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[209.85.208.48]) by smtp.gmail.com with ESMTPSA id w5sm4279304edc.62.2021.12.21.10.59.08 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Dec 2021 10:59:09 -0800 (PST) Received: by mail-ed1-f48.google.com with SMTP id j21so51438555edt.9 for ; Tue, 21 Dec 2021 10:59:08 -0800 (PST) X-Received: by 2002:adf:8b0e:: with SMTP id n14mr3650177wra.281.1640113138726; Tue, 21 Dec 2021 10:58:58 -0800 (PST) MIME-Version: 1.0 References: <4D97206A-3B32-4818-9980-8F24BC57E289@vmware.com> <5A7D771C-FF95-465E-95F6-CD249FE28381@vmware.com> <20211221010312.GC1432915@nvidia.com> <900b7d4a-a5dc-5c7b-a374-c4a8cc149232@redhat.com> <20211221180705.GA32603@quack2.suse.cz> In-Reply-To: From: Linus Torvalds Date: Tue, 21 Dec 2021 10:58:42 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) To: David Hildenbrand Cc: Jan Kara , Jason Gunthorpe , Nadav Amit , Linux Kernel Mailing List , Andrew Morton , Hugh Dickins , David Rientjes , Shakeel Butt , John Hubbard , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Linux-MM , "open list:KERNEL SELFTEST FRAMEWORK" , "open list:DOCUMENTATION" Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 17899A001E X-Stat-Signature: du5hweahn4848omkdiu98sx7hu8pg4og Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=L0bWadFf; dmarc=none; spf=pass (imf25.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.208.52 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org X-HE-Tag: 1640113141-204007 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 Tue, Dec 21, 2021 at 10:51 AM David Hildenbrand wrote: > > For that purpose the pincount would already kind-off work. Not precise, > but at least something ("this page cannot possibly have been pinned"). That part actually exists already, ie put_page_refs() has this: #ifdef CONFIG_DEBUG_VM if (VM_WARN_ON_ONCE_PAGE(page_ref_count(page) < refs, page)) return; #endif And yeah, it shouldn't have that '#ifdef CONFIG_DEBUG_VM' there, but I think it's because the non-CONFIG_DEBUG_VM #define for VM_WARN_ON_ONCE_PAGE() is broken, and doesn't return 0. Linus