From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Kiryl Shutsemau <kas@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@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>, 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>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
Brendan Jackman <brendan.jackman@linux.dev>,
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Ilya Gladyshev <ilya.gladyshev@linux.dev>,
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kernel-team@meta.com
Subject: Re: [RFC PATCH v2 01/18] mm: free PG_rcu_free folios only after an RCU grace period
Date: Thu, 12 Nov 2026 13:32:02 +0100 [thread overview]
Message-ID: <fa90c536-3b3a-417e-a09f-011a12e73048@kernel.org> (raw)
In-Reply-To: <avWv-0LafPyo90ln@thinkstation>
On 11/12/26 13:26, Kiryl Shutsemau wrote:
> On Wed, Nov 11, 2026 at 11:03:38AM +0100, David Hildenbrand (Arm) wrote:
>> So I might be completely off, but what I imagine is that the memdescs will get
>> RCU-freed (these are not pages), and once they are then getting freed, they will
>> probably take the physical page with them.
>>
>> And freeing memdescs through RCU will likely be memdesc specific.
>>
>> I really don't know, Willy might know more about these plans.
>
> Right: once the folio is allocated separately, the lockless read
> dereferences it too, so it has to wait for the grace period along with
> its pages. The per-CPU batching and the waits in the allocator later
> in the series do not depend on where the check sits.
>
> Until then the folio is the struct page, and __free_pages_prepare() is
> the one place every page cache folio passes, so v3 keeps the check
> there.
If we go that way, don't make it effectively folio-centric in the
implementation. That's what triggered my response in the first place.
--
Cheers,
David
next prev parent reply other threads:[~2026-11-12 12:32 UTC|newest]
Thread overview: 46+ 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)
2026-11-05 20:37 ` David Hildenbrand (Arm)
2026-11-06 10:23 ` Kiryl Shutsemau
2026-11-09 14:42 ` David Hildenbrand (Arm)
2026-11-09 15:56 ` Linus Torvalds
2026-11-09 17:23 ` David Hildenbrand (Arm)
2026-11-09 18:01 ` Linus Torvalds
2026-11-11 10:03 ` David Hildenbrand (Arm)
2026-11-12 12:26 ` Kiryl Shutsemau
2026-11-12 12:32 ` David Hildenbrand (Arm) [this message]
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)
2026-11-05 14:55 ` Kiryl Shutsemau
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)
2026-11-09 14:46 ` David Hildenbrand (Arm)
2026-11-09 16:28 ` Linus Torvalds
2026-11-09 16:35 ` Linus Torvalds
2026-11-09 17:48 ` David Hildenbrand (Arm)
2026-11-10 13:58 ` Kiryl Shutsemau
2026-11-04 13:01 ` [RFC PATCH v2 04/18] mm: count the pages waiting for a grace period Kiryl Shutsemau (Meta)
2026-11-09 14:48 ` David Hildenbrand (Arm)
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)
2026-11-05 13:03 ` sashiko-bot
2026-11-12 12:53 ` Kiryl Shutsemau
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)
2026-11-05 13:03 ` sashiko-bot
2026-11-12 14:28 ` Kiryl Shutsemau
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)
2026-11-05 13:03 ` sashiko-bot
2026-11-12 14:46 ` Kiryl Shutsemau
2026-11-04 13:01 ` [RFC PATCH v2 09/18] mm/memory-failure: handle folios with PG_rcu_free Kiryl Shutsemau (Meta)
2026-11-05 13:03 ` sashiko-bot
2026-11-12 14:59 ` Kiryl Shutsemau
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)
2026-11-05 13:03 ` sashiko-bot
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)
2026-11-05 13:03 ` sashiko-bot
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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