedure (from a page standpoint), it might bring some racy situations while @@ -17,12 +18,10 @@ * and safely perform balloon's page compaction and migration we must, always, * ensure following these simple rules: * - * i. when updating a balloon's page ->mapping element, strictly do it under - * the following lock order, independently of the far superior - * locking scheme (lru_lock, balloon_lock): + * i. Setting the PG_movable_ops flag and page->private with the following + * lock order * +-page_lock(page); * +--spin_lock_irq(&b_dev_info->pages_lock); - * ... page->mapping updates here ... * * ii. isolation or dequeueing procedure must remove the page from balloon * device page list under b_dev_info->pages_lock. -- 2.49.0
