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X-CSE-ConnectionGUID: +yofWxBHQRyJDGPGbwYyPQ== X-CSE-MsgGUID: wzau2yDiTcOjeJAY8ApGfg== X-IronPort-AV: E=McAfee;i="6800,10657,11711"; a="72865529" X-IronPort-AV: E=Sophos;i="6.21,308,1763452800"; d="scan'208";a="72865529" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa111.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Feb 2026 07:04:11 -0800 X-CSE-ConnectionGUID: dRHuQAc+RVCWEUEFFqIq3w== X-CSE-MsgGUID: XmJNjA2GSgeSBLo9G/u1dw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,308,1763452800"; d="scan'208";a="213159563" Received: from gabaabhi-mobl2.amr.corp.intel.com (HELO [10.125.110.247]) ([10.125.110.247]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Feb 2026 07:04:10 -0800 Message-ID: <95c65dab-8a48-4449-aa96-3928f035b07b@intel.com> Date: Tue, 24 Feb 2026 07:04:10 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] mm/mmu_gather: replace IPI with synchronize_rcu() when batch allocation fails To: Peter Zijlstra , Lance Yang Cc: akpm@linux-foundation.org, david@kernel.org, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260224030700.35857-1-lance.yang@linux.dev> <20260224114152.GX1395266@noisy.programming.kicks-ass.net> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3F7A74001C X-Stat-Signature: jzinn71eu69918dfwudm96fsjgapx1xg X-HE-Tag: 1771945452-166545 X-HE-Meta: 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 NaWovrR0 6H+m8mMw941QhJ5qVi9wqghkLe9iAdvCi/52vH1J6uaQYQj3qYUm6Fy8vrg9HziZo/5cEyMotfGAaoj4zacCYxxIGr8MsLejyYO8t0QKpNvFwxzBlOSMtAc/FTGLMRFcVnEhOTEF4l15cPQsYgurwFT4iEsCExSGMwyaXGT72BNSnw6EZybgFrJzOKcSgK/jRyoohPgR1B5RUOz5trmEBXT/cXMRORkBtIjTMlKUAQmG96Pmy/proU3dSqA== 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 2/24/26 03:41, Peter Zijlstra wrote: >> +void tlb_remove_table_sync_rcu(void) >> +{ >> + might_sleep(); >> + synchronize_rcu(); > synchronize_rcu() should end up in a might_sleep() at some point if it > blocks (which it typically will). FWIW, I do prefer the explicit might_sleep() rather than leaving it to just the documentation. It just makes it easier to find bugs. I'm sure there's some crazy RCU variant that doesn't often sleep in synchronize_rcu(). ;) If it's worth adding a line of comment, it's worth adding a line of code to actually keep folks honest. This is also going to be a pretty darn slow path so it shouldn't bloat anything too much.