From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CF982E9904A for ; Fri, 10 Apr 2026 08:19:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 037676B0005; Fri, 10 Apr 2026 04:19:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F23A76B0089; Fri, 10 Apr 2026 04:19:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E394F6B008A; Fri, 10 Apr 2026 04:19:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id D11696B0005 for ; Fri, 10 Apr 2026 04:19:54 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 734571A0445 for ; Fri, 10 Apr 2026 08:19:54 +0000 (UTC) X-FDA: 84641947908.05.7026FC3 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) by imf05.hostedemail.com (Postfix) with ESMTP id 6748710000A for ; Fri, 10 Apr 2026 08:19:52 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=akl9dBtH; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf05.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.179 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1775809192; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=zoo8eGSkihm4pzVA3O7YxgtC1cJl7QU3sLX++hivSVg=; b=Nr5a8/HyxT5Bapd39vGF0FiL7o9nYkTRiWBjC329vU3+l6G6nPAZn3dPZjX9W+B99e60XJ DwOrB+cossdfdgPfUPh7Aa2IEcxOL5pzcfW2qYWVPoyojXokoxq/Sd6Ul6KNsblSMSAO54 Wa+Z32moZWDNNiI/DurlDkVvcLtgBZs= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1775809192; a=rsa-sha256; cv=none; b=HQWeuiCfj40843yVkAHs9XcVm3wqVaYAjVoj7mL2uXWsijRZU25tM1DYSeQ4dJugo9/UeY euT66h4MeU5G8dJNNpCY3wevGHaOCt1dC9OVqpWAsxN3NCC/dijT5s83fYJtZmyD2JgLM4 yMfOkLwSobSDcgql6GWIh1KdzVYiN/s= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=akl9dBtH; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf05.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.179 as permitted sender) smtp.mailfrom=lance.yang@linux.dev X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775809190; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zoo8eGSkihm4pzVA3O7YxgtC1cJl7QU3sLX++hivSVg=; b=akl9dBtHidnFCQuw9V6gubcDZsWwzA37+wRfKcpHSp5J4giorE+9zz+ooqFWH2mlUxi2W9 Qx+36gQebk6ImLIT4CXJKspYN9poyuLbh563Bd1vGEgEjdrNH31Rcmj6YDa9qa/NvqoQ1o Xanm0raswE1rD7u11I5yNr6+OJyysc4= From: Lance Yang To: luizcap@redhat.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, akpm@linux-foundation.org, ljs@kernel.org, ziy@nvidia.com, Liam.Howlett@oracle.com, npache@redhat.com, dev.jain@arm.com, baohua@kernel.org, Lance Yang Subject: Re: [PATCH v3 02/10] mm: introduce pgtable_has_pmd_leaves() Date: Fri, 10 Apr 2026 16:19:38 +0800 Message-Id: <20260410081938.51302-1-lance.yang@linux.dev> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 6748710000A X-Stat-Signature: f6sm51q4ezd3em7z31k7ka6b7pjxbxio X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775809192-826412 X-HE-Meta: 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 gUuoBSn1 VvGGaTfFSp7FaSECkPdt+7biIm6NIukuMMV+8U8CzNUyJz5nVdG7Y5bgWoLIjgzeiX65OD7d5RbNdBaSbKWMdtK/giekDSxgL2tOsiEnzcBojQcQdiCWs4iA07On47UgHSmLhwLwP/U/IGLIUV7kG9z05Hu1ym+JQnbkL2mJYTSDYHL+NkLt0PevVWHE5KnI8wG5XqkGGjCiV85UeBDtSCJ6AQeUNqWICGJL41ARxeMXMl866Yn7cXOFujhnRToQmNfgjDCA+BfALVsVYgAdwVyXSAw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 08, 2026 at 04:22:57PM -0400, 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 | 8 ++++++++ > 3 files changed, 24 insertions(+) > >diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >index a50df42a893f..c4c5282f795c 100644 >--- a/include/linux/pgtable.h >+++ b/include/linux/pgtable.h >@@ -2192,6 +2192,21 @@ static inline const char *pgtable_level_to_str(enum pgtable_level level) > } > } > >+#ifdef CONFIG_MMU >+extern bool __arch_has_pmd_leaves; >+static inline bool pgtable_has_pmd_leaves(void) >+{ >+ return __arch_has_pmd_leaves; >+} >+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 1cb395dd94e4..07f2ddbf9677 100644 >--- a/init/main.c >+++ b/init/main.c >@@ -1044,6 +1044,7 @@ void start_kernel(void) > print_kernel_cmdline(saved_command_line); > /* parameters may set static keys */ > parse_early_param(); >+ init_arch_has_pmd_leaves(); One more thought here: I don't see why we need boot-time caching. has_transparent_hugepage() does *not* look expensive on the common archs. On x86, it is just a CPU feature check. MIPS is different, yes, only the first call there is more involved ... But if we *really* want caching, couldn't we just do it lazily instead of adding another early boot init step? Something like: bool pgtable_has_pmd_leaves(void) { static int __arch_has_pmd_leaves = -1; if (READ_ONCE(__arch_has_pmd_leaves) < 0) WRITE_ONCE(__arch_has_pmd_leaves, has_transparent_hugepage()); return READ_ONCE(__arch_has_pmd_leaves); } That would avoid depending on parse_early_param() / parse_args() ordering, and it seems much simpler too :) The boot-time init step looks a bit shaky to me ... Thanks, Lance