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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 56ABDC8302D for ; Mon, 30 Jun 2025 09:48:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=1cgzhjY+K2VUhAwhVVQwZIeHki+ZMFQ5dSzLLVQN7yw=; b=uwwXK5Ufp+eRz5ICwF0MFICrHp +Z+2MnQpvduh8w9o61lCOdo5EtJSlFKqnafW8dkYBApeos/j9i1Lt8ymAp7EV3Q6n8JXbqK20EYl8 qCMgxhFWjluJUME3SGUMkIuM5keLjACJnsbe6irTVu0O/5yG7fidA30u/XQqXmX1Zu0P7JhCn39x6 mv8ygfyTia8i9HxvItapw7tV3drzJVLUFV5yrjvNsL/DMBxGuTJ9wySGODa+y6IjSE2Q2Q5ihyCca Zcp0cIYRY0i8XTcKg0fYoU8iW9GlB8KhuEEgFBwe0uQMM50V0dtNoQLr7HcdGdd1Ip5ZYyJ+lA03p k14Scnbg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uWB87-00000001nEq-08bL; Mon, 30 Jun 2025 09:48:51 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uWB2Q-00000001mHy-0aOP for linux-arm-kernel@lists.infradead.org; Mon, 30 Jun 2025 09:42:59 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 652AC1D34; Mon, 30 Jun 2025 02:42:39 -0700 (PDT) Received: from [10.1.34.165] (XHFQ2J9959.cambridge.arm.com [10.1.34.165]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3E6DB3F6A8; Mon, 30 Jun 2025 02:42:50 -0700 (PDT) Message-ID: Date: Mon, 30 Jun 2025 10:42:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/4] mm: Optimize mprotect() for MM_CP_PROT_NUMA by batch-skipping PTEs Content-Language: en-GB To: Dev Jain , akpm@linux-foundation.org Cc: david@redhat.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250628113435.46678-1-dev.jain@arm.com> <20250628113435.46678-2-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250628113435.46678-2-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250630_024258_266544_F9EDC945 X-CRM114-Status: GOOD ( 29.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 28/06/2025 12:34, Dev Jain wrote: > In case of prot_numa, there are various cases in which we can skip to the > next iteration. Since the skip condition is based on the folio and not > the PTEs, we can skip a PTE batch. Additionally refactor all of this > into a new function to clean up the existing code. > > Signed-off-by: Dev Jain > --- > mm/mprotect.c | 134 ++++++++++++++++++++++++++++++++------------------ > 1 file changed, 87 insertions(+), 47 deletions(-) > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 88709c01177b..af10a7fbe6b8 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -83,6 +83,83 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, > return pte_dirty(pte); > } > > +static int mprotect_folio_pte_batch(struct folio *folio, unsigned long addr, > + pte_t *ptep, pte_t pte, int max_nr_ptes) > +{ > + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; > + > + if (!folio || !folio_test_large(folio) || (max_nr_ptes == 1)) The !folio check wasn't in the previous version. Why is it needed now? > + return 1; > + > + return folio_pte_batch(folio, addr, ptep, pte, max_nr_ptes, flags, > + NULL, NULL, NULL); > +} > + > +static int prot_numa_skip_ptes(struct folio **foliop, struct vm_area_struct *vma, > + unsigned long addr, pte_t oldpte, pte_t *pte, int target_node, > + int max_nr_ptes) > +{ > + struct folio *folio = NULL; > + int nr_ptes = 1; > + bool toptier; > + int nid; > + > + /* Avoid TLB flush if possible */ > + if (pte_protnone(oldpte)) > + goto skip_batch; > + > + folio = vm_normal_folio(vma, addr, oldpte); > + if (!folio) > + goto skip_batch; > + > + if (folio_is_zone_device(folio) || folio_test_ksm(folio)) > + goto skip_batch; > + > + /* Also skip shared copy-on-write pages */ > + if (is_cow_mapping(vma->vm_flags) && > + (folio_maybe_dma_pinned(folio) || folio_maybe_mapped_shared(folio))) > + goto skip_batch; > + > + /* > + * While migration can move some dirty pages, > + * it cannot move them all from MIGRATE_ASYNC > + * context. > + */ > + if (folio_is_file_lru(folio) && folio_test_dirty(folio)) > + goto skip_batch; > + > + /* > + * Don't mess with PTEs if page is already on the node > + * a single-threaded process is running on. > + */ > + nid = folio_nid(folio); > + if (target_node == nid) > + goto skip_batch; > + > + toptier = node_is_toptier(nid); > + > + /* > + * Skip scanning top tier node if normal numa > + * balancing is disabled > + */ > + if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) && toptier) > + goto skip_batch; > + > + if (folio_use_access_time(folio)) { > + folio_xchg_access_time(folio, jiffies_to_msecs(jiffies)); > + > + /* Do not skip in this case */ > + nr_ptes = 0; > + goto out; This doesn't smell right... perhaps I'm not understanding the logic. Why do you return nr_ptes = 0 if you end up in this conditional, but nr_ptes = 1 if you don't take this conditional? I think you want to return nr_ptes == 0 for both cases?... > + } > + > +skip_batch: > + nr_ptes = mprotect_folio_pte_batch(folio, addr, pte, oldpte, max_nr_ptes); > +out: > + *foliop = folio; > + return nr_ptes; > +} > + > static long change_pte_range(struct mmu_gather *tlb, > struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, > unsigned long end, pgprot_t newprot, unsigned long cp_flags) > @@ -94,6 +171,7 @@ static long change_pte_range(struct mmu_gather *tlb, > bool prot_numa = cp_flags & MM_CP_PROT_NUMA; > bool uffd_wp = cp_flags & MM_CP_UFFD_WP; > bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; > + int nr_ptes; > > tlb_change_page_size(tlb, PAGE_SIZE); > pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > @@ -108,8 +186,11 @@ static long change_pte_range(struct mmu_gather *tlb, > flush_tlb_batched_pending(vma->vm_mm); > arch_enter_lazy_mmu_mode(); > do { > + nr_ptes = 1; > oldpte = ptep_get(pte); > if (pte_present(oldpte)) { > + int max_nr_ptes = (end - addr) >> PAGE_SHIFT; > + struct folio *folio = NULL; > pte_t ptent; > > /* > @@ -117,53 +198,12 @@ static long change_pte_range(struct mmu_gather *tlb, > * pages. See similar comment in change_huge_pmd. > */ > if (prot_numa) { > - struct folio *folio; > - int nid; > - bool toptier; > - > - /* Avoid TLB flush if possible */ > - if (pte_protnone(oldpte)) > - continue; > - > - folio = vm_normal_folio(vma, addr, oldpte); > - if (!folio || folio_is_zone_device(folio) || > - folio_test_ksm(folio)) > - continue; > - > - /* Also skip shared copy-on-write pages */ > - if (is_cow_mapping(vma->vm_flags) && > - (folio_maybe_dma_pinned(folio) || > - folio_maybe_mapped_shared(folio))) > - continue; > - > - /* > - * While migration can move some dirty pages, > - * it cannot move them all from MIGRATE_ASYNC > - * context. > - */ > - if (folio_is_file_lru(folio) && > - folio_test_dirty(folio)) > - continue; > - > - /* > - * Don't mess with PTEs if page is already on the node > - * a single-threaded process is running on. > - */ > - nid = folio_nid(folio); > - if (target_node == nid) > - continue; > - toptier = node_is_toptier(nid); > - > - /* > - * Skip scanning top tier node if normal numa > - * balancing is disabled > - */ > - if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) && > - toptier) > + nr_ptes = prot_numa_skip_ptes(&folio, vma, > + addr, oldpte, pte, > + target_node, > + max_nr_ptes); > + if (nr_ptes) > continue; ...But now here nr_ptes == 0 for the "don't skip" case, so won't you process that PTE twice because while (pte += nr_ptes, ...) won't advance it? Suggest forcing nr_ptes = 1 after this conditional "continue"? Thanks, Ryan > - if (folio_use_access_time(folio)) > - folio_xchg_access_time(folio, > - jiffies_to_msecs(jiffies)); > } > > oldpte = ptep_modify_prot_start(vma, addr, pte); > @@ -280,7 +320,7 @@ static long change_pte_range(struct mmu_gather *tlb, > pages++; > } > } > - } while (pte++, addr += PAGE_SIZE, addr != end); > + } while (pte += nr_ptes, addr += nr_ptes * PAGE_SIZE, addr != end); > arch_leave_lazy_mmu_mode(); > pte_unmap_unlock(pte - 1, ptl); >