From: "David Hildenbrand (Arm)" <david@kernel.org>
To: "Kiryl Shutsemau (Meta)" <kas@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>, Jan Kara <jack@suse.cz>,
Hugh Dickins <hughd@google.com>,
Christian Brauner <brauner@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Harry Yoo <harry@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
Miaohe Lin <linmiaohe@huawei.com>,
Naoya Horiguchi <nao.horiguchi@gmail.com>,
Oscar Salvador <osalvador@suse.de>,
"Liam R. Howlett" <liam@infradead.org>,
Mike Rapoport <rppt@kernel.org>,
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Brendan Jackman <brendan.jackman@linux.dev>,
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Luis Chamberlain <mcgrof@kernel.org>,
Ilya Gladyshev <ilya.gladyshev@linux.dev>,
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linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev,
kernel-team@meta.com
Subject: Re: [RFC PATCH v2 02/18] splice: don't steal page cache folios
Date: Wed, 4 Nov 2026 17:05:29 +0100 [thread overview]
Message-ID: <af2102a2-206d-4c5e-ba1d-1ef42b2b6338@kernel.org> (raw)
In-Reply-To: <20261104130118.2507513-3-kas@kernel.org>
On 11/4/26 14:00, Kiryl Shutsemau (Meta) wrote:
> From: Linus Torvalds <torvalds@linux-foundation.org>
>
> PG_rcu_free holds back the reuse of a folio's memory until a grace
> period after the folio is freed. A stolen page cache pipe buffer is
> reused without being freed: remove_mapping() takes the folio out of the
> page cache and the caller keeps it. fuse_try_move_folio() puts it into
> a fuse file, where writes change it under a reader that found it before
> the steal.
>
> Drop ->try_steal from page_cache_pipe_buf_ops. fuse_try_move_folio()
> and virtio_console's pipe_to_sg() then copy, as they already do when
> stealing fails. SPLICE_F_MOVE from the page cache into a fuse file or
> a virtio console now copies.
>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [kas: rewrote the changelog]
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> ---
> fs/splice.c | 51 ---------------------------------------------------
Removing code is always nice, even independent of the other changes :)
The description doesn't really describe the impact of this change. I assume a
slowdown of certain workloads (does anybody really care?), and temporary
increased memory consumption (as we keep the pagecache page).
No idea how often stealing actually succeeds ... a bit of history why it was
added in the first place and why we no longer care now would be nice.
--
Cheers,
David
next prev parent reply other threads:[~2026-11-04 16:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-04 13:00 [RFC PATCH v2 00/18] mm: read the page cache without folio references Kiryl Shutsemau (Meta)
2026-11-04 13:00 ` [RFC PATCH v2 01/18] mm: free PG_rcu_free folios only after an RCU grace period Kiryl Shutsemau (Meta)
2026-11-04 13:00 ` [RFC PATCH v2 02/18] splice: don't steal page cache folios Kiryl Shutsemau (Meta)
2026-11-04 16:05 ` David Hildenbrand (Arm) [this message]
2026-11-04 13:00 ` [RFC PATCH v2 03/18] fuse: don't move a folio with PG_rcu_free into a fuse file Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 04/18] mm: count the pages waiting for a grace period Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 05/18] mm: expedite the grace period when a CPU has many deferred frees Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 06/18] mm: free the pages waiting for a grace period before OOM Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 07/18] mm: free the pages waiting for a grace period before isolation fails Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 08/18] mm/compaction: free the migrated folios that wait for a grace period Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 09/18] mm/memory-failure: handle folios with PG_rcu_free Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 10/18] mm: have folio_mark_accessed() return whether the folio is hot Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 11/18] mm/filemap: mark a folio accessed in one place in filemap_read() Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 12/18] mm/filemap: set PG_rcu_free on the folios that reads keep coming back to Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 13/18] mm/filemap: read from the page cache without folio references Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 14/18] mm/filemap: read large folios " Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 15/18] mm/filemap: don't store f_ra.prev_pos for FMODE_RANDOM files Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 16/18] mm/shmem: count accesses to a folio the way filemap_read() does Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 17/18] mm/shmem: read without folio references Kiryl Shutsemau (Meta)
2026-11-04 13:01 ` [RFC PATCH v2 18/18] mm/filemap: add a debugfs switch for lockless page cache reads Kiryl Shutsemau (Meta)
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