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Shutemov" , Minchan Kim , SeongJae Park , Pasha Tatashin Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: DCF4740012 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=NQXlRHzk; spf=pass (imf04.hostedemail.com: domain of shy828301@gmail.com designates 209.85.210.180 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: ywaq6636qt4y7gsrtn64m54ij9dihius X-HE-Tag: 1653499961-920937 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: On Wed, May 25, 2022 at 1:24 AM Michal Hocko wrote: > > On Mon 23-05-22 17:18:32, Zach O'Keefe wrote: > [...] > > Idea: MADV_COLLAPSE should respect VM_NOHUGEPAGE and "never" THP mode, > > but otherwise would attempt to collapse. > > I do agree that {process_}madvise should fail on VM_NOHUGEPAGE. The > process has explicitly noted that THP shouldn't be used on such a VMA > and seeing THP could be observed as not complying with that contract. > > I am not so sure about the global "never" policy, though. The global > policy controls _kernel_ driven THPs. As the request to collapse memory > comes from the userspace I do not think it should be limited by the > kernel policy. I also think it can be beneficial to implement userspace > based THP policies and exclude any kernel interference and that could be > achieved by global kernel "never" policy and implement the whole > functionality by process_madvise. I'd prefer to respect "never" for now since it is typically used to disable THP globally even though the mappings are madvised (MADV_HUGEPAGE). IMHO I treat MADV_COLLAPSE as weaker MADV_HUGEPAGE (take effect for non-madvised mappings but not flip VM_NOHUGEPAGE) + best-effort synchronous THP collapse. We could lift the restriction in the future if it turns out non respecting "never" is more useful. > -- > Michal Hocko > SUSE Labs