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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id k131-20020a816f89000000b0055a416529bbsm1831188ywc.24.2023.05.21.22.27.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 May 2023 22:28:00 -0700 (PDT) Date: Sun, 21 May 2023 22:27:57 -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 , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 30/31] mm/pgtable: delete pmd_trans_unstable() and friends In-Reply-To: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> Message-ID: References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: F3AC380002 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: sdco4uthisfrww8wxyoa8bpxa1qji794 X-HE-Tag: 1684733281-269634 X-HE-Meta: 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 Cybgvl50 CKajb0h+57x6gO6Z/te9lxT9JlC7qBvpBIPebWHIAmhp7XmF/ft3y54Pqv8MB+FR8rqQ7JoPd+R2nuNyreifF0zhmup7EZGbkB9byXx1SbJBkqA/eWxntf3gDfWDEe0jfRMziJ0Zw47IxZSWv5/p7GF8ttq1r11Zab7tiWtn5YGIdAn9mSgCAgWwNdWX9rDszfHyhP326+WAjr2bmm/HFLNixGJvll9OyrjCQbnb0L5TSMVipqq1qTJTu+gTrgxy83qOjFuVLR+SWW+pZYnwzH9EHU7LJjz3yh5Q3SSr3TkzhYrsys3uwa/TFsrKCqxwGg0onfwCJnhPyltnWnjXTEZxZXSDIX3YIJ8tkG+FGtvNTuw4kQB5kh2wnOK1LFs0TTUEMBQlEwrsCLVzvWY8zZENXQ4qUeKIGHSEgxr6FQZ7bfkD4XuGEdfN3NA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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