[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 1/8] mm: balloon: update comment about isolation/migration/compaction
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 balloon_compaction.h contains quite some outdated information.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@xxxxxxxxxxxxxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > --- > 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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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