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Message-ID: <65601756-e9ae-4a26-acd4-2dcfe58a7f7f@redhat.com>
Date: Fri, 11 Jul 2025 11:58:43 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, virtualization@...ts.linux.dev,
linux-fsdevel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
Jonathan Corbet <corbet@....net>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
<eperezma@...hat.com>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Zi Yan <ziy@...dia.com>, Matthew Brost <matthew.brost@...el.com>,
Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
Ying Huang <ying.huang@...ux.alibaba.com>,
Alistair Popple <apopple@...dia.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
<vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Minchan Kim <minchan@...nel.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
Jason Gunthorpe <jgg@...pe.ca>, John Hubbard <jhubbard@...dia.com>,
Peter Xu <peterx@...hat.com>, Xu Xin <xu.xin16@....com.cn>,
Chengming Zhou <chengming.zhou@...ux.dev>, Miaohe Lin
<linmiaohe@...wei.com>, Naoya Horiguchi <nao.horiguchi@...il.com>,
Oscar Salvador <osalvador@...e.de>, Rik van Riel <riel@...riel.com>,
Harry Yoo <harry.yoo@...cle.com>, Qi Zheng <zhengqi.arch@...edance.com>,
Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH v2 20/29] mm: convert "movable" flag in page->mapping to a
page flag
On 04.07.25 12:25, David Hildenbrand wrote:
> Instead, let's use a page flag. As the page flag can result in
> false-positives, glue it to the page types for which we
> support/implement movable_ops page migration.
>
> We are reusing PG_uptodate, that is for example used to track file
> system state and does not apply to movable_ops pages. So
> warning in case it is set in page_has_movable_ops() on other page types
> could result in false-positive warnings.
>
> Likely we could set the bit using a non-atomic update: in contrast to
> page->mapping, we could have others trying to update the flags
> concurrently when trying to lock the folio. In
> isolate_movable_ops_page(), we already take care of that by checking if
> the page has movable_ops before locking it. Let's start with the atomic
> variant, we could later switch to the non-atomic variant once we are
> sure other cases are similarly fine. Once we perform the switch, we'll
> have to introduce __SETPAGEFLAG_NOOP().
>
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> include/linux/balloon_compaction.h | 2 +-
> include/linux/migrate.h | 8 -----
> include/linux/page-flags.h | 54 ++++++++++++++++++++++++------
> mm/compaction.c | 6 ----
> mm/zpdesc.h | 2 +-
> 5 files changed, 46 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index a8a1706cc56f3..b222b0737c466 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -92,7 +92,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> struct page *page)
> {
> __SetPageOffline(page);
> - __SetPageMovable(page);
> + SetPageMovableOps(page);
> set_page_private(page, (unsigned long)balloon);
> list_add(&page->lru, &balloon->pages);
> }
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 6aece3f3c8be8..acadd41e0b5cf 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -103,14 +103,6 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
>
> #endif /* CONFIG_MIGRATION */
>
> -#ifdef CONFIG_COMPACTION
> -void __SetPageMovable(struct page *page);
> -#else
> -static inline void __SetPageMovable(struct page *page)
> -{
> -}
> -#endif
> -
> #ifdef CONFIG_NUMA_BALANCING
> int migrate_misplaced_folio_prepare(struct folio *folio,
> struct vm_area_struct *vma, int node);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 4c27ebb689e3c..5f2b570735852 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -170,6 +170,11 @@ enum pageflags {
> /* non-lru isolated movable page */
> PG_isolated = PG_reclaim,
>
> +#ifdef CONFIG_MIGRATION
> + /* this is a movable_ops page (for selected typed pages only) */
> + PG_movable_ops = PG_uptodate,
> +#endif
> +
> /* Only valid for buddy pages. Used to track pages that are reported */
> PG_reported = PG_uptodate,
>
> @@ -698,9 +703,6 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
> * bit; and then folio->mapping points, not to an anon_vma, but to a private
> * structure which KSM associates with that merged page. See ksm.h.
> *
> - * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is used for non-lru movable
> - * page and then folio->mapping points to a struct movable_operations.
> - *
> * Please note that, confusingly, "folio_mapping" refers to the inode
> * address_space which maps the folio from disk; whereas "folio_mapped"
> * refers to user virtual address space into which the folio is mapped.
> @@ -743,13 +745,6 @@ static __always_inline bool PageAnon(const struct page *page)
> {
> return folio_test_anon(page_folio(page));
> }
> -
> -static __always_inline bool page_has_movable_ops(const struct page *page)
> -{
> - return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
> - PAGE_MAPPING_MOVABLE;
> -}
> -
> #ifdef CONFIG_KSM
> /*
> * A KSM page is one of those write-protected "shared pages" or "merged pages"
> @@ -1133,6 +1128,45 @@ bool is_free_buddy_page(const struct page *page);
>
> PAGEFLAG(Isolated, isolated, PF_ANY);
>
> +#ifdef CONFIG_MIGRATION
> +/*
> + * This page is migratable through movable_ops (for selected typed pages
> + * only).
> + *
> + * Page migration of such pages might fail, for example, if the page is
> + * already isolated by somebody else, or if the page is about to get freed.
> + *
> + * While a subsystem might set selected typed pages that support page migration
> + * as being movable through movable_ops, it must never clear this flag.
> + *
> + * This flag is only cleared when the page is freed back to the buddy.
> + *
> + * Only selected page types support this flag (see page_movable_ops()) and
> + * the flag might be used in other context for other pages. Always use
> + * page_has_movable_ops() instead.
> + */
> +TESTPAGEFLAG(MovableOps, movable_ops, PF_NO_TAIL);
> +SETPAGEFLAG(MovableOps, movable_ops, PF_NO_TAIL);
> +#else /* !CONFIG_MIGRATION */
> +TESTPAGEFLAG_FALSE(MovableOps, movable_ops);
> +SETPAGEFLAG_NOOP(MovableOps, movable_ops);
> +#endif /* CONFIG_MIGRATION */
> +
> +/**
> + * page_has_movable_ops - test for a movable_ops page
> + * @page The page to test.
> + *
> + * Test whether this is a movable_ops page. Such pages will stay that
> + * way until freed.
> + *
> + * Returns true if this is a movable_ops page, otherwise false.
> + */
> +static inline bool page_has_movable_ops(const struct page *page)
> +{
> + return PageMovableOps(page) &&
> + (PageOffline(page) || PageZsmalloc(page));
> +}
> +
The following fixup on top:
From 3a52911a299d3328d9fa2aeba00170240795702d Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Fri, 11 Jul 2025 11:57:43 +0200
Subject: [PATCH] fixup: "mm: convert "movable" flag in page->mapping to a page
flag"
We're missing a ":".
Signed-off-by: David Hildenbrand <david@...hat.com>
---
include/linux/page-flags.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 970600d79daca..8e4d6eda8a8d6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1150,7 +1150,7 @@ PAGEFLAG_FALSE(MovableOpsIsolated, movable_ops_isolated);
/**
* page_has_movable_ops - test for a movable_ops page
- * @page The page to test.
+ * @page: The page to test.
*
* Test whether this is a movable_ops page. Such pages will stay that
* way until freed.
--
2.50.1
--
Cheers,
David / dhildenb
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