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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BD93C7EE29 for ; Fri, 9 Jun 2023 01:51:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237994AbjFIBu4 (ORCPT ); Thu, 8 Jun 2023 21:50:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52598 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237975AbjFIBux (ORCPT ); Thu, 8 Jun 2023 21:50:53 -0400 Received: from mail-yb1-xb2d.google.com (mail-yb1-xb2d.google.com [IPv6:2607:f8b0:4864:20::b2d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C14721BF0 for ; Thu, 8 Jun 2023 18:50:49 -0700 (PDT) Received: by mail-yb1-xb2d.google.com with SMTP id 3f1490d57ef6-bb167972cffso1373658276.1 for ; Thu, 08 Jun 2023 18:50:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1686275449; x=1688867449; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=5QGRbISmNdiSrcRCSB3pJg16AgA7v+5ZDTS/B09Kn8o=; b=VYBwsG1BtIkMXYG/EqMPmNqaJtObBxLa0DzVTT5ka0MvcTVzYnyBd4s72c34jeMJWZ xJedOpJC62Y06znAOr56dfhffB75a2S0AEDjwGdBtR8M50W2ZRRdIZBxB+7WBisOZrKT nPmJFCweF3RKUaSLr026wSZQ2QVhzWfX9ltBG3Uq6D/Lj/QnQ1Y+MBLl1GEWPRjympq5 k7E6IjPRJAuuYRzzFwPhEP7q5GuBMvHkMBcEHG6JFmqkrVIuIbku6yQIyNpLr2Fx94UY CJ6aDp4I29QQMn44W1tjU0XjRP5XR9NluCQv+G6gcGOq9aMokdcjYhjrO1zsvgIIBXRP l9eQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686275449; x=1688867449; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=5QGRbISmNdiSrcRCSB3pJg16AgA7v+5ZDTS/B09Kn8o=; b=PBitS/xhWz1cVDi/iqdnibfEjgQxOZfjOVJwS+RpXYyqsyVnSASjiMMbXwds8Mlba7 brOsDoNoGJsJyBwPZFyEsbIHNAa6nRMCNzTGJ+uZ1+wcItytPS3u0zs/QPNCJL8y8IeY /tXXy3w8lc0PA7Z0YUZ6DyJawnD2Zel8aeUfmpKs7+bIZzCMOv/QziKq+FHxGzQ65zX0 Mf9RNmZymEe+O7kGcPPsCHkjhAswLkznNJZYW9Lpl/Rb7P4VKfBUHSihU4OksrHHHnuA uaZ6NHPK3rhfjqhkw0rkhc8sQm/YqUFMpAssB0eI6q1goq5Wtehrc3Pypv5OfNmJGkq0 GLKw== X-Gm-Message-State: AC+VfDxMlZx3SlHX/Srud9+GLqjUfU2KxxB3a+ZkFG4pdOtaygkdgM4K sahIJ8F6JeqWcbqASLctw0P9+A== X-Google-Smtp-Source: ACHHUZ7rkKxLDUXb7gVbThinQJUAuYEpzA2mTjY1b2VjU6hE71QC6+GRYBvyPmvE/ofxxSjMXUupyg== X-Received: by 2002:a25:4103:0:b0:ba8:8779:667 with SMTP id o3-20020a254103000000b00ba887790667mr1159827yba.41.1686275448723; Thu, 08 Jun 2023 18:50:48 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id n11-20020a25400b000000b00bb393903508sm622475yba.14.2023.06.08.18.50.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jun 2023 18:50:47 -0700 (PDT) Date: Thu, 8 Jun 2023 18:50:37 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 30/32] mm/pgtable: delete pmd_trans_unstable() and friends In-Reply-To: Message-ID: <5abdab3-3136-b42e-274d-9c6281bfb79@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Delete pmd_trans_unstable, pmd_none_or_trans_huge_or_clear_bad() and pmd_devmap_trans_unstable(), all now unused. With mixed feelings, delete all the comments on pmd_trans_unstable(). That was very good documentation of a subtle state, and this series does not even eliminate that state: but rather, normalizes and extends it, asking pte_offset_map[_lock]() callers to anticipate failure, without regard for whether mmap_read_lock() or mmap_write_lock() is held. Retain pud_trans_unstable(), which has one use in __handle_mm_fault(), but delete its equivalent pud_none_or_trans_huge_or_dev_or_clear_bad(). While there, move the default arch_needs_pgtable_deposit() definition up near where pgtable_trans_huge_deposit() and withdraw() are declared. Signed-off-by: Hugh Dickins --- include/linux/pgtable.h | 103 +++------------------------------------- mm/khugepaged.c | 4 -- 2 files changed, 7 insertions(+), 100 deletions(-) diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 3fabbb018557..a1326e61d7ee 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -599,6 +599,10 @@ extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp, extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp); #endif +#ifndef arch_needs_pgtable_deposit +#define arch_needs_pgtable_deposit() (false) +#endif + #ifdef CONFIG_TRANSPARENT_HUGEPAGE /* * This is an implementation of pmdp_establish() that is only suitable for an @@ -1300,9 +1304,10 @@ static inline int pud_trans_huge(pud_t pud) } #endif -/* See pmd_none_or_trans_huge_or_clear_bad for discussion. */ -static inline int pud_none_or_trans_huge_or_dev_or_clear_bad(pud_t *pud) +static inline int pud_trans_unstable(pud_t *pud) { +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \ + defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) pud_t pudval = READ_ONCE(*pud); if (pud_none(pudval) || pud_trans_huge(pudval) || pud_devmap(pudval)) @@ -1311,104 +1316,10 @@ static inline int pud_none_or_trans_huge_or_dev_or_clear_bad(pud_t *pud) pud_clear_bad(pud); return 1; } - return 0; -} - -/* See pmd_trans_unstable for discussion. */ -static inline int pud_trans_unstable(pud_t *pud) -{ -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \ - defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) - return pud_none_or_trans_huge_or_dev_or_clear_bad(pud); -#else - return 0; #endif -} - -#ifndef arch_needs_pgtable_deposit -#define arch_needs_pgtable_deposit() (false) -#endif -/* - * This function is meant to be used by sites walking pagetables with - * the mmap_lock held in read mode to protect against MADV_DONTNEED and - * transhuge page faults. MADV_DONTNEED can convert a transhuge pmd - * into a null pmd and the transhuge page fault can convert a null pmd - * into an hugepmd or into a regular pmd (if the hugepage allocation - * fails). While holding the mmap_lock in read mode the pmd becomes - * stable and stops changing under us only if it's not null and not a - * transhuge pmd. When those races occurs and this function makes a - * difference vs the standard pmd_none_or_clear_bad, the result is - * undefined so behaving like if the pmd was none is safe (because it - * can return none anyway). The compiler level barrier() is critically - * important to compute the two checks atomically on the same pmdval. - * - * For 32bit kernels with a 64bit large pmd_t this automatically takes - * care of reading the pmd atomically to avoid SMP race conditions - * against pmd_populate() when the mmap_lock is hold for reading by the - * caller (a special atomic read not done by "gcc" as in the generic - * version above, is also needed when THP is disabled because the page - * fault can populate the pmd from under us). - */ -static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd) -{ - pmd_t pmdval = pmdp_get_lockless(pmd); - /* - * !pmd_present() checks for pmd migration entries - * - * The complete check uses is_pmd_migration_entry() in linux/swapops.h - * But using that requires moving current function and pmd_trans_unstable() - * to linux/swapops.h to resolve dependency, which is too much code move. - * - * !pmd_present() is equivalent to is_pmd_migration_entry() currently, - * because !pmd_present() pages can only be under migration not swapped - * out. - * - * pmd_none() is preserved for future condition checks on pmd migration - * entries and not confusing with this function name, although it is - * redundant with !pmd_present(). - */ - if (pmd_none(pmdval) || pmd_trans_huge(pmdval) || - (IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION) && !pmd_present(pmdval))) - return 1; - if (unlikely(pmd_bad(pmdval))) { - pmd_clear_bad(pmd); - return 1; - } return 0; } -/* - * This is a noop if Transparent Hugepage Support is not built into - * the kernel. Otherwise it is equivalent to - * pmd_none_or_trans_huge_or_clear_bad(), and shall only be called in - * places that already verified the pmd is not none and they want to - * walk ptes while holding the mmap sem in read mode (write mode don't - * need this). If THP is not enabled, the pmd can't go away under the - * code even if MADV_DONTNEED runs, but if THP is enabled we need to - * run a pmd_trans_unstable before walking the ptes after - * split_huge_pmd returns (because it may have run when the pmd become - * null, but then a page fault can map in a THP and not a regular page). - */ -static inline int pmd_trans_unstable(pmd_t *pmd) -{ -#ifdef CONFIG_TRANSPARENT_HUGEPAGE - return pmd_none_or_trans_huge_or_clear_bad(pmd); -#else - return 0; -#endif -} - -/* - * the ordering of these checks is important for pmds with _page_devmap set. - * if we check pmd_trans_unstable() first we will trip the bad_pmd() check - * inside of pmd_none_or_trans_huge_or_clear_bad(). this will end up correctly - * returning 1 but not before it spams dmesg with the pmd_clear_bad() output. - */ -static inline int pmd_devmap_trans_unstable(pmd_t *pmd) -{ - return pmd_devmap(*pmd) || pmd_trans_unstable(pmd); -} - #ifndef CONFIG_NUMA_BALANCING /* * Technically a PTE can be PROTNONE even when not doing NUMA balancing but diff --git a/mm/khugepaged.c b/mm/khugepaged.c index c11db2e78e95..1083f0e38a07 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -946,10 +946,6 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, return SCAN_SUCCEED; } -/* - * See pmd_trans_unstable() for how the result may change out from - * underneath us, even if we hold mmap_lock in read. - */ static int find_pmd_or_thp_or_none(struct mm_struct *mm, unsigned long address, pmd_t **pmd) -- 2.35.3