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X-CSE-ConnectionGUID: qpqNyGJTRPyhNydyRnRe2g== X-CSE-MsgGUID: FwFct6fCTfqy7FGckT1zZA== X-IronPort-AV: E=McAfee;i="6800,10657,11578"; a="87838068" X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="87838068" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 23:34:32 -0700 X-CSE-ConnectionGUID: VcSPh3W0SuyKVz7g68oZuw== X-CSE-MsgGUID: hnXs8JcbTyOib7kc4CEhjA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="204824426" Received: from allen-sbox.sh.intel.com (HELO [10.239.159.30]) ([10.239.159.30]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 23:34:27 -0700 Message-ID: <7a001cb9-fb09-487c-bfa9-e2d329b0f6a8@linux.intel.com> Date: Sat, 11 Oct 2025 14:30:54 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page tables To: David Hildenbrand , Joerg Roedel , Will Deacon , Robin Murphy , Kevin Tian , Jason Gunthorpe , Jann Horn , Vasant Hegde , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Alistair Popple , Peter Zijlstra , Uladzislau Rezki , Jean-Philippe Brucker , Andy Lutomirski , Yi Lai Cc: iommu@lists.linux.dev, security@kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen References: <20250919054007.472493-1-baolu.lu@linux.intel.com> <20250919054007.472493-7-baolu.lu@linux.intel.com> <5b494700-a3af-4feb-8c5f-1ca424ad9841@redhat.com> Content-Language: en-US From: Baolu Lu In-Reply-To: <5b494700-a3af-4feb-8c5f-1ca424ad9841@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: su57j495ugbrh5yosj9c3s84mwqgn4yx X-Rspamd-Queue-Id: 7E3AF180003 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1760164473-635714 X-HE-Meta: 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 VW4skhph 9cxqMYGywe7S7g6uqSVt6F2nt8CvzuhDEYsHhgyFPR3ilME36+c8EM7uOefOYiIqn2mwqDUmguGLSOLGh+tULqCl+cqK4TIGG8Hf3QuDCU2Eh7watWhWpXgQh4C/QP/KZ0iFyF/bONAnvN6L7lKeV0B0bFfUVCjjsAZVvIE+pYNNZbUhmw6XM1mNhkEKgWIalcOxC 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 10/10/25 23:47, David Hildenbrand wrote: > On 19.09.25 07:40, Lu Baolu wrote: >> From: Dave Hansen >> >> This introduces a conditional asynchronous mechanism, enabled by >> CONFIG_ASYNC_PGTABLE_FREE. When enabled, this mechanism defers the >> freeing >> of pages that are used as page tables for kernel address mappings. These >> pages are now queued to a work struct instead of being freed immediately. >> > > Okay, I now looked at patch #8 and I think the whole reason of this > patch is "batch-free page tables to minimize the impact of an expensive > cross-page table operation" which is a single TLB flush. > >> This deferred freeing provides a safe context for a future patch to add > > So I would claridy here instead something like > > "This deferred freeing allows for batch-freeing of page tables, > providing a safe context for performing a single expensive operation > (TLB flush) for a batch of kernel page tables instead of performing that > expensive operation for each page table." The commit message has been updated, and CONFIG_ASYNC_PGTABLE_FREE has been replaced with CONFIG_ASYNC_KERNEL_PGTABLE_FREE. Thank you for the comments. Thanks, baolu