[PATCH v2 27/29] docs/mm: convert from "Non-LRU page migration" to "movable_ops page migration"
From: David Hildenbrand <hidden>
Date: 2025-07-04 10:26:48
Also in:
linux-doc, linux-fsdevel, linux-mm, lkml, virtualization
Subsystem:
documentation, memory management - misc, the rest · Maintainers:
Jonathan Corbet, Andrew Morton, David Hildenbrand, Linus Torvalds
Let's bring the docs up-to-date. Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Lorenzo Stoakes <redacted> Reviewed-by: Harry Yoo <redacted> Signed-off-by: David Hildenbrand <redacted> --- Documentation/mm/page_migration.rst | 39 ++++++++++++++++++++--------- 1 file changed, 27 insertions(+), 12 deletions(-)
diff --git a/Documentation/mm/page_migration.rst b/Documentation/mm/page_migration.rst
index 519b35a4caf5b..34602b254aa63 100644
--- a/Documentation/mm/page_migration.rst
+++ b/Documentation/mm/page_migration.rst@@ -146,18 +146,33 @@ Steps: 18. The new page is moved to the LRU and can be scanned by the swapper, etc. again. -Non-LRU page migration -====================== - -Although migration originally aimed for reducing the latency of memory -accesses for NUMA, compaction also uses migration to create high-order -pages. For compaction purposes, it is also useful to be able to move -non-LRU pages, such as zsmalloc and virtio-balloon pages. - -If a driver wants to make its pages movable, it should define a struct -movable_operations. It then needs to call __SetPageMovable() on each -page that it may be able to move. This uses the ``page->mapping`` field, -so this field is not available for the driver to use for other purposes. +movable_ops page migration +========================== + +Selected typed, non-folio pages (e.g., pages inflated in a memory balloon, +zsmalloc pages) can be migrated using the movable_ops migration framework. + +The "struct movable_operations" provide callbacks specific to a page type +for isolating, migrating and un-isolating (putback) these pages. + +Once a page is indicated as having movable_ops, that condition must not +change until the page was freed back to the buddy. This includes not +changing/clearing the page type and not changing/clearing the +PG_movable_ops page flag. + +Arbitrary drivers cannot currently make use of this framework, as it +requires: + +(a) a page type +(b) indicating them as possibly having movable_ops in page_has_movable_ops() + based on the page type +(c) returning the movable_ops from page_movable_ops() based on the page + type +(d) not reusing the PG_movable_ops and PG_movable_ops_isolated page flags + for other purposes + +For example, balloon drivers can make use of this framework through the +balloon-compaction infrastructure residing in the core kernel. Monitoring Migration =====================
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2.49.0