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bh=UsNEwFWdf8+xj8apQ2tpCjXCCbHBW+SvnxbyipiMG7c=; b=kWVLS6d4m+EdcwV3DiEN+Tq0iCErqJGk2iwi7xF+AVXRlYxWVxHuSBbykXREOtAi1RWMQA 8ayx646x4C82OrGgSupCiDY55xXdldBUUmGU/RAvhqvBKsgO8r29iOc8gOtKb2QMTmxoTV Boe4qN6fO+Kl8Ciz820pgNZ5sK/hKM262a/Ahb+qUNK1h4zkPb0LcGYp1n+mN0jlYg0GEk qm8hRO8nm9alfzkHePtvVRTB9ZaFJiNoE7Q7j9+N++paHbPLmus4EffeRREhL4VG6ZF/Id 8/CqVJUwrr6vpTPzNWFUIrp+TFHPjA7pNNcNlDoqSoduukWH+JIFzbNaYYY4NA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1733925844; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UsNEwFWdf8+xj8apQ2tpCjXCCbHBW+SvnxbyipiMG7c=; b=OKKVRjHggoTfjau/0sKye5pPUjMe8nsbgsOCCpYuo4jyTYQistgxgsYQz4pnoDQjFIFnH7 FAG0k5Ffj1lb+UDw== From: Sebastian Andrzej Siewior To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Arnd Bergmann , linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, Ard Biesheuvel , Clark Williams , Jason Baron , Josh Poimboeuf , Linus Walleij , Mark Rutland , Matthew Wilcox , Peter Zijlstra , Russell King , Steven Rostedt Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels Message-ID: <20241211140402.yf7gMExr@linutronix.de> References: <20241210160556.2341497-1-arnd@kernel.org> <20241210160556.2341497-3-arnd@kernel.org> <20241211134811.wM_UADhQ@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20241211134811.wM_UADhQ@linutronix.de> X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C1CA3140026 X-Stat-Signature: jninjkas7pqemms9mod1qfwtxtuadk1s X-HE-Tag: 1733925830-349649 X-HE-Meta: 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 CHh7M739 J9pb1SbtR3UisStUY2M6+I38LpnxOXxkjZhcyGCP7veLmvK4sXKBwhhTpV44TnNfCEfZkiYba/5B18LyYeVxo4KVrNYohWlggVRFH+XDtddCCiO6SgfZGupxF25T085CQ68p5ybMh1Nf/XO+SBM0h3/fJx4DW6xYUwOe+YI9mvDOCZjE/TH6LC7EmKEVdIqDA0CZwohm94g7E7yY= 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 2024-12-11 14:48:11 [+0100], To Arnd Bergmann wrote: > I guess if you have boxes with 4GiB+ and can proof that the performance > improves without HIGHPTE (since you don't have to map the page table). > The question is then how much of low mem has to be used instead and when > does it start to hurt. Some numbers have been been documented in commit 14315592009c1 ("x86, mm: Allow highmem user page tables to be disabled at boot time") and I would like cite: | We could probably handwave up an argument for a threshold at 16G of total | RAM. which means HIGHPTE would make sense with >= 16GiB of memory. Sebastian