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[2003:d8:2f02:2900:f54f:bad7:c5f4:9404]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eae963f2bsm16809290f8f.18.2025.04.16.01.22.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Apr 2025 01:22:02 -0700 (PDT) Message-ID: <019d1c4a-ffd0-4602-b2ba-cf07379dab17@redhat.com> Date: Wed, 16 Apr 2025 10:22:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mempolicy: Optimize queue_folios_pte_range by PTE batching To: Baolin Wang , Dev Jain , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, hughd@google.com, vishal.moola@gmail.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250416053048.96479-1-dev.jain@arm.com> <7f96283b-11b3-49ee-9d2d-5ad977325cb0@linux.alibaba.com> From: David Hildenbrand 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/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <7f96283b-11b3-49ee-9d2d-5ad977325cb0@linux.alibaba.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: vyVecppvFCHSfVZpJG4oPgpmcoYpDIDKOPtB7rHqeV4_1744791724 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: aqb5muu8wkm5mu4nhkzbg7dw1xwr1acn X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1DCBC18000B X-Rspam-User: X-HE-Tag: 1744791728-371810 X-HE-Meta: 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 bN0F79bZ vt9I/MrsEPQVFUWkJtbVvlkix4LwmuzeZdmf/titAdFXYH+CDpdNHNmzUF9/HkAeI33bZs5SPzIoq/gP1xtXThspyFKycfJo9FgxV2cI6AgefGYJmCsIIrt0hMf7q+06nBtJdNbrGTIQh9Xp5+QVPBO8WkXDFOKV7f5lbF1gi9CkN4PxZm72QTsrUyFeFm6lKeti5 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16.04.25 08:32, Baolin Wang wrote: > > > On 2025/4/16 13:30, Dev Jain wrote: >> After the check for queue_folio_required(), the code only cares about the >> folio in the for loop, i.e the PTEs are redundant. Therefore, optimize >> this loop by skipping over a PTE batch mapping the same folio. >> >> With a test program migrating pages of the calling process, which includes >> a mapped VMA of size 4GB with pte-mapped large folios of order-9, and >> migrating once back and forth node-0 and node-1, the average execution >> time reduces from 7.5 to 4 seconds, giving an approx 47% speedup. >> >> v2->v3: >> - Don't use assignment in if condition >> >> v1->v2: >> - Follow reverse xmas tree declarations >> - Don't initialize nr >> - Move folio_pte_batch() immediately after retrieving a normal folio >> - increment nr_failed in one shot >> >> Acked-by: David Hildenbrand >> Signed-off-by: Dev Jain >> --- >> mm/mempolicy.c | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index b28a1e6ae096..4d2dc8b63965 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -566,6 +566,7 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk) >> static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, >> unsigned long end, struct mm_walk *walk) >> { >> + const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; >> struct vm_area_struct *vma = walk->vma; >> struct folio *folio; >> struct queue_pages *qp = walk->private; >> @@ -573,6 +574,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, >> pte_t *pte, *mapped_pte; >> pte_t ptent; >> spinlock_t *ptl; >> + int max_nr, nr; >> >> ptl = pmd_trans_huge_lock(pmd, vma); >> if (ptl) { >> @@ -586,7 +588,9 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, >> walk->action = ACTION_AGAIN; >> return 0; >> } >> - for (; addr != end; pte++, addr += PAGE_SIZE) { >> + for (; addr != end; pte += nr, addr += nr * PAGE_SIZE) { >> + max_nr = (end - addr) >> PAGE_SHIFT; >> + nr = 1; >> ptent = ptep_get(pte); >> if (pte_none(ptent)) >> continue; >> @@ -598,6 +602,10 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, >> folio = vm_normal_folio(vma, addr, ptent); >> if (!folio || folio_is_zone_device(folio)) >> continue; >> + if (folio_test_large(folio) && max_nr != 1) >> + nr = folio_pte_batch(folio, addr, pte, ptent, >> + max_nr, fpb_flags, >> + NULL, NULL, NULL); >> /* >> * vm_normal_folio() filters out zero pages, but there might >> * still be reserved folios to skip, perhaps in a VDSO. >> @@ -630,7 +638,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, >> if (!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) || >> !vma_migratable(vma) || >> !migrate_folio_add(folio, qp->pagelist, flags)) { >> - qp->nr_failed++; >> + qp->nr_failed += nr; > > Sorry for chiming in late, but I am not convinced that 'qp->nr_failed' > should add 'nr' when isolation fails. This patch does not change the existing behavior. But I stumbled over that as well ... and scratched my head. > > From the comments of queue_pages_range(): > " > * >0 - this number of misplaced folios could not be queued for moving > * (a hugetlbfs page or a transparent huge page being counted as 1). > " > > That means if a large folio is failed to isolate, we should only add '1' > for qp->nr_failed instead of the number of pages in this large folio. Right? I think what the doc really meant is "PMD-mapped THP". PTE-mapped THPs always had the same behavior: per PTE of the THP we would increment nr_failed by 1. I assume returning "1" for PMD-mapped THPs was wrong from the beginning; it might only have been right for hugetlb pages. With COW and similar things (VMA splits), achieving "count each folio only once" reliably is a very hard thing to achieve. Let's explore how "nr_failed" will get used. 1) do_mbind() Only cares if "any failed", not the exact number. 2) migrate_pages() Will return the number to user space, where documentation says: "On success migrate_pages() returns the number of pages that could not be moved (i.e., a return of zero means that all pages were successfully moved)." man-page does not document THP specifics AFAIKs. I would assume most users care about "all migrated vs. any not migrated". I would even feel confident to change the THP PMD-handling to return the actual *pages*. -- Cheers, David / dhildenb