From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BAF473148AC; Wed, 21 Jan 2026 18:35:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769020539; cv=none; b=bTQbZVZJQtX1b2qcdNPPu3BRd9tjwQKYhlZziWroTHKUhnAkFGYVh2nY/ftf2fwPwvEdzCx0RA/ycskXreLzmwftjzpA/isCkcUlcbvytjESwWFO/9L+3Lg1kvJg1wugVD1utjmmySJxwtWOH3905gMCe7mvB1iHfMxaKJloFE8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769020539; c=relaxed/simple; bh=MF8TjWZlr7E4gCsPW4TKsLbaZD4njkf9Vcdx+ms4MLA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eRRvzW5nUBqxwa1o2O/t2xa2mRQw16OMiqgtwFv6PDbESxnqQZ59DiZaNCcvzQsYnMBpvzkjsMRuwEJ/KVQ67EfH9ZzS9CiRZ+KpNRZMAddBLoxluwfmKBCSqmYdTN1UggsIH12Ck2pGk3L8FPvfwtM2nSUGgwUz3Y+fqPKVFWQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=qUy8BvYc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="qUy8BvYc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D27FEC4CEF1; Wed, 21 Jan 2026 18:35:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769020539; bh=MF8TjWZlr7E4gCsPW4TKsLbaZD4njkf9Vcdx+ms4MLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qUy8BvYcObTFyubMMh/j+TcNNlahMAmSeQh+Fw6bRzPA4gXGXxGMVxD7hzdyxAEn1 oyqPhIuIM3f1qUGed2iTue+4t+WR09Ujcs6CXVzBehR1oEW7hoHxGb03Cu88ONoHEG Cf0Tb9DyY3vbGpugCY2LQAlj02jQCVRZX5vIA3yQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Dave Hansen , Lu Baolu , Jason Gunthorpe , Kevin Tian , David Hildenbrand , "Mike Rapoport (Microsoft)" , Alistair Popple , Andy Lutomirski , Borislav Betkov , Ingo Molnar , Jann Horn , Jean-Philippe Brucker , Joerg Roedel , Liam Howlett , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Peter Zijlstra , Robin Murohy , Thomas Gleinxer , "Uladzislau Rezki (Sony)" , Vasant Hegde , Vinicius Costa Gomes , Vlastimil Babka , Will Deacon , Yi Lai , Andrew Morton Subject: [PATCH 6.18 189/198] mm: introduce deferred freeing for kernel page tables Date: Wed, 21 Jan 2026 19:16:57 +0100 Message-ID: <20260121181425.359723354@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260121181418.537774329@linuxfoundation.org> References: <20260121181418.537774329@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dave Hansen commit 5ba2f0a1556479638ac11a3c201421f5515e89f5 upstream. This introduces a conditional asynchronous mechanism, enabled by CONFIG_ASYNC_KERNEL_PGTABLE_FREE. When enabled, this mechanism defers the freeing of pages that are used as page tables for kernel address mappings. These pages are now queued to a work struct instead of being freed immediately. This deferred freeing allows for batch-freeing of page tables, providing a safe context for performing a single expensive operation (TLB flush) for a batch of kernel page tables instead of performing that expensive operation for each page table. Link: https://lkml.kernel.org/r/20251022082635.2462433-8-baolu.lu@linux.intel.com Signed-off-by: Dave Hansen Signed-off-by: Lu Baolu Reviewed-by: Jason Gunthorpe Reviewed-by: Kevin Tian Acked-by: David Hildenbrand Acked-by: Mike Rapoport (Microsoft) Cc: Alistair Popple Cc: Andy Lutomirski Cc: Borislav Betkov Cc: Ingo Molnar Cc: Jann Horn Cc: Jean-Philippe Brucker Cc: Joerg Roedel Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Peter Zijlstra Cc: Robin Murohy Cc: Thomas Gleinxer Cc: "Uladzislau Rezki (Sony)" Cc: Vasant Hegde Cc: Vinicius Costa Gomes Cc: Vlastimil Babka Cc: Will Deacon Cc: Yi Lai Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- include/linux/mm.h | 16 +++++++++++++--- mm/Kconfig | 3 +++ mm/pgtable-generic.c | 37 +++++++++++++++++++++++++++++++++++++ 3 files changed, 53 insertions(+), 3 deletions(-) --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3038,6 +3038,14 @@ static inline void __pagetable_free(stru __free_pages(page, compound_order(page)); } +#ifdef CONFIG_ASYNC_KERNEL_PGTABLE_FREE +void pagetable_free_kernel(struct ptdesc *pt); +#else +static inline void pagetable_free_kernel(struct ptdesc *pt) +{ + __pagetable_free(pt); +} +#endif /** * pagetable_free - Free pagetables * @pt: The page table descriptor @@ -3047,10 +3055,12 @@ static inline void __pagetable_free(stru */ static inline void pagetable_free(struct ptdesc *pt) { - if (ptdesc_test_kernel(pt)) + if (ptdesc_test_kernel(pt)) { ptdesc_clear_kernel(pt); - - __pagetable_free(pt); + pagetable_free_kernel(pt); + } else { + __pagetable_free(pt); + } } #if defined(CONFIG_SPLIT_PTE_PTLOCKS) --- a/mm/Kconfig +++ b/mm/Kconfig @@ -915,6 +915,9 @@ config HAVE_GIGANTIC_FOLIOS def_bool (HUGETLB_PAGE && ARCH_HAS_GIGANTIC_PAGE) || \ (ZONE_DEVICE && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) +config ASYNC_KERNEL_PGTABLE_FREE + def_bool n + # TODO: Allow to be enabled without THP config ARCH_SUPPORTS_HUGE_PFNMAP def_bool n --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -406,3 +406,40 @@ again: pte_unmap_unlock(pte, ptl); goto again; } + +#ifdef CONFIG_ASYNC_KERNEL_PGTABLE_FREE +static void kernel_pgtable_work_func(struct work_struct *work); + +static struct { + struct list_head list; + /* protect above ptdesc lists */ + spinlock_t lock; + struct work_struct work; +} kernel_pgtable_work = { + .list = LIST_HEAD_INIT(kernel_pgtable_work.list), + .lock = __SPIN_LOCK_UNLOCKED(kernel_pgtable_work.lock), + .work = __WORK_INITIALIZER(kernel_pgtable_work.work, kernel_pgtable_work_func), +}; + +static void kernel_pgtable_work_func(struct work_struct *work) +{ + struct ptdesc *pt, *next; + LIST_HEAD(page_list); + + spin_lock(&kernel_pgtable_work.lock); + list_splice_tail_init(&kernel_pgtable_work.list, &page_list); + spin_unlock(&kernel_pgtable_work.lock); + + list_for_each_entry_safe(pt, next, &page_list, pt_list) + __pagetable_free(pt); +} + +void pagetable_free_kernel(struct ptdesc *pt) +{ + spin_lock(&kernel_pgtable_work.lock); + list_add(&pt->pt_list, &kernel_pgtable_work.list); + spin_unlock(&kernel_pgtable_work.lock); + + schedule_work(&kernel_pgtable_work.work); +} +#endif