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X-CSE-ConnectionGUID: BcKhmJ5HQyelSxACsnUMCw== X-CSE-MsgGUID: WI83s0BiRhyBpA1FaU2KrQ== X-IronPort-AV: E=McAfee;i="6800,10657,11690"; a="71263362" X-IronPort-AV: E=Sophos;i="6.21,269,1763452800"; d="scan'208";a="71263362" 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 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 X-Rspamd-Server: rspam12 X-Stat-Signature: bmhu3b1895tzmbxd17ieshqy34hhco85 X-Rspamd-Queue-Id: BA284180008 X-Rspam-User: X-HE-Tag: 1770049216-417422 X-HE-Meta: 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 YzMZe/0D LiF5kIxrN4BLK8T91qz1o4micD1wVtw7jsBYfWMVBCbZfZ9qb64XAMWs+zI5Njna9Kj46OJbZHzSzMFnkUjbYrTHedCD3CNOGtSeJbLT9iG+l27J7nH9NZtuHodRlaAtZerQOhd8njtk7nnrT9qKw6I624wyFYJh6EVJUaqFM3RFre9R6fdTkuodVI1M12G6pjXvWm000zaIqX6l0PpuKL+tk2nNn7x3GLc8XO/0r6VWfMREqISB17Rku3IbS7uviuRlF 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 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?