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[95.203.13.87]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-2ffdfbef4aasm18466261fa.34.2024.12.04.00.51.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Dec 2024 00:51:10 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 4 Dec 2024 09:51:07 +0100 To: Matthew Wilcox Cc: Uladzislau Rezki , Kefeng Wang , zuoze , gustavoars@kernel.org, akpm@linux-foundation.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, keescook@chromium.org Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check. Message-ID: References: <92768fc4-4fe0-f74a-d61c-dde0eb64e2c0@huawei.com> <76995749-1c2e-4f78-9aac-a4bff4b8097f@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4571F40005 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: hqxtrtgtox567rqiheoese8qh677y6pb X-HE-Tag: 1733302255-563875 X-HE-Meta: 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 APpN6Tf+ 5XEtYsenFdzpGz+SssLRWKQ9fvmlf0OS7lL8OW6XSggDC+SD1LxYqgTvEWnF/InXgknjwni3cFy9MlplGTBMRTPYteGOaFoozrCobC5oAZFBBl25N4q/s0kRZ4FPyPeEdUCaelV/WFG59ojTACqU1S0lb/brf1F9kuYORflLo5XRUEAXlbSknHDVDTLkF0tAOn1b7QELkXeqacP75m0FqBhphYGhw5niYO+lL01hsYy7cA0cPPKwsCCo4cvS6iMBC3mt86P0oM4LPCZJxek4q5TQp8DJvP0EZR5+oD3CGI+bE7oGl0ouV03luM4yNqwYF6eNn96hM11NpuW40Kxg93VQ//wHVRr9eMfISTcq5OpZWVhNaV5y7rRZJlXbqa8VCiXSUdsyaKS1blzM= 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: List-Subscribe: List-Unsubscribe: > On Tue, Dec 03, 2024 at 08:02:26PM +0100, Uladzislau Rezki wrote: > > I think there are a few other things we can try here. > > First, if the copy is small (and I still don't have an answer to that > ...), we can skip the vmalloc lookup if the copy doesn't cross a page > boundary. > I noticed that, a path which is in question, does not supply a starting address of mapping area, instead it passes something within. > > Second, we could try storing this in a maple tree rather than an rbtree. > That gives us RCU protected lookups rather than under a spinlock. > I think, when i have more free cycles, i will check it from performance point of view. Because i do not know how much a maple tree is efficient when it comes to lookups, insert and removing. As an RCU safe data structure, yes, a searching is improved in a way there is no need in taking spinlock. As a noted earlier i do not know if a maple tree allows to find a data when instead of key, it is associated with, we pass something that is withing a searchable area: [va_start:va_end]. -- Uladzislau Rezki