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(p200300d82f3f4b00ee138c225cc5d169.dip0.t-ipconnect.de. [2003:d8:2f3f:4b00:ee13:8c22:5cc5:d169]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429952cb7dcsm16467040f8f.11.2025.10.27.12.24.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Oct 2025 12:24:41 -0700 (PDT) Message-ID: <276b70aa-9853-40cc-8e7d-e790166706b5@redhat.com> Date: Mon, 27 Oct 2025 20:24:40 +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: [RFC PATCH 1/3] mm: Introduce can_pte_batch_count() for PTEs batch optimization. To: Zhang Qilong , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jannh@google.com, pfalcato@suse.de Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20251027140315.907864-1-zhangqilong3@huawei.com> <20251027140315.907864-2-zhangqilong3@huawei.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20251027140315.907864-2-zhangqilong3@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 27.10.25 15:03, Zhang Qilong wrote: > Currently, the PTEs batch requires folio access, with the maximum > quantity limited to the PFNs contained within the folio. However, > in certain case (such as mremap_folio_pte_batch and mincore_pte_range), > accessing the folio is unnecessary and expensive. > > For scenarios that do not require folio access, this patch introduces > can_pte_batch_count(). With contiguous physical addresses and identical > PTE attribut bits, we can now process more page table entries at once, > in batch, not just limited to entries mapped within a single folio. On > the other hand, it avoid the folio access. > > Signed-off-by: Zhang Qilong > --- > mm/internal.h | 76 +++++++++++++++++++++++++++++++++++++++------------ > 1 file changed, 58 insertions(+), 18 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 1561fc2ff5b8..92034ca9092d 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -233,61 +233,62 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) > pte = pte_wrprotect(pte); > return pte_mkold(pte); > } > > /** > - * folio_pte_batch_flags - detect a PTE batch for a large folio > - * @folio: The large folio to detect a PTE batch for. > + * can_pte_batch_count - detect a PTE batch in range [ptep, to ptep + max_nr) I really don't like the name. Maybe it's just pte_batch(). > * @vma: The VMA. Only relevant with FPB_MERGE_WRITE, otherwise can be NULL. > * @ptep: Page table pointer for the first entry. > * @ptentp: Pointer to a COPY of the first page table entry whose flags this > * function updates based on @flags if appropriate. > * @max_nr: The maximum number of table entries to consider. > * @flags: Flags to modify the PTE batch semantics. > * > - * Detect a PTE batch: consecutive (present) PTEs that map consecutive > - * pages of the same large folio in a single VMA and a single page table. > + * This interface is designed for this case that do not require folio access. > + * If folio consideration is needed, please call folio_pte_batch_flags instead. > + * > + * Detect a PTE batch: consecutive (present) PTEs that map consecutive pages > + * in a single VMA and a single page table. > * > * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN, > * the accessed bit, writable bit, dirty bit (unless FPB_RESPECT_DIRTY is set) > * and soft-dirty bit (unless FPB_RESPECT_SOFT_DIRTY is set). > * > - * @ptep must map any page of the folio. max_nr must be at least one and > + * @ptep point to the first entry in range, max_nr must be at least one and > * must be limited by the caller so scanning cannot exceed a single VMA and > * a single page table. > * > * Depending on the FPB_MERGE_* flags, the pte stored at @ptentp will > * be updated: it's crucial that a pointer to a COPY of the first > * page table entry, obtained through ptep_get(), is provided as @ptentp. > * > - * This function will be inlined to optimize based on the input parameters; > - * consider using folio_pte_batch() instead if applicable. > + * The following folio_pte_batch_flags() deal with PTEs that mapped in a > + * single folio. However can_pte_batch_count has the capability to handle > + * PTEs that mapped in consecutive folios. If flags is not set, it will ignore > + * the accessed, writable and dirty bits. Once the flags is set, the respect > + * bit(s) will be compared in pte_same(), if the advanced pte_batch_hint() > + * respect pte bit is different, pte_same() will return false and break. This > + * ensures the correctness of handling multiple folio PTEs. > + * > + * This function will be inlined to optimize based on the input parameters. > * > * Return: the number of table entries in the batch. > */ I recall trouble if we try batching across folios: commit 7b08b74f3d99f6b801250683c751d391128799ec (tag: mm-hotfixes-stable-2025-05-10-14-23) Author: Petr Vaněk Date: Fri May 2 23:50:19 2025 +0200 mm: fix folio_pte_batch() on XEN PV On XEN PV, folio_pte_batch() can incorrectly batch beyond the end of a folio due to a corner case in pte_advance_pfn(). Specifically, when the PFN following the folio maps to an invalidated MFN, expected_pte = pte_advance_pfn(expected_pte, nr); produces a pte_none(). If the actual next PTE in memory is also pte_none(), the pte_same() succeeds, if (!pte_same(pte, expected_pte)) break; the loop is not broken, and batching continues into unrelated memory. ... -- Cheers David / dhildenb