| Message ID | 20181119101616.8901-2-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v1,1/8] mm: balloon: update comment about isolation/migration/compaction | expand |
On Mon, Nov 19, 2018 at 11:16:09AM +0100, David Hildenbrand wrote: > Commit b1123ea6d3b3 ("mm: balloon: use general non-lru movable page > feature") reworked balloon handling to make use of the general > non-lru movable page feature. The big comment block in > balloon_compaction.h contains quite some outdated information. Let's fix > this. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Michal Hocko <mhocko@suse.com> > Cc: "Michael S. Tsirkin" <mst@redhat.com> > Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> > --- > include/linux/balloon_compaction.h | 26 +++++++++----------------- > 1 file changed, 9 insertions(+), 17 deletions(-) > > diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h > index 53051f3d8f25..cbe50da5a59d 100644 > --- a/include/linux/balloon_compaction.h > +++ b/include/linux/balloon_compaction.h > @@ -4,15 +4,18 @@ > * > * Common interface definitions for making balloon pages movable by compaction. > * > - * Despite being perfectly possible to perform ballooned pages migration, they > - * make a special corner case to compaction scans because balloon pages are not > - * enlisted at any LRU list like the other pages we do compact / migrate. > + * Balloon page migration makes use of the general non-lru movable page > + * 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. > * > * 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 > * performing balloon page compaction. In order to sort out these racy scenarios > * and safely perform balloon's page compaction and migration we must, always, > - * ensure following these three simple rules: > + * 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 > @@ -21,19 +24,8 @@ > * +--spin_lock_irq(&b_dev_info->pages_lock); > * ... page->mapping updates here ... > * > - * ii. before isolating or dequeueing a balloon page from the balloon device > - * pages list, the page reference counter must be raised by one and the > - * extra refcount must be dropped when the page is enqueued back into > - * the balloon device page list, thus a balloon page keeps its reference > - * 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 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. > + * ii. isolation or dequeueing procedure must remove the page from balloon > + * device page list under b_dev_info->pages_lock. > * > * 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 > -- > 2.17.2
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index 53051f3d8f25..cbe50da5a59d 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -4,15 +4,18 @@ * * Common interface definitions for making balloon pages movable by compaction. * - * Despite being perfectly possible to perform ballooned pages migration, they - * make a special corner case to compaction scans because balloon pages are not - * enlisted at any LRU list like the other pages we do compact / migrate. + * Balloon page migration makes use of the general non-lru movable page + * 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. * * 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 * performing balloon page compaction. In order to sort out these racy scenarios * and safely perform balloon's page compaction and migration we must, always, - * ensure following these three simple rules: + * 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 @@ -21,19 +24,8 @@ * +--spin_lock_irq(&b_dev_info->pages_lock); * ... page->mapping updates here ... * - * ii. before isolating or dequeueing a balloon page from the balloon device - * pages list, the page reference counter must be raised by one and the - * extra refcount must be dropped when the page is enqueued back into - * the balloon device page list, thus a balloon page keeps its reference - * 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 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. + * ii. isolation or dequeueing procedure must remove the page from balloon + * device page list under b_dev_info->pages_lock. * * 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
Commit b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature") reworked balloon handling to make use of the general non-lru movable page feature. The big comment block in balloon_compaction.h contains quite some outdated information. Let's fix this. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/balloon_compaction.h | 26 +++++++++----------------- 1 file changed, 9 insertions(+), 17 deletions(-)