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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 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 X-Stat-Signature: hobdjhry5jcp9awbkfjz6p9ryg1uuafp X-Rspamd-Queue-Id: A0538C001F X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778686261-156894 X-HE-Meta: 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 JD9smIbg 0s4fTgHhGw5mMazur42+9cbmsD/U1pvyBKuL5M8mZbVq6i7LFLusj0SBTMrk5AEYcF+P6dFemN12Z2owVFJnXNf4d51ep7JLuALJDUFiPM4EaVIapgaY4FvrBW0kgAxvHYZY/nRsjwBKKhmduXxkhDYzI7zpUHT1YG3irvAu5LASl3LHrEn2Fnb5W4bxYcc9OU116eOfStZ3EhY3V1ge5DEMvTTAUIVUX+xBJqTYpbNIBYi9CYYqhwxvOmGwHy4qIETs2YuVFe0az0WXgEu7lG7yVasWoDeNAWmgRPDvgWI7QHmTilaB9bSWj9JvhDG38Q5WJiVDgDoZtRhU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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