From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.16]) (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 95EA92571D4; Tue, 5 Aug 2025 16:42:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754412139; cv=none; b=jnRi+fnhYhe+q58KEvYwm6ert6kA7bsmqBzoMgjNGwzEtxf6CR8Pfmn6TnhtgnKwm5s8HHOLvF8O7jgzyfzHi1Jk9LSG1GU5Ef8EOJfTYyfhe3TvByKx9nEKheKgr9+Mz0wQV/nIXAgwr4qfqAdyQRZ3ksnj2zHLCJ5d6wTY+3E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754412139; c=relaxed/simple; bh=NI0Pa52pJjxiroyoTscQkPI/Lrl+7gR5IHOHQEg0uqA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hu1K22GbmJ2B17ZZp5La0k4QXm75gFppNXYBdy1nii0UVu4J7oEbJIxWRB7c+q++dcAgpQxxyM0NC2kUmAJpcJ1FR91eoq75ytDDGyiAxEObco6eVR58NR6F2e4poUB5SCf3EPgI7qJ99KOjH/QUc9TYroFSa5Whph4frsQGnAo= 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=I4OUu/L+; arc=none smtp.client-ip=192.198.163.16 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="I4OUu/L+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1754412137; x=1785948137; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=NI0Pa52pJjxiroyoTscQkPI/Lrl+7gR5IHOHQEg0uqA=; b=I4OUu/L+MrGsc2HBGo2oVyoKIKNtmVMylL25yhLhUm7cJ2R18EWz0FK3 TsT6LlAaSyCSOe9IQTqu0vB7IR27vHml6QBrHkGh1OkzU6ILqIJkMv73Q p/6bzdvjXDsruYm34wyi6zuhqhJXtEhKp2B7j0LnQGHX2j0R1iwhJCxgS jmbDsQ5CIwqRC5hn/gQZ0CLJLnx8qb7+vznVPNsh6eNMN5gox/Mu4yTlg bf184xUmOpHVktpCU+olyR1OmkY6tseKmqTUvP+2pWFuYKimmtkVEY4U+ 1OU3a0J+I7CK84kQ+X2ST5OPkCmy1mY1jsxLWMCePyzePMRT4dYzHheMR A==; X-CSE-ConnectionGUID: m8G2J9m6RMmMs0dGOLIUnQ== X-CSE-MsgGUID: 6zxoOmOtRqWHd+vDV/1e3Q== X-IronPort-AV: E=McAfee;i="6800,10657,11513"; a="44309751" X-IronPort-AV: E=Sophos;i="6.17,268,1747724400"; d="scan'208";a="44309751" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by fmvoesa110.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2025 09:42:16 -0700 X-CSE-ConnectionGUID: 2zo8793CR+SS/fNQvNF4lA== X-CSE-MsgGUID: Waiv5Ff0Q8u+GwM8Ts8yjw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.17,268,1747724400"; d="scan'208";a="164905002" Received: from inaky-mobl1.amr.corp.intel.com (HELO [10.125.110.106]) ([10.125.110.106]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2025 09:42:15 -0700 Message-ID: Date: Tue, 5 Aug 2025 09:42:14 -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: [PATCH 4/5] mm: add largest_zero_folio() routine To: "Pankaj Raghav (Samsung)" , Suren Baghdasaryan , Ryan Roberts , Baolin Wang , Borislav Petkov , Ingo Molnar , "H . Peter Anvin" , Vlastimil Babka , 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, willy@infradead.org, x86@kernel.org, linux-block@vger.kernel.org, Ritesh Harjani , linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de, Pankaj Raghav References: <20250804121356.572917-1-kernel@pankajraghav.com> <20250804121356.572917-5-kernel@pankajraghav.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: <20250804121356.572917-5-kernel@pankajraghav.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/4/25 05:13, Pankaj Raghav (Samsung) wrote: > From: Pankaj Raghav > > Add largest_zero_folio() routine so that huge_zero_folio can be > used directly when CONFIG_STATIC_HUGE_ZERO_FOLIO is enabled. This will > return ZERO_PAGE folio if CONFIG_STATIC_HUGE_ZERO_FOLIO is disabled or > if we failed to allocate a huge_zero_folio. This changelog is telling a lot of the "what" but none of the "why". The existing huge zero folio API is for users that have an mm. This is *only* for folks that want a huge zero folio but don't have an mm. That's _why_ this function is needed. It's in this series because there was no way to get a huge zero folio before the permanent one was introduced in this series. Can we please get some of that into the function comment and changelog? It's critical. > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 78ebceb61d0e..c44a6736704b 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -716,4 +716,21 @@ static inline int split_folio_to_order(struct folio *folio, int new_order) > return split_folio_to_list_to_order(folio, NULL, new_order); > } > > +/* > + * largest_zero_folio - Get the largest zero size folio available > + * > + * This function will return huge_zero_folio if CONFIG_STATIC_HUGE_ZERO_FOLIO > + * is enabled. Otherwise, a ZERO_PAGE folio is returned. > + * > + * Deduce the size of the folio with folio_size instead of assuming the > + * folio size. > + */ This comment needs to get fleshed out. It at _least_ needs to say something along the lines of: Use this when a huge zero folio is needed but there is no mm lifetime to tie it to. Basically, use this when you can't use mm_get_huge_zero_folio(). > +static inline struct folio *largest_zero_folio(void) > +{ > + struct folio *folio = get_static_huge_zero_folio(); > + > + if (folio) > + return folio; There needs to be a newline in here. > + return page_folio(ZERO_PAGE(0)); > +} > #endif /* _LINUX_HUGE_MM_H */ The code is fine, but the changelog and comments need quite a bit of work.