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[2003:d8:2f35:8a00:42f7:2657:34cc:a51f]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b79c4a2187sm23345507f8f.70.2025.08.06.03.11.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Aug 2025 03:11:35 -0700 (PDT) Message-ID: Date: Wed, 6 Aug 2025 12:11:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 6/7] mm: Optimize mprotect() by PTE batching To: Lorenzo Stoakes , Dev Jain Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@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> <20250718090244.21092-7-dev.jain@arm.com> <7567c594-7588-49e0-8b09-2a591181b24d@redhat.com> <9552ddff-d778-4934-9349-37c7237cbb78@lucifer.local> <54ee1971-d91a-4fe6-90b8-16212c8568d1@redhat.com> <0d52d680-f3d3-454f-8c12-602f650469ab@arm.com> <9cbe9c6a-0013-4239-9347-bf5d43021fe3@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250806_031141_450289_06F8B715 X-CRM114-Status: GOOD ( 22.34 ) 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 06.08.25 11:50, Lorenzo Stoakes wrote: > On Wed, Aug 06, 2025 at 03:07:49PM +0530, Dev Jain wrote: >>>> >>>> You mean in _this_ PTE of the batch right? As we're invoking these >>>> on each part >>>> of the PTE table. >>>> >>>> I mean I guess we can simply do: >>>> >>>>     struct page *first_page = pte_page(ptent); >>>> >>>> Right? >>> >>> Yes, but we should forward the result from vm_normal_page(), which does >>> exactly that for you, and increment the page accordingly as required, >>> just like with the pte we are processing. >> >> Makes sense, so I guess I will have to change the signature of >> prot_numa_skip() >> >> to pass a double ptr to a page instead of folio and derive the folio in the >> caller, >> >> and pass down both the folio and the page to >> set_write_prot_commit_flush_ptes. > > I already don't love how we psas the folio back from there for very dubious > benefit. I really hate the idea of having a struct **page parameter... > > I wonder if we should just have a quick fixup for hotfix, and refine this more > later? This is not an issue in any released kernel, so we can do this properly. We should just remove that nested vm_normal_folio(). Untested, but should give an idea what we can do. diff --git a/mm/mprotect.c b/mm/mprotect.c index 78bded7acf795..4e0a22f7db495 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -120,7 +120,7 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep, static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, pte_t oldpte, pte_t *pte, int target_node, - struct folio **foliop) + struct folio *folio) { struct folio *folio = NULL; bool ret = true; @@ -131,7 +131,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, if (pte_protnone(oldpte)) goto skip; - folio = vm_normal_folio(vma, addr, oldpte); if (!folio) goto skip; @@ -172,8 +171,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, if (folio_use_access_time(folio)) folio_xchg_access_time(folio, jiffies_to_msecs(jiffies)); -skip: - *foliop = folio; return ret; } @@ -231,10 +228,9 @@ static int page_anon_exclusive_sub_batch(int start_idx, int max_len, * retrieve sub-batches. */ static void commit_anon_folio_batch(struct vm_area_struct *vma, - struct folio *folio, unsigned long addr, pte_t *ptep, + struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep, pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb) { - struct page *first_page = folio_page(folio, 0); bool expected_anon_exclusive; int sub_batch_idx = 0; int len; @@ -243,7 +239,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma, expected_anon_exclusive = PageAnonExclusive(first_page + sub_batch_idx); len = page_anon_exclusive_sub_batch(sub_batch_idx, nr_ptes, first_page, expected_anon_exclusive); - prot_commit_flush_ptes(vma, addr, ptep, oldpte, ptent, len, + prot_commit_flush_ptes(vma, addr, ptep, page, oldpte, ptent, len, sub_batch_idx, expected_anon_exclusive, tlb); sub_batch_idx += len; nr_ptes -= len; @@ -251,7 +247,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma, } static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma, - struct folio *folio, unsigned long addr, pte_t *ptep, + struct folio *folio, struct page *page, unsigned long addr, pte_t *ptep, pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb) { bool set_write; @@ -270,7 +266,7 @@ static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma, /* idx = */ 0, set_write, tlb); return; } - commit_anon_folio_batch(vma, folio, addr, ptep, oldpte, ptent, nr_ptes, tlb); + commit_anon_folio_batch(vma, folio, page, addr, ptep, oldpte, ptent, nr_ptes, tlb); } static long change_pte_range(struct mmu_gather *tlb, @@ -305,15 +301,20 @@ static long change_pte_range(struct mmu_gather *tlb, const fpb_t flags = FPB_RESPECT_SOFT_DIRTY | FPB_RESPECT_WRITE; int max_nr_ptes = (end - addr) >> PAGE_SHIFT; struct folio *folio = NULL; + struct page *page; pte_t ptent; + page = vm_normal_folio(vma, addr, oldpte); + if (page) + folio = page_folio(page); + /* * Avoid trapping faults against the zero or KSM * pages. See similar comment in change_huge_pmd. */ if (prot_numa) { int ret = prot_numa_skip(vma, addr, oldpte, pte, - target_node, &folio); + target_node, folio); if (ret) { /* determine batch to skip */ @@ -323,9 +324,6 @@ static long change_pte_range(struct mmu_gather *tlb, } } - if (!folio) - folio = vm_normal_folio(vma, addr, oldpte); - nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags); oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes); @@ -351,7 +349,7 @@ static long change_pte_range(struct mmu_gather *tlb, */ if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && !pte_write(ptent)) - set_write_prot_commit_flush_ptes(vma, folio, + set_write_prot_commit_flush_ptes(vma, folio, page, addr, pte, oldpte, ptent, nr_ptes, tlb); else prot_commit_flush_ptes(vma, addr, pte, oldpte, ptent, -- 2.50.1 -- Cheers, David / dhildenb