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Wed, 13 May 2026 19:19:00 -0700 (PDT) X-Received: by 2002:a05:620a:1708:b0:910:4023:4fc5 with SMTP id af79cd13be357-910402352f4mr609022885a.13.1778725139748; Wed, 13 May 2026 19:18:59 -0700 (PDT) Received: from [192.168.2.110] ([70.53.202.134]) by smtp.gmail.com with ESMTPSA id af79cd13be357-910bcf35843sm118154085a.38.2026.05.13.19.18.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 May 2026 19:18:59 -0700 (PDT) Message-ID: <1f4bccaf-6472-4e4c-92d0-28ac05f6f838@redhat.com> Date: Wed, 13 May 2026 22:18:48 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/9] mm: introduce pgtable_has_pmd_leaves() To: "David Hildenbrand (Arm)" , 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> <07f1039c-cf9b-4b97-a044-9d5771ea54fb@kernel.org> From: Luiz Capitulino In-Reply-To: <07f1039c-cf9b-4b97-a044-9d5771ea54fb@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: LX_46Yag6xfg633IJB2Eu9GQSQlRss9MGCssycd-IIc_1778725140 X-Mimecast-Originator: redhat.com Content-Language: en-US, en-CA Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A092EA0002 X-Rspamd-Server: rspam04 X-Stat-Signature: dwqrhzty3wsksfmzkmf6ogbs31nmpo7a X-HE-Tag: 1778725142-37563 X-HE-Meta: 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 YqWXeNaY 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026-05-13 11:36, David Hildenbrand (Arm) wrote: > 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. > > Oh, one more thing: what will be the semantics regarding > CONFIG_TRANSPARENT_HUGEPAGE? > > I assume it will only return true if CONFIG_TRANSPARENT_HUGEPAGE is enabled, > correct? > > That is, for example, relevant for patch #2. > > We could later change these semantics, but for now we should be very clear about > what it means. I intended to decouple the API from CONFIG_TRANSPARENT_HUGEPAGE,so my goal was to return true as long as PMD-sized pages are supported[*]. If arch_has_pmd_leaves() is not implemented by the arch, we default to CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE, not CONFIG_TRANSPARENT_HUGEPAGE. Now, do you mean to say that the API should still be tied to CONFIG_TRANSPARENT_HUGEPAGE? If yes, why? * Sashiko found out that the current arch_has_pmd_leaves() implementation for x86 (and possibly the other archs) is guarded by CONFIG_TRANSPARENT_HUGEPAGE, so we may return true without the hardware check. But that's a bug