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[91.12.101.41]) by smtp.gmail.com with ESMTPSA id o26sm4707828wmc.17.2021.10.06.02.27.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Oct 2021 02:27:48 -0700 (PDT) Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting To: Michal Hocko , John Hubbard Cc: Suren Baghdasaryan , Pavel Machek , Andrew Morton , Colin Cross , Sumit Semwal , Dave Hansen , Kees Cook , Matthew Wilcox , "Kirill A . Shutemov" , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Al Viro , Randy Dunlap , Kalesh Singh , Peter Xu , rppt@kernel.org, Peter Zijlstra , Catalin Marinas , vincenzo.frascino@arm.com, =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , Axel Rasmussen , Andrea Arcangeli , Jann Horn , apopple@nvidia.com, Yu Zhao , Will Deacon , fenghua.yu@intel.com, thunder.leizhen@huawei.com, Hugh Dickins , feng.tang@intel.com, Jason Gunthorpe , Roman Gushchin , Thomas Gleixner , krisman@collabora.com, chris.hyser@oracle.com, Peter Collingbourne , "Eric W. Biederman" , Jens Axboe , legion@kernel.org, Rolf Eike Beer , Cyrill Gorcunov , Muchun Song , Viresh Kumar , Thomas Cedeno , sashal@kernel.org, cxfcosmos@gmail.com, Rasmus Villemoes , LKML , linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm , kernel-team References: <20211001205657.815551-1-surenb@google.com> <20211001205657.815551-3-surenb@google.com> <20211005184211.GA19804@duo.ucw.cz> <20211005200411.GB19804@duo.ucw.cz> From: David Hildenbrand Organization: Red Hat Message-ID: <6b15c682-72eb-724d-bc43-36ae6b79b91a@redhat.com> Date: Wed, 6 Oct 2021 11:27:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.10.21 10:27, Michal Hocko wrote: > On Tue 05-10-21 23:57:36, John Hubbard wrote: > [...] >> 1) Yes, just leave the strings in the kernel, that's simple and >> it works, and the alternatives don't really help your case nearly >> enough. > > I do not have a strong opinion. Strings are easier to use but they > are more involved and the necessity of kref approach just underlines > that. There are going to be new allocations and that always can lead > to surprising side effects. These are small (80B at maximum) so the > overall footpring shouldn't all that large by default but it can grow > quite large with a very high max_map_count. There are workloads which > really require the default to be set high (e.g. heavy mremap users). So > if anything all those should be __GFP_ACCOUNT and memcg accounted. > > I do agree that numbers are just much more simpler from accounting, > performance and implementation POV. +1 I can understand that having a string can be quite beneficial e.g., when dumping mmaps. If only user space knows the id <-> string mapping, that can be quite tricky. However, I also do wonder if there would be a way to standardize/reserve ids, such that a given id always corresponds to a specific user. If we use an uint64_t for an id, there would be plenty room to reserve ids ... I'd really prefer if we can avoid using strings and instead using ids. -- Thanks, David / dhildenb