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Fri, 06 Nov 2026 01:56:15 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-492d7dbb0d4sm2752385f8f.50.2026.11.06.01.56.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Nov 2026 01:56:15 -0800 (PST) Message-ID: Date: Fri, 6 Nov 2026 10:56:11 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm/mmu_gather: flush pending references early before the folio limit To: "David Hildenbrand (Arm)" , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Johannes Weiner , Song Liu , Rik van Riel , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, iommu@lists.linux.dev, Chris Mason , stable@vger.kernel.org References: <20261105-refcount_overflow_stable-v1-0-70b9c655da3e@kernel.org> <20261105-refcount_overflow_stable-v1-3-70b9c655da3e@kernel.org> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261105-refcount_overflow_stable-v1-3-70b9c655da3e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/5/26 2:10 PM, David Hildenbrand (Arm) wrote: > When a task zaps mappings (e.g., MADV_DONTNEED), it can drop the PT lock > and defer dropping the folio references. In the meantime, page faults > can refault pagecache folios, creating more references for the same > folios. > > Let's just request a flush after enqueueing a pagecache folio whose > refcount reached a certain threshold. Start flushing well before new > references are refused, regardless of the caller's privileges. > > This is a temporary measure until we have something better. > > Reported-by: Chris Mason > Fixes: 10ebac4f95e7 ("mm/memory: optimize unmap/zap with PTE-mapped THP") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) LGTM: Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a