From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 86FBC1C831A; Tue, 27 May 2025 18:30:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.9 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748370604; cv=none; b=G5aXxW2F3WoQ4H0ArDq/iC1XguIbFrwq2Qaq3OEVKZuHS578jukHqU4TPUguFFun1N2xrMuNBGRV0GENDdyXuVlyHncyV9vn014Pual9UZ+OPcCkYAPHE8jL/TFxpyJJINjuUpoDXfZbXbA4h8yCYBmQriJqXiumTIGp0R/OiE4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748370604; c=relaxed/simple; bh=RFurYCdEUO0yOEQnE9watUxCYa5ZZB5PXwH8Idy7BMU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=c9v/lSNgWSu0WSINz6cmN+nhQgEBp2C7AWhrStDf7iFeM/SDYBHJL1xcUUV1lb7tHU3Mo9Yw6ez6OOYyPpAk1s1AYvCDHt1u9xVYiz6NELOGtP+a6QVmavuuw1FiCF1tHDTbRxtCuRE395Qy5L/kjaC7v5wH/pHxye9KM9doy1A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=BrUZqGVg; arc=none smtp.client-ip=192.198.163.9 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="BrUZqGVg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1748370602; x=1779906602; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=RFurYCdEUO0yOEQnE9watUxCYa5ZZB5PXwH8Idy7BMU=; b=BrUZqGVg3wEYeYVjfskZMpr1RmTjl5WLKxrIORd4qHC/7x/629q3+pmL tWscu5zFiQfdni1gx3gvhbIqK10HTt/6C33WtOD0z/1UNThh1BZQjdv8v 3zBmWvoFrwWctBNxSzsAYTvFzPHbwtEb8oFg8jbxCFmgjvSJwP2YeV9aD 7U0eD0KSU4Xhwz8mGFvMvEH74AcMqWVoiaxPZD2+yySfmLxoVRBop6//P sGrCefwcdsCBeK3454zPcCUQM8p5TdB42U8D7pLu7UJ39XNHMVKOLglkD GETRjyFFKq9Z7G/ZP6J24l10C/JLFTrT0LWSLa3R0zHr2qPMO0dTIAKXe A==; X-CSE-ConnectionGUID: ogRdzQpvTK6OGVycUpCaYg== X-CSE-MsgGUID: cP6iS/FBRGCfa5Dbklr4Ww== X-IronPort-AV: E=McAfee;i="6700,10204,11446"; a="61037619" X-IronPort-AV: E=Sophos;i="6.15,319,1739865600"; d="scan'208";a="61037619" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 May 2025 11:30:01 -0700 X-CSE-ConnectionGUID: 3khMpL2CS5qbgv7QE88M2Q== X-CSE-MsgGUID: 2bVqcw98QmSd9Vqwf/wVcg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,319,1739865600"; d="scan'208";a="180141946" Received: from spandruv-desk1.amr.corp.intel.com (HELO [10.125.109.244]) ([10.125.109.244]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 May 2025 11:30:01 -0700 Message-ID: <1c1f0ad7-8668-406b-9e4c-59ee52f816b3@intel.com> Date: Tue, 27 May 2025 11:30:00 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 2/3] mm: add STATIC_PMD_ZERO_PAGE config option To: "Pankaj Raghav (Samsung)" Cc: Pankaj Raghav , Suren Baghdasaryan , Ryan Roberts , Vlastimil Babka , Baolin Wang , Borislav Petkov , Ingo Molnar , "H . Peter Anvin" , Zi Yan , Mike Rapoport , Dave Hansen , Michal Hocko , David Hildenbrand , Lorenzo Stoakes , Andrew Morton , Thomas Gleixner , Nico Pache , Dev Jain , "Liam R . Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, willy@infradead.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de References: <20250527050452.817674-1-p.raghav@samsung.com> <20250527050452.817674-3-p.raghav@samsung.com> <626be90e-fa54-4ae9-8cad-d3b7eb3e59f7@intel.com> <5dv5hsfvbdwyjlkxaeo2g43v6n4xe6ut7pjf6igrv7b25y2m5a@blllpcht5euu> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <5dv5hsfvbdwyjlkxaeo2g43v6n4xe6ut7pjf6igrv7b25y2m5a@blllpcht5euu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/27/25 11:00, Pankaj Raghav (Samsung) wrote: >> I get that callers have to handle failure. But isn't this pretty nasty >> for mm==NULL callers to be *guaranteed* to fail? They'll generate code >> for the success case that will never even run. >> > The idea was to still have dynamic allocation possible even if this > config was disabled. I don't really understand what you are trying to say here. > You are right that if this config is disabled, the callers with NULL mm > struct are guaranteed to fail, but we are not generating extra code > because there are still users who want dynamic allocation. I'm pretty sure you're making the compiler generate unnecessary code. Think of this: if (mm_get_huge_zero_folio(mm) foo(); else bar(); With the static zero page, foo() is always called. But bar() is dead code. The compiler doesn't know that, so it will generate both sides of the if(). If you can get the CONFIG_... option checks into the header, the compiler can figure it out and not even generate the call to bar(). > Do you think it is better to have the code with inside an #ifdef instead > of using the IS_ENABLED primitive? It has nothing to do with an #ifdef versus IS_ENABLED(). It has to do with the compiler having visibility into how mm_get_huge_zero_folio() works enough to optimize its callers.