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[70.30.145.63]) by smtp.gmail.com with ESMTPSA id p13-20020a05620a056d00b007208dd55183sm359687qkp.40.2023.02.02.12.04.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 12:04:47 -0800 (PST) Date: Thu, 2 Feb 2023 15:04:46 -0500 From: Peter Xu To: Yang Shi Cc: David Stevens , David Hildenbrand , "Kirill A. Shutemov" , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Hugh Dickins Subject: Re: [PATCH] mm/khugepaged: skip shmem with armed userfaultfd Message-ID: References: <20230201034137.2463113-1-stevensd@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4E00D16000A X-Rspam-User: X-Stat-Signature: zp1jtiu9xkmq5c8xjdi7q36adgtcgek3 X-HE-Tag: 1675368293-45754 X-HE-Meta: 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 9Cd4cmWS AZRqZX+C1iV/KbKQUqe+GwmRcVifqIBUW3s4iD3M3ttuXe7XH7AcOx9FaSpLze/HlZ8YqwFaqgz43N/Zly/rmEbdMtNCPPoRJmN+YipVNDFjTysPTKPv7zVZXWahEOk8CfzT53qRoeQhpabM3yvt49vpWRhs7aO5x5ufBAvuLLkZ17XoCl52uB2Wp9uKtBoCv7F3N6caplsYaIkkgqKAJ8GzUZTJxC6NoC4K3qKPiePQb7Fj/nlYoUkY9TYAbkR235Huocan4PBmkm9JCLDU9ahOXuMOfgPzN2ksmNGSJAxMCRvhlO4iVV+bXAi3o70vZbxQFDG2ZWHjU/cdiYA4LZ/0z6Bf6zcztZiybTwMsg3OoE6mI6tvau27d7NZ4XCWHsZ6X X-Bogosity: Ham, tests=bogofilter, spamicity=0.000013, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 01, 2023 at 03:57:33PM -0800, Yang Shi wrote: > > There's another problem where the current vma may not have uffd armed, > > khugepaged may think it has nothing to do with uffd and moved on with > > collapsing, but actually it's armed in another vma of either the current mm > > or just another mm's. > > Out of curiosity, could you please elaborate how another vma armed > with userfaultfd could have an impact on the vmas that are not armed? It's e.g. when >1 vmas mapped to the same shmem file on the same range, one registered with uffd missing, others not. Then others can cause page cache populated without generating message to the vma that got uffd missing mode registered, so there'll be the same issue as when khugepaged accidentally does thp collapsings. Thanks, -- Peter Xu