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[71.191.145.202]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-91f23d5f3e4sm50436436d6.16.2026.11.14.12.25.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 12:25:49 -0800 (PST) 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Subject: Re: [PATCH 2/2] mm/mempolicy: limit shared policy ranges per inode From: "Gregory Price (Meta)" To: "David Hildenbrand (Arm)" Cc: "Gregory Price (Meta)" , Hugh Dickins , Baolin Wang , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org In-Reply-To: <70740a32-92f5-4425-8676-68863f3e44c3@kernel.org> References: <20261113-mempolicy_limit-v1-0-16688b2644dc@kernel.org> <20261113-mempolicy_limit-v1-2-16688b2644dc@kernel.org> <179467808112.482102.13365594235443107281.b4-reply@b4> <70740a32-92f5-4425-8676-68863f3e44c3@kernel.org> Date: Sat, 14 Nov 2026 15:25:48 -0500 Message-Id: <179468794889.482102.14066028910704780583.b4-reply@b4> X-Mailer: b4 0.17-dev On 2026-11-14 21:16 +0100, David Hildenbrand (Arm) wrote: > On 11/14/26 18:41, Gregory Price (Meta) wrote: > > > > Multi-task mappers were previously unlimited, but that seems like more > > of a nasty unintended corner case - not a real feature. > > > > A single process is already limited on the number of vmas/policies based > > on `max_map_count`, so it seems natural to just use max_map_count > > directly, but I took a brief look at some distros and most seem to > > ship a raised `max_map_count` (>1 million) by default). > > > > I tested that and even 1 million can cause a soft lockup. > > > > Not sure there's an easy solution here, we might have to rework the shm > > policy locks. > > Do you know a single valid use case that's not solved by patch #1 and would > trigger that many policies? > > Ai was not able to come up with anything for me. Just want to make sure the bases are covered. If others are ok with this change, it doesn't look unreasonable to me. Although I'd wonder whether just using max_map_count's limit instead of adding a new toggle would just be cleaner and avoid adding a new uapi. -- ~Gregory