From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CE98E481238 for ; Wed, 13 May 2026 15:31:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778686260; cv=none; b=N5t+zCgSSQx9CJNBhKE5ef/0H9X3fJt+L1y8YRzAvBv6xf9SaZQRcfQjZXevD3nScnkFehqIQbGsaYkEiEtGgMM5YKvI3EIACBulH9LkqGXlihaxcmVL+hrDrAiVRv5X/gDEUQn/MXl0+xoZrKNsrfprYOiEMSxfUSEnvQGX7rI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778686260; c=relaxed/simple; bh=HxOcaNkSWUrdTUDltrD5t+kOiINvTITwK0zOY8qgjio=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qvFd4WoG4yF5WZDF+K5an/7/IgY0pVek0R99kf1IKEUxnaWvAd0R7laanrbgrcFPMH9Y2UjMmIJD2PpClYco4Sk1rrbObu2MOcjE6qR4eu+A2Qh/9fAin7S+lxbOv3WZctx2dEt02tyOE4pseqPQMwFmcJNfK55NzwgPoNHZ9xI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vQ69U3Jg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vQ69U3Jg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCB27C2BCC6; Wed, 13 May 2026 15:30:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778686260; bh=HxOcaNkSWUrdTUDltrD5t+kOiINvTITwK0zOY8qgjio=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=vQ69U3JgJfPfLgdPT89HklCWlbGxdnacToxrAy+GebEnGkVo5+GinCzNpjtLlsxt9 zrqh9kh3urTQ1/IrAvUc1EJgA+ZKuV3lnzGRlouyg6U5WMafMRqwyFO4Q6NcBYHbqq p4RhwSZM8+yJAEDgrJ23ddmmipAP2tOlgy8gCqdaxfz4cVDSgPdZHmdhONYYQs5qWk v53ozJXLnHNPUSe5T0fK+JFAsLjTkohmiyIVvj9QXloQH6/aAiHkfywJmkSUGq/wWq Y/9X27rIcD/k0e1pDbWHJ1aHbzpvQkGCUcD4uBYb1KLD7+Ouqo14Mn9vvqdb8182S2 3Cocbx/HILB4g== Message-ID: <8683a04e-54e9-4e8e-8931-69e31d15b99b@kernel.org> Date: Wed, 13 May 2026 17:30:51 +0200 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 v4 2/9] mm: introduce pgtable_has_pmd_leaves() To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev Cc: corbet@lwn.net, tsbogend@alpha.franken.de, maddy@linux.ibm.com, mpe@ellerman.id.au, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, x86@kernel.org, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com References: <2a0bae00cdd2b6ef6b962610b523ebfc97806ba7.1777663129.git.luizcap@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/1/26 21:18, Luiz Capitulino wrote: > Currently, we have two helpers that check for PMD-sized pages but have > different names and slightly different semantics: > > - has_transparent_hugepage(): the name suggests it checks if THP is > enabled, but when CONFIG_TRANSPARENT_HUGEPAGE=y and the architecture > implements this helper, it actually checks if the CPU supports > PMD-sized pages > > - thp_disabled_by_hw(): the name suggests it checks if THP is disabled > by the hardware, but it just returns a cached value acquired with > has_transparent_hugepage(). This helper is used in fast paths > > This commit introduces a new helper called pgtable_has_pmd_leaves() > which is intended to replace both has_transparent_hugepage() and > thp_disabled_by_hw(). pgtable_has_pmd_leaves() has very clear semantics: > it returns true if the CPU supports PMD-sized pages and false otherwise. > It always returns a cached value, so it can be used in fast paths. > > The new helper requires an initialization step which is performed by > init_arch_has_pmd_leaves(). We call init_arch_has_pmd_leaves() early > during boot in start_kernel() right after parse_early_param() but before > parse_args(). This allows early_param() handlers to change CPU flags if > needed (eg. parse_memopt() in x86-32) while also allowing users to use > the API from __setup() handlers. > > The next commits will convert users of both has_transparent_hugepage() > and thp_disabled_by_hw() to pgtable_has_pmd_leaves(). > > Signed-off-by: Luiz Capitulino > --- > include/linux/pgtable.h | 15 +++++++++++++++ > init/main.c | 1 + > mm/memory.c | 9 +++++++++ > 3 files changed, 25 insertions(+) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index cdd68ed3ae1a..b365be3516bf 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -2243,6 +2243,21 @@ static inline const char *pgtable_level_to_str(enum pgtable_level level) > } > } > > +#ifdef CONFIG_MMU > +DECLARE_STATIC_KEY_TRUE(__arch_has_pmd_leaves_key); > +static inline bool pgtable_has_pmd_leaves(void) > +{ > + return static_branch_likely(&__arch_has_pmd_leaves_key); > +} > +void __init init_arch_has_pmd_leaves(void); > +#else > +static inline bool pgtable_has_pmd_leaves(void) > +{ > + return false; > +} > +static inline void __init init_arch_has_pmd_leaves(void) { } > +#endif > + > #endif /* !__ASSEMBLY__ */ > > #if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT) > diff --git a/init/main.c b/init/main.c > index 96f93bb06c49..eea7c5bdddf7 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -1053,6 +1053,7 @@ void start_kernel(void) > print_kernel_cmdline(saved_command_line); > /* parameters may set static keys */ > parse_early_param(); > + init_arch_has_pmd_leaves(); Can't we do this a bit later from some mm code? This feels like something that can just go somewhere into mm_core_init()? There, we should probably call this something like XXX_init(), and prepare it from detecting support for PUD leaves as well. Maybe just pgtable_init() ? -- Cheers, David