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[95.203.13.87]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-53e1b975d7asm287863e87.82.2024.12.03.23.56.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Dec 2024 23:56:01 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 4 Dec 2024 08:55:58 +0100 To: Matthew Wilcox , Kefeng Wang , zuoze 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-Stat-Signature: fgfca5wyn41m8rfqco7g87fb6pr149d6 X-Rspam-User: X-Rspamd-Queue-Id: 61E4318000E X-Rspamd-Server: rspam08 X-HE-Tag: 1733298954-833706 X-HE-Meta: U2FsdGVkX19ru+DHvwz/KidU26Beb0zceXhEgnf664KjPR6mF5Af2/pOJyIT3odCtj3ISxRZvCK00vEVlf6UplpOEyTY3lVTyTSpPT1tJ2Pwq3h63h4x03IRjBkuu/LHCnWb70BOHydbqFzBcL4Y5ntdDknlbKAASEIkP5ZTustmT5e62KuO9mossDKFA8S/dTX50xw32h1xNQ/RqmdSL1TP/BzUZDOuTRCUHnLZYBEfraRCdBJNx6yw1MvXg/R1C5XXEoewtWwClufg6mFX4VioSiX6KiYCgspGWBWxbr3sfvaC3j/owu/0o4kc5O48MUTfjyV0sIdIMW6Pl7nBYlBjNAkDteOsKdNoVUFPR/xZXWElIIpKG5baZg0LGits1NmIWgdfi5GBfkWhYOUEi3MOIVjXkrklLX6T5diuRq64dAGgkIfU1OYonic6CCO9gwQlbrlO9vqT2RRS9vpB3eqBibhMd0kcf6lAcHZPmojRg6pcXatrCDyuP5UR9mPPw+SSHNk+kTcpJVjpN3QWAXXVbBpWSi6nYVp3pjUCr0LbyA7qj0ufVFYvYwYQ5d2fkBAgPoY6Qs+xaSzYNjQBWH8/VWJOxPIOjJj2MjKmV+kJfZXxIOYsBwlJTBfyS5j7Tx9IDqmpe8B4V04SBWGFLE7oWpL5JBUXFLdWBkghicPKhFlo+DBsRTQxgspkGDL6i57iNI0q1x9ta0hQCwRi2yZLpak8ZMvR66YVhE9c787RUOvL+xQH7JDy+vYVU5u8EAppGyvctRSPJTbdD8U+kRSk6mNKKi9zzN03lavjvvFeCy4oYYHneHdj0DQa5OA6FJpcazfhifEvYEBTKUDI8DEMLoRAQeMRNezKwrw/HYCZsCnrl2XOKOpXwFZykzRQp30CZhncPUXwP1uzRUbKIa2ULsh5CiFynizNiE6v9PO/t+J9Pl2ZbIvrBLoF7H7ZxMCOGhk9cibunYooPzw 1Zz3CnH1 dzWjI8NUkbqLExIOfLBgDE2KOpopT2st96s8zz3srpkzqLwWX/pOQs5djL8z6oe8kz9/1puKzLAfTPTP2k/0SRYL7VZpfyp0I3KrXFo/YFX680fb6bZAHruprWPVdORLPWkofbjf2E12PPWZ4mLcDW7c1aTHtqoAikRwAr7NY2gPoS6aqtGdoYLXiKvOk8CjP1mZWHU+uQfNdIskB5AsW8zojrrWagySDwA5XlUoOfCTGgL7a8AD7chl7ZCwj0h7ku1bWh0th3I0JO1LTf3JmJFKrs8WLgDMUmEl8YgSHrtBbbSU2PwxtvTh3o75GkInmqU7ZRQm15qEifqTfd3jXY0TnwDQrvy1PTH0yG5yf6Tlei13AaRFTbChO1jpWUvBrVU+HsTqsUCR9bH8= 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 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. -- Uladzislau Rezki