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X-CSE-ConnectionGUID: ayu3E7LVSxiC86vO8v+43g== X-CSE-MsgGUID: 97TYavGLQJmwuShnBYdd5Q== X-IronPort-AV: E=McAfee;i="6800,10657,11690"; a="71263368" X-IronPort-AV: E=Sophos;i="6.21,269,1763452800"; d="scan'208";a="71263368" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Feb 2026 08:20:15 -0800 X-CSE-ConnectionGUID: vGtb2QeURBqmGgaBVcjwTA== X-CSE-MsgGUID: AHy1YBBZQ3e5qR8b6S8+Ww== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,269,1763452800"; d="scan'208";a="214089413" Received: from spandruv-desk1.amr.corp.intel.com (HELO [10.125.110.145]) ([10.125.110.145]) by orviesa004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Feb 2026 08:20:15 -0800 Message-ID: Date: Mon, 2 Feb 2026 08:20:13 -0800 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] mm: use targeted IPIs for TLB sync with lockless page table walkers To: Lance Yang , Peter Zijlstra Cc: akpm@linux-foundation.org, david@kernel.org, dave.hansen@linux.intel.com, ypodemsk@redhat.com, hughd@google.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shy828301@gmail.com, riel@surriel.com, jannh@google.com, jgross@suse.com, seanjc@google.com, pbonzini@redhat.com, boris.ostrovsky@oracle.com, virtualization@lists.linux.dev, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com References: <20260202074557.16544-1-lance.yang@linux.dev> <20260202074557.16544-2-lance.yang@linux.dev> <20260202094245.GD2995752@noisy.programming.kicks-ass.net> <0f44dfb7-fce3-44c1-ab25-b013ba18a59b@linux.dev> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/2/26 04:14, Lance Yang wrote: >>> Note that the tracking adds ~3% latency to GUP-fast, as measured on a >>> 64-core system. >> >> What architecture, and that is acceptable? > > x86-64. > > I ran ./gup_bench which spawns 60 threads, each doing 500k GUP-fast > operations (pinning 8 pages per call) via the gup_test ioctl. > > Results for pin pages: > - Before: avg 1.489s (10 runs) > - After:  avg 1.533s (10 runs) > > Given we avoid broadcast IPIs on large systems, I think this is a > reasonable trade-off 🙂 I thought the big databases were really sensitive to GUP-fast latency. They like big systems, too. Won't they howl when this finally hits their testing? Also, two of the "write" side here are: * collapse_huge_page() (khugepaged) * tlb_remove_table() (in an "-ENOMEM" path) Those are quite slow paths, right? Shouldn't the design here favor keeping gup-fast as fast as possible as opposed to impacting those?