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b=QFt9uYJslrjF5lm8zndfOP6s3oryviFzIwtzSew9cvovaEBxxtGMYXzbP6YEwm/FA DzwtNNflGNX7N+8nu1hbd+NJ+jQqOdI3nxhHtvXbWBMjHkTOHLFDSj8QWJTT6IDJYo uFIkB32kYEKxA5/AmPw1FtVZVCuVanyJYv+S67+Bcai0gRX6t533uIfV0YiMDM+DHD mNdELy52vF5rXrxE86yG3e1LrKQK/Q3gpbuAbTkFtthFGJNf334t+hKR6Aw/r/LV6c Q6A7crs20ItQBG5wza5dSlsdlUStwigXBDmsg/3T1ejlnsR3mnSwlXFztAe2aWPAjN 9B/gYwXbsHDkA== Date: Thu, 21 May 2026 15:59:02 +0100 From: Lorenzo Stoakes To: Nico Pache Cc: "David Hildenbrand (Arm)" , Wei Yang , Lance Yang , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v17 04/14] mm/khugepaged: generalize __collapse_huge_page_* for mTHP support Message-ID: References: <20260511185817.686831-5-npache@redhat.com> <20260512074202.10253-1-lance.yang@linux.dev> <20260514031009.f66cgop3ctgiqxz3@master> <9b33339e-157a-45b7-942e-3be3418a5142@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 695FDC0017 X-Stat-Signature: n5mzwdwh6x4drqh1usishkec6xcf7k86 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1779375556-75460 X-HE-Meta: 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 oBq/qyFK v6RrDLeYivgU5g7QiuoQB10TujPtTD9/7aE6XR7a73eulNDZDa8c0wyoD77K4ElfuVncOTvAOWWO6FkIoTIo/0f4khhZ/Pf+leLLILCwhEaKkJkmOiqE333GDgKUspZXdTC1ZVamI4xwnhB2PKmexkgHj/cliFvmNPp3BNBawQiB5t+FHnJns42EaQgzg3lHoA/Y510mCJscAhBF7jQhHFOiFS0mqk8t3AHJgyunqKeBbCSHYTfW4mx0bpm/jcI+ejXLnPVLR3KEuv4j8uc330/rfKWY2gq3LAn0k0oKJKBftedUotp/mwZJtXeVa2KfJMJOLa6sP2Q9k0eFdO4GJT7X1YpKxWTv5rM2eInYRtoef66oQzFtaMfjZofu/UWQ/57L++OJX7iN4cHxp+AfolnqFPnUcF/P6X3KH Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 19, 2026 at 01:05:13PM -0600, Nico Pache wrote: > On Mon, May 18, 2026 at 1:33 PM Lorenzo Stoakes wrote: > > > > On Mon, May 18, 2026 at 03:16:11PM +0200, David Hildenbrand (Arm) wrote: > > > > For me, I would vote for fallback to 0. > > > > > > At this point I'll prefer to not return errors from collapse_max_ptes_none(). > > > It's just rather awkward to return an error deep down in collapse code for a > > > configuration problem. > > > > > > For mthp collapse, we only support max_ptes_none==0 and > > > max_ptes_none=="HPAGE_PMD_NR - 1" (default). > > > > > > If another value is specified while collapsing mTHP, print a warning and treat > > > it as 0 (save value, no creep, no memory waste). > > > > > > In a sense, this is similar to how we handle max_ptes_shared + max_ptes_swap: > > > for mTHP: we always treat them as being 0 for mTHP collapse (and don't issue a > > > warning, because we would issue a warning with the default settings). > > > > > > @Lorenzo, fine with you? > > > > Yes 100%, this sounds sensible both in terms of the error and the default. Let's > > keep our lives simple(-ish) please :) > > Ok thank you im glad we finally came to consensus on this! phew! > It happens sometimes ;) Cheers, Lorenzo