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[79.224.245.151]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45862cf0fcbsm23088775e9.0.2025.07.22.09.17.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Jul 2025 09:17:02 -0700 (PDT) Message-ID: Date: Tue, 22 Jul 2025 18:17:01 +0200 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 v3 3/3] khugepaged: Optimize collapse_pte_mapped_thp() by PTE batching To: Dev Jain , akpm@linux-foundation.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250722150559.96465-1-dev.jain@arm.com> <20250722150559.96465-4-dev.jain@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: <20250722150559.96465-4-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 22.07.25 17:05, Dev Jain wrote: > Use PTE batching to optimize collapse_pte_mapped_thp(). > > On arm64, suppose khugepaged is scanning a pte-mapped 2MB THP for collapse. > Then, calling ptep_clear() for every pte will cause a TLB flush for every > contpte block. Instead, clear_ptes() does a contpte_try_unfold_partial() > which will flush the TLB only for the (if any) starting and ending contpte > block, if they partially overlap with the range khugepaged is looking at. > > For all arches, there should be a benefit due to batching atomic operations > on mapcounts due to folio_remove_rmap_ptes() and saving some calls. Please simplify that (and make it less arm specific) like suggested for patch #2. PTE batching has known benefits on all architectures :) > > Note that we do not need to make a change to the check > "if (folio_page(folio, i) != page)"; if i'th page of the folio is equal > to the first page of our batch, then i + 1, .... i + nr_batch_ptes - 1 > pages of the folio will be equal to the corresponding pages of our > batch mapping consecutive pages. Yeah, that must stay to make the comment from "step 1" happy. > > Signed-off-by: Dev Jain > --- > mm/khugepaged.c | 32 ++++++++++++++++++++------------ > 1 file changed, 20 insertions(+), 12 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 63517ef7eafb..1ff0c7dd2be4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1503,15 +1503,16 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr, > int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, > bool install_pmd) > { > + int nr_mapped_ptes = 0, nr_batch_ptes, result = SCAN_FAIL; > struct mmu_notifier_range range; > bool notified = false; > unsigned long haddr = addr & HPAGE_PMD_MASK; > + unsigned long end = haddr + HPAGE_PMD_SIZE; > struct vm_area_struct *vma = vma_lookup(mm, haddr); > struct folio *folio; > pte_t *start_pte, *pte; > pmd_t *pmd, pgt_pmd; > spinlock_t *pml = NULL, *ptl; > - int nr_ptes = 0, result = SCAN_FAIL; > int i; > > mmap_assert_locked(mm); > @@ -1625,11 +1626,15 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, > goto abort; > > /* step 2: clear page table and adjust rmap */ > - for (i = 0, addr = haddr, pte = start_pte; > - i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { > + for (i = 0, addr = haddr, pte = start_pte; i < HPAGE_PMD_NR; > + i += nr_batch_ptes, addr += nr_batch_ptes * PAGE_SIZE, > + pte += nr_batch_ptes) { > + int max_nr_batch_ptes = (end - addr) >> PAGE_SHIFT;> struct page *page; > pte_t ptent = ptep_get(pte); > > + nr_batch_ptes = 1; > + > if (pte_none(ptent)) > continue; > /* > @@ -1643,26 +1648,29 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, > goto abort; > } > page = vm_normal_page(vma, addr, ptent); > + > if (folio_page(folio, i) != page) > goto abort; > > + nr_batch_ptes = folio_pte_batch(folio, pte, ptent, max_nr_batch_ptes); Same comment regarding matching types for folio_pte_batch(), now that we changed that -- unsigned int. > + > /* > * Must clear entry, or a racing truncate may re-remove it. > * TLB flush can be left until pmdp_collapse_flush() does it. > * PTE dirty? Shmem page is already dirty; file is read-only. > */ > - ptep_clear(mm, addr, pte); > - folio_remove_rmap_pte(folio, page, vma); > - nr_ptes++; > + clear_ptes(mm, addr, pte, nr_batch_ptes); > + folio_remove_rmap_ptes(folio, page, nr_batch_ptes, vma); > + nr_mapped_ptes += nr_batch_ptes; > } > > if (!pml) > spin_unlock(ptl); > > /* step 3: set proper refcount and mm_counters. */ > - if (nr_ptes) { > - folio_ref_sub(folio, nr_ptes); > - add_mm_counter(mm, mm_counter_file(folio), -nr_ptes); > + if (nr_mapped_ptes) { > + folio_ref_sub(folio, nr_mapped_ptes); > + add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); > } > > /* step 4: remove empty page table */ > @@ -1695,10 +1703,10 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, > : SCAN_SUCCEED; > goto drop_folio; > abort: > - if (nr_ptes) { > + if (nr_mapped_ptes) { > flush_tlb_mm(mm); > - folio_ref_sub(folio, nr_ptes); > - add_mm_counter(mm, mm_counter_file(folio), -nr_ptes); > + folio_ref_sub(folio, nr_mapped_ptes); > + add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); Doing the TLB flush and adjusting the refcount after dropping the PTL ... interesting. Well, nothing surprises me in khugpaged code anymore. Acked-by: David Hildenbrand -- Cheers, David / dhildenb