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Message-ID: <c08d13ba-d199-4a9a-8be2-56074fac3f74@redhat.com>
Date: Mon, 30 Jun 2025 14:07:46 +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 RFC 11/29] mm/migrate: move movable_ops page handling out
of move_to_new_folio()
On 18.06.25 19:39, David Hildenbrand wrote:
> Let's move that handling directly into migrate_folio_move(), so we can
> simplify move_to_new_folio(). While at it, fixup the documentation a
> bit.
>
> Note that unmap_and_move_huge_page() does not care, because it only
> deals with actual folios. (we only support migration of
> individual movable_ops pages)
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> mm/migrate.c | 61 ++++++++++++++++++++++++----------------------------
> 1 file changed, 28 insertions(+), 33 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 456e41dad83a2..db807f9bbf975 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1024,11 +1024,12 @@ static int fallback_migrate_folio(struct address_space *mapping,
> }
>
> /*
> - * Move a page to a newly allocated page
> - * The page is locked and all ptes have been successfully removed.
> + * Move a src folio to a newly allocated dst folio.
> *
> - * The new page will have replaced the old page if this function
> - * is successful.
> + * The src and dst folios are locked and the src folios was unmapped from
> + * the page tables.
> + *
> + * On success, the src folio was replaced by the dst folio.
> *
> * Return value:
> * < 0 - error code
> @@ -1037,34 +1038,30 @@ static int fallback_migrate_folio(struct address_space *mapping,
> static int move_to_new_folio(struct folio *dst, struct folio *src,
> enum migrate_mode mode)
> {
> + struct address_space *mapping = folio_mapping(src);
> int rc = -EAGAIN;
> - bool is_lru = !__folio_test_movable(src);
>
> VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
> VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
>
> - if (likely(is_lru)) {
> - struct address_space *mapping = folio_mapping(src);
> -
> - if (!mapping)
> - rc = migrate_folio(mapping, dst, src, mode);
> - else if (mapping_inaccessible(mapping))
> - rc = -EOPNOTSUPP;
> - else if (mapping->a_ops->migrate_folio)
> - /*
> - * Most folios have a mapping and most filesystems
> - * provide a migrate_folio callback. Anonymous folios
> - * are part of swap space which also has its own
> - * migrate_folio callback. This is the most common path
> - * for page migration.
> - */
> - rc = mapping->a_ops->migrate_folio(mapping, dst, src,
> - mode);
> - else
> - rc = fallback_migrate_folio(mapping, dst, src, mode);
> + if (!mapping)
> + rc = migrate_folio(mapping, dst, src, mode);
> + else if (mapping_inaccessible(mapping))
> + rc = -EOPNOTSUPP;
> + else if (mapping->a_ops->migrate_folio)
> + /*
> + * Most folios have a mapping and most filesystems
> + * provide a migrate_folio callback. Anonymous folios
> + * are part of swap space which also has its own
> + * migrate_folio callback. This is the most common path
> + * for page migration.
> + */
> + rc = mapping->a_ops->migrate_folio(mapping, dst, src,
> + mode);
> + else
> + rc = fallback_migrate_folio(mapping, dst, src, mode);
>
> - if (rc != MIGRATEPAGE_SUCCESS)
> - goto out;
> + if (rc == MIGRATEPAGE_SUCCESS) {
> /*
> * For pagecache folios, src->mapping must be cleared before src
> * is freed. Anonymous folios must stay anonymous until freed.
> @@ -1074,10 +1071,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
>
> if (likely(!folio_is_zone_device(dst)))
> flush_dcache_folio(dst);
> - } else {
> - rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
> }
> -out:
> return rc;
> }
>
> @@ -1328,20 +1322,21 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
> int rc;
> int old_page_state = 0;
> struct anon_vma *anon_vma = NULL;
> - bool is_lru = !__folio_test_movable(src);
> struct list_head *prev;
>
> __migrate_folio_extract(dst, &old_page_state, &anon_vma);
> prev = dst->lru.prev;
> list_del(&dst->lru);
>
> + if (unlikely(__folio_test_movable(src))) {
> + rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
> + goto out_unlock_both;
> + }
> +
I suspect this was the issue I was chasing:
diff --git a/mm/migrate.c b/mm/migrate.c
index 9dd327a63abc5..22c115710d0e2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1330,6 +1330,8 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
if (unlikely(__folio_test_movable(src))) {
rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
+ if (rc)
+ goto out;
goto out_unlock_both;
}
Testing ...
--
Cheers,
David / dhildenb
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