linux-kernel - Re: [PATCH] mm: make ref_unless functions unless

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Message-ID: <8D231B3B-C82E-4F71-93B5-8ED272EBBAE0@nvidia.com>
Date: Fri, 06 Feb 2026 10:46:05 -0500
From: Zi Yan <ziy@...dia.com>
To: Gladyshev Ilya <gladyshev.ilya1@...artners.com>
Cc: gorbunov.ivan@...artners.com, artem.kuzin@...wei.com,
 stepanov.anatoly@...wei.com, alexander.grubnikov@...wei.com,
 David Hildenbrand <david@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 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>,
 Harry Yoo <harry.yoo@...cle.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Will Deacon <will@...nel.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: make ref_unless functions unless_zero only

On 6 Feb 2026, at 8:33, Gladyshev Ilya wrote:

> There are no users of (folio/page)_ref_add_unless(page, nr, u) with
> u != 0 [1] and all current users are "internal" for page refcounting API.
> This allows us to safely drop this parameter and reduce function
> semantics to the "unless zero" cases only, which will be optimized in
> the following patch.
>
> If needed, these functions for the u!=0 cases can be trivially
> reintroduced later using the same atomic_add_unless operations as before.
>
> [1]: The last user was dropped in v5.18 kernel, commit 27674ef6c73f
> ("mm: remove the extra ZONE_DEVICE struct page refcount"). There is no
> trace of discussion as to why this cleanup wasn't done earlier.
>
> Co-developed-by: Gorbunov Ivan <gorbunov.ivan@...artners.com>
> Signed-off-by: Gorbunov Ivan <gorbunov.ivan@...artners.com>
> Signed-off-by: Gladyshev Ilya <gladyshev.ilya1@...artners.com>
> Acked-by: David Hildenbrand (Arm) <david@...nel.org>
> ---
>  include/linux/mm.h         |  2 +-
>  include/linux/page-flags.h |  6 +++---
>  include/linux/page_ref.h   | 14 +++++++-------
>  3 files changed, 11 insertions(+), 11 deletions(-)
>
Acked-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi