From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (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 8C245279910; Tue, 27 May 2025 16:37:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748363877; cv=none; b=DWiAB7ceuCHJF8AZI7NguH/48Pb/g0KwDg5juDS96WTbj1gbo10RdUhP+ildMQhwvg1aJD2+xwA4WmuLeEosjysnSpGKlddFbV1lwP7P+EYeHahr5Bo4rZ+b0leZI+YJMS0J9woTyZKJn/TDBHT2B4qIXxdNT27Q4vb4Imlsre0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748363877; c=relaxed/simple; bh=cbKKCkqWwj5R3NhfMsFzcH80Kv1e6XNU0rpPm2F+hog=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=sVLG7LDGNgeI0zNrmYgRrH51jZiVgcX4774uX7MwUolKgSxUJB0aBDaWmgQX/0Wwk27hrOo61kK/1rR36vk76v3VEOUBk5PC9vTdijubWQJhh/InyxtOYbrVfa+Ekd0ZB14QArmBJu1P3pfdab7mRPYNMaPVa6vDEzbZiK1Gb9Y= 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=MmZYfj3A; arc=none smtp.client-ip=192.198.163.10 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="MmZYfj3A" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1748363876; x=1779899876; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=cbKKCkqWwj5R3NhfMsFzcH80Kv1e6XNU0rpPm2F+hog=; b=MmZYfj3AmSqb5GCgy1+WeVKwkR+1mkPC9CoKMCERwOQpyt4IGc1K2/UN 9nN/tkBLfCP6XE6xRUxDnQD5SgkDsIjC227Go/tAqneZj94mrmoPWd0IK Y/PqVNUH0FLtuQIglv96vsbXHZb3VNL/bOnfCdNC30GVsYfbdp5w8YFNz GzYMwGzoUaJajJrmUtt211r/Z4MRrPbM890BF9n5FbkVqI7E5/Ar5aO7b X4SsN7I8M9iNwFvCiLhTnz0k5fbbjs8ylEuFprSCW3TG3mQSJbKWiteUL c36V6ao0NM9jvzVd50hA+dCqtXBW6ULjOQmBcsvnWCk9tdR4W2ZUkzeE/ A==; X-CSE-ConnectionGUID: n82G4WRoQM6FAic1j1Xs4w== X-CSE-MsgGUID: C36ke6zxQ+ypUYW86XDHVg== X-IronPort-AV: E=McAfee;i="6700,10204,11446"; a="61714972" X-IronPort-AV: E=Sophos;i="6.15,318,1739865600"; d="scan'208";a="61714972" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 May 2025 09:37:54 -0700 X-CSE-ConnectionGUID: OUcSBdMeQOWnHX/hgemOrg== X-CSE-MsgGUID: 5kud2WDqSQK4loLjiAmDkw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,318,1739865600"; d="scan'208";a="180092453" 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 09:37:50 -0700 Message-ID: <626be90e-fa54-4ae9-8cad-d3b7eb3e59f7@intel.com> Date: Tue, 27 May 2025 09:37:50 -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 , 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 Cc: 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, kernel@pankajraghav.com, hch@lst.de References: <20250527050452.817674-1-p.raghav@samsung.com> <20250527050452.817674-3-p.raghav@samsung.com> 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: <20250527050452.817674-3-p.raghav@samsung.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 055204dc211d..96f99b4f96ea 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -152,6 +152,7 @@ config X86 > select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP if X86_64 > select ARCH_WANT_HUGETLB_VMEMMAP_PREINIT if X86_64 > select ARCH_WANTS_THP_SWAP if X86_64 > + select ARCH_WANTS_STATIC_PMD_ZERO_PAGE if X86_64 I don't think this should be the default. There are lots of little x86_64 VMs sitting around and 2MB might be significant to them. > +config ARCH_WANTS_STATIC_PMD_ZERO_PAGE > + bool > + > +config STATIC_PMD_ZERO_PAGE > + def_bool y > + depends on ARCH_WANTS_STATIC_PMD_ZERO_PAGE > + help > + Typically huge_zero_folio, which is a PMD page of zeroes, is allocated > + on demand and deallocated when not in use. This option will always > + allocate huge_zero_folio for zeroing and it is never deallocated. > + Not suitable for memory constrained systems. "Static" seems like a weird term to use for this. I was really expecting to see a 2MB object that gets allocated in .bss or something rather than a dynamically allocated page that's just never freed. > menuconfig TRANSPARENT_HUGEPAGE > bool "Transparent Hugepage Support" > depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT > diff --git a/mm/memory.c b/mm/memory.c > index 11edc4d66e74..ab8c16d04307 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -203,9 +203,17 @@ static void put_huge_zero_page(void) > BUG_ON(atomic_dec_and_test(&huge_zero_refcount)); > } > > +/* > + * If STATIC_PMD_ZERO_PAGE is enabled, @mm can be NULL, i.e, the huge_zero_folio > + * is not associated with any mm_struct. > +*/ 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.