From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 87137288C33 for ; Tue, 22 Jul 2025 11:26:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753183575; cv=none; b=aMOyFqtB/Vubq5jGPdsoZHo+2/IDkJk+VPbzAVUS74Ayvo2582E6BO/gIyWP5+4IyajaEodoXFEOlkZPuSXFWnxDAyXe3xK1SY5eYoK+aKz0SujHZbQa4UFy+O02dAFHpVk9tj1iwBTXphSLCux7+LhEIScdXP2KAKB5OFOuaRw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753183575; c=relaxed/simple; bh=lbkkBmS+V+CmfSsRflihVrZqd7jwmECrPn0vHuEYzNs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=vBeMO/g8AEOwBKgOVRlAFSWyXPCGbn+ies2ZHOi05FAl18mm8Bj9qwtQ597eTD3tM7P3X7wg9B6DG8ltz1awgF1n3aGp3vEHhU1AAgatAApPrUMWFUjH5MGmRkVCaQUtgDYi87p/XX12y58cEmkZVnuC9rSnOZKmsOxHGuTYGHg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 5BE64152B; Tue, 22 Jul 2025 04:26:07 -0700 (PDT) Received: from [10.1.30.167] (XHFQ2J9959.cambridge.arm.com [10.1.30.167]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD9293F66E; Tue, 22 Jul 2025 04:26:09 -0700 (PDT) Message-ID: <3b105623-95c2-4d4b-b49f-dd087eaa652b@arm.com> Date: Tue, 22 Jul 2025 12:26:08 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/7] 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: <20250718090244.21092-1-dev.jain@arm.com> <20250718090244.21092-3-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250718090244.21092-3-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 18/07/2025 10:02, Dev Jain wrote: > For the MM_CP_PROT_NUMA skipping case, observe that, if we skip an > iteration due to the underlying folio satisfying any of the skip > conditions, then for all subsequent ptes which map the same folio, the > iteration will be skipped for them too. Therefore, we can optimize > by using folio_pte_batch() to batch skip the iterations. > > Use prot_numa_skip() introduced in the previous patch to determine whether > we need to skip the iteration. Change its signature to have a double > pointer to a folio, which will be used by mprotect_folio_pte_batch() to > determine the number of iterations we can safely skip. > > Signed-off-by: Dev Jain LGTM: Reviewed-by: Ryan Roberts > --- > mm/mprotect.c | 55 +++++++++++++++++++++++++++++++++++++++------------ > 1 file changed, 42 insertions(+), 13 deletions(-) > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 2a9c73bd0778..97adc62c50ab 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -83,28 +83,43 @@ 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, pte_t *ptep, > + pte_t pte, int max_nr_ptes) > +{ > + /* No underlying folio, so cannot batch */ > + if (!folio) > + return 1; > + > + if (!folio_test_large(folio)) > + return 1; > + > + return folio_pte_batch(folio, ptep, pte, max_nr_ptes); > +} > + > static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, > - pte_t oldpte, pte_t *pte, int target_node) > + pte_t oldpte, pte_t *pte, int target_node, > + struct folio **foliop) > { > - struct folio *folio; > + struct folio *folio = NULL; > + bool ret = true; > bool toptier; > int nid; > > /* Avoid TLB flush if possible */ > if (pte_protnone(oldpte)) > - return true; > + goto skip; > > folio = vm_normal_folio(vma, addr, oldpte); > if (!folio) > - return true; > + goto skip; > > if (folio_is_zone_device(folio) || folio_test_ksm(folio)) > - return true; > + goto skip; > > /* Also skip shared copy-on-write pages */ > if (is_cow_mapping(vma->vm_flags) && > (folio_maybe_dma_pinned(folio) || folio_maybe_mapped_shared(folio))) > - return true; > + goto skip; > > /* > * While migration can move some dirty pages, > @@ -112,7 +127,7 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, > * context. > */ > if (folio_is_file_lru(folio) && folio_test_dirty(folio)) > - return true; > + goto skip; > > /* > * Don't mess with PTEs if page is already on the node > @@ -120,7 +135,7 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, > */ > nid = folio_nid(folio); > if (target_node == nid) > - return true; > + goto skip; > > toptier = node_is_toptier(nid); > > @@ -129,11 +144,15 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, > * balancing is disabled > */ > if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) && toptier) > - return true; > + goto skip; > > + ret = false; > if (folio_use_access_time(folio)) > folio_xchg_access_time(folio, jiffies_to_msecs(jiffies)); > - return false; > + > +skip: > + *foliop = folio; > + return ret; > } > > static long change_pte_range(struct mmu_gather *tlb, > @@ -147,6 +166,7 @@ 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); > @@ -161,8 +181,11 @@ 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; > pte_t ptent; > > /* > @@ -170,9 +193,15 @@ static long change_pte_range(struct mmu_gather *tlb, > * pages. See similar comment in change_huge_pmd. > */ > if (prot_numa) { > - if (prot_numa_skip(vma, addr, oldpte, pte, > - target_node)) > + int ret = prot_numa_skip(vma, addr, oldpte, pte, > + target_node, &folio); > + if (ret) { > + > + /* determine batch to skip */ > + nr_ptes = mprotect_folio_pte_batch(folio, > + pte, oldpte, max_nr_ptes); > continue; > + } > } > > oldpte = ptep_modify_prot_start(vma, addr, pte); > @@ -289,7 +318,7 @@ 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); >