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[95.203.13.87]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-300110d4800sm3962711fa.83.2024.12.04.01.27.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Dec 2024 01:27:11 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 4 Dec 2024 10:27:09 +0100 To: zuoze Cc: Uladzislau Rezki , Matthew Wilcox , Kefeng Wang , 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: <76995749-1c2e-4f78-9aac-a4bff4b8097f@huawei.com> <2dae287b-c645-3773-4f99-fd44902ae589@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2dae287b-c645-3773-4f99-fd44902ae589@huawei.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A1553180005 X-Stat-Signature: 7n6dxse4n7pcyocpquxj6wak9s571uyr X-Rspam-User: X-HE-Tag: 1733304419-740740 X-HE-Meta: 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 UfuS6azp Y620ezQGyuCUpghLXLI+va+NSKntUKbRf1AsnsEL563hCLXBiSZS4siWnDRIA/vMSF4PE/lMt+AgEHgdBoYG9hmUHdhRPsrhWBk1hN7sNxSZfi8WFcNBrJlQcYkXWl/Mm6+aKKCoEPsil9pfOP0KBnF/zGN8UHcT1IffW4J9HXtAGdNB7VZCxXoIq1im63g7oMAzpT5ay5ZmNuorrZtM9CDX3rBIomMcFSYPHLEF3KfUhu7KIOP9n3dSP8BN82Dprylh043lSc/mAkaFIv8cM8uqPI5MrUc+1tL8urwlUm+e2ynuJ13WN2jCd7/tcsdX8sq11xnVhXQ55Svew25EaKN/Q1s7/b4SlWATmGMbyyKmOTheJFKLuniRkFDqpdSL1/nh+2cUjMus276dC1iC29mXpkbN91xONGkxc 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 Wed, Dec 04, 2024 at 05:21:12PM +0800, zuoze wrote: > > > 在 2024/12/4 15:55, Uladzislau Rezki 写道: > > On Tue, Dec 03, 2024 at 07:56:34PM +0000, Matthew Wilcox wrote: > > > 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. > > > > > > 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. > > > > > > It might even be worth going to a rwlock first, in case the problem is > > > that there's severe lock contention. > > > > > > But I've asked for data on spinlock contention and not received an > > > answer on that either, so I don't know what to suggest. > > > > > I think, it is not about contention. It is about the extra "attached > > load" when a data is heavily copied force and back. On each copy path > > you need to do a scan. Maple tree is not that something can help here :) > > > > Indeed, no contention data. Zuoze, please share this if you can. > > We have enabled perf lock contention and are currently debugging the > environment. We will share the results as soon as we have them. > Sounds good and thank you for helping to improve this :) -- Uladzislau Rezki