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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vzwO3-00000007pkc-0XaG; Tue, 10 Mar 2026 12:40:35 +0000 Date: Tue, 10 Mar 2026 12:40:34 +0000 From: Matthew Wilcox To: Dev Jain Cc: "David Hildenbrand (Arm)" , "Lorenzo Stoakes (Oracle)" , akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, ziy@nvidia.com, kas@kernel.org, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH 1/9] mm/rmap: make nr_pages signed in try_to_unmap_one Message-ID: References: <20260310073013.4069309-1-dev.jain@arm.com> <20260310073013.4069309-2-dev.jain@arm.com> <21801fb7-0f42-4ad3-8b85-2ac6013b8aa5@lucifer.local> <31f93292-3de6-475c-b7fe-82ef41a3a7de@kernel.org> <04a7465b-ee69-479f-aaa4-ccdf3ae16805@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <04a7465b-ee69-479f-aaa4-ccdf3ae16805@arm.com> X-Rspam-User: X-Rspamd-Queue-Id: 7550B4000A X-Rspamd-Server: rspam08 X-Stat-Signature: 56sxjmj353fd1e7xmrptq4hat779tu6m X-HE-Tag: 1773146471-594520 X-HE-Meta: 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 Nsp8Apko q+9KaTfsiHdKlcG20PvhEBBiBvrPRE0wtJAVeet645EmEOFB7NrKxvxuWn0N9OX247saCDwQ5jCyht1DQ4SGCcKi4vYiE3uTnSuVYddlssrG/t2pMm/C2G4/2hb7cGLQHO/Icvbe+pPOAutw9QsXkJcrFhGmMKEdj53UXr+xG/nWMROPeRoN3e1or3KABt5uXsfq2IspTEBBiGXnp2vP3NElLyYrkfMop/HGY1Twp1uIoutdi5o1HogT0kfWeZn0u68cIwFILUdLpcoyZfDfE0cpqkQ86jfTDBydPKTC7oCHJ56g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 10, 2026 at 01:53:21PM +0530, Dev Jain wrote: > So when I was playing around with the code, I noticed that passing > unsigned int nr_pages to add_mm_counter(-nr_pages) messes up things. Then Using int (whether signed or unsigned) to store nr_pages is a bad idea. Look how many people are asking about supporting PUD-sized folios. On an ARM 64k PAGE_SIZE machine, that's 2^26 pages which is uncomfortably close to 2^32. It'll only take one more level to exceed that, so, what, five to ten more years? Just use unsigned long everywhere now and save ourselves the grief later.