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[2003:d8:2f22:1000:d72d:fd5f:4118:c70b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38bf3275622sm10534150f8f.69.2025.01.20.04.54.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 04:54:15 -0800 (PST) Message-ID: <37375ace-5601-4d6c-9dac-d1c8268698e9@redhat.com> Date: Mon, 20 Jan 2025 13:54:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 00/11] khugepaged: mTHP support To: Nico Pache , Ryan Roberts Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, aarcange@redhat.com, raquini@redhat.com, dev.jain@arm.com, sunnanyong@huawei.com, usamaarif642@gmail.com, audra@redhat.com, akpm@linux-foundation.org References: <20250108233128.14484-1-npache@redhat.com> <40a65c5e-af98-45f9-a254-7e054b44dc95@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 38AD01C000B X-Stat-Signature: c4jk77udihgkd16qmxizgmrkfhs1tep3 X-HE-Tag: 1737377662-473127 X-HE-Meta: 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 YPvPEId0 9CXi/oKe7hz2Y+xd3NiACFKriLfWNrLBgm75uY5kgLapBIYeUsR7NKd5872xQwHs3SLvp1yZLjzfO69KkCZX0kHuy22QMC4AHhf0rrNpt8l2oMcRsSzTsWnC2rcdQsZnHtq4W9b70uz6V0R99c4l+GRiv08EEHHULIJ6N3VuHAKaBwtMvbzHcYBgWfKkMjBjheiSAlPskiTBiHFfV49VuDtDFjwnVlGcAXo/6e/MF5BGD8EO5AEn2+zPgEGhCtraM/cv1P3HwkS84HbYdfIByTM3BuNBLT9HpqwaYBYJXVzNCn3132U6sJEY9L+C973dGqkTV04cIolO7mWiP0mBPqB4IdUwT/MkEu3ZTm6XhY6YxPpu+TsAYp6Zb4qNHhZGv1x+49OMjf5cJTilPc9bmfYyL2B6GFAck8HvnieIQUzitWD+durz4xejafgOoQHyUmakbp3dFO7U43V6AeGIoY6+Zvw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> I think the 1 problem that emerged during review of Dev's series, which we don't >> have a proper solution to yet, is the issue of "creep", where regions can be >> collapsed to progressively higher orders through iterative scans. At each >> collapse, the required thresholds (e.g. max_ptes_none) are met, and the collapse >> effectively adds more non-none ptes so the next scan will then collapse to even >> higher order. Does your solution suffer from this (theoretical/edge case) issue? >> If not, how did you solve? > > Yes sadly it suffers from the same issue. bringing max_ptes_none much > lower as a default would "help". Can we just keep it simple and only support max_ptes_none = 511 ("pagefault behavior" -- PMD_NR_PAGES - 1) or max_ptes_none = 0 ("deferred behavior") and document that the other weird configurations will make mTHP skip, because "weird and unexpetced" ? :) -- Cheers, David / dhildenb