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b=TB/gBxn0vfFQQb9YORjszU1lX5IkTjOJ1u3/7THf65vM0u8ZNr0FV57VeiWMStM/y 2YtN6AkLRFjRjW/c+r6hgkgX2JroCZ0CdqdKUjjql+ffDFpo40G8TIwxBIGzFtI60W 7szzPIuh3l/Bdd/mAtprfk8Q2UXb92+6iAs9OLVUg9wGmMTWnmmi/TZWZooZsLcOa7 OyNIpwTRUbbKYMoxw3mF2UjMymhO99IJ3Bok++/fR9erkdPjTTOXhXUAp7y0ix1Mcp OSaiXvkODeedQKWUcj3A1jg8AmfU+PCAnYrGGHSSdAi0AMMl6mLgvpaIPWkFly2MNh xT557Xa8tKrCQ== Message-ID: Date: Wed, 4 Feb 2026 22:23:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v6 4/5] mm: khugepaged: skip lazy-free folios To: Vernon Yang , akpm@linux-foundation.org Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260201122554.1470071-1-vernon2gm@gmail.com> <20260201122554.1470071-5-vernon2gm@gmail.com> From: "David Hildenbrand (arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260201122554.1470071-5-vernon2gm@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B7933140003 X-Stat-Signature: bo5x4suf8pxx5adu6ihq7p769adqa1ss X-Rspam-User: X-HE-Tag: 1770240241-14842 X-HE-Meta: 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 WYK6cI+2 dYzWXQ1g750rAVHskiLP2Ofd/9NgbnVAiesFHf5ba5X75szALnQsPQXLJ//47KieKk1JfzIHTXFTL1pdOSYB0dT9f/4fOVgQHUvDtsy43ADHcznPCaTI7yumY7NL4p4+kyGFsvFLIOGqCWhIZkLx8vCTgkixXKFwZDzTO+BUDIeiPYj6sTUiCH3XPBCM1B3ECNJoyTIUFaxp4ic0lRf9/+8p46bxecO0ZZMaVQ1sn5y/UgVkOgRgvm57dZSczVcN9Jb+MWIGBknbPV5LDa7MTyBGdSQ== 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 2/1/26 13:25, Vernon Yang wrote: > From: Vernon Yang > > For example, create three task: hot1 -> cold -> hot2. After all three > task are created, each allocate memory 128MB. the hot1/hot2 task > continuously access 128 MB memory, while the cold task only accesses > its memory briefly andthen call madvise(MADV_FREE). However, khugepaged > still prioritizes scanning the cold task and only scans the hot2 task > after completing the scan of the cold task. > > And if we collapse with a lazyfree page, that content will never be none > and the deferred shrinker cannot reclaim them. > > So if the user has explicitly informed us via MADV_FREE that this memory > will be freed, it is appropriate for khugepaged to skip it only, thereby > avoiding unnecessary scan and collapse operations to reducing CPU > wastage. > > Here are the performance test results: > (Throughput bigger is better, other smaller is better) > > Testing on x86_64 machine: > > | task hot2 | without patch | with patch | delta | > |---------------------|---------------|---------------|---------| > | total accesses time | 3.14 sec | 2.93 sec | -6.69% | > | cycles per access | 4.96 | 2.21 | -55.44% | > | Throughput | 104.38 M/sec | 111.89 M/sec | +7.19% | > | dTLB-load-misses | 284814532 | 69597236 | -75.56% | > > Testing on qemu-system-x86_64 -enable-kvm: > > | task hot2 | without patch | with patch | delta | > |---------------------|---------------|---------------|---------| > | total accesses time | 3.35 sec | 2.96 sec | -11.64% | > | cycles per access | 7.29 | 2.07 | -71.60% | > | Throughput | 97.67 M/sec | 110.77 M/sec | +13.41% | > | dTLB-load-misses | 241600871 | 3216108 | -98.67% | > > Signed-off-by: Vernon Yang > --- > include/trace/events/huge_memory.h | 1 + > mm/khugepaged.c | 13 +++++++++++++ > 2 files changed, 14 insertions(+) > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 384e29f6bef0..bcdc57eea270 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -25,6 +25,7 @@ > EM( SCAN_PAGE_LRU, "page_not_in_lru") \ > EM( SCAN_PAGE_LOCK, "page_locked") \ > EM( SCAN_PAGE_ANON, "page_not_anon") \ > + EM( SCAN_PAGE_LAZYFREE, "page_lazyfree") \ > EM( SCAN_PAGE_COMPOUND, "page_compound") \ > EM( SCAN_ANY_PROCESS, "no_process_for_page") \ > EM( SCAN_VMA_NULL, "vma_null") \ > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index df22b2274d92..b4def001ccd0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -46,6 +46,7 @@ enum scan_result { > SCAN_PAGE_LRU, > SCAN_PAGE_LOCK, > SCAN_PAGE_ANON, > + SCAN_PAGE_LAZYFREE, > SCAN_PAGE_COMPOUND, > SCAN_ANY_PROCESS, > SCAN_VMA_NULL, > @@ -583,6 +584,12 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, > folio = page_folio(page); > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > + if (cc->is_khugepaged && !pte_dirty(pteval) && > + folio_test_lazyfree(folio)) { Should be aligned as if (cc->is_khugepaged && !pte_dirty(pteval) && folio_test_lazyfree(folio)) { But you could just have it in a single line. > + result = SCAN_PAGE_LAZYFREE; > + goto out; > + } > + > /* See hpage_collapse_scan_pmd(). */ > if (folio_maybe_mapped_shared(folio)) { > ++shared; > @@ -1332,6 +1339,12 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, > } > folio = page_folio(page); > > + if (cc->is_khugepaged && !pte_dirty(pteval) && > + folio_test_lazyfree(folio)) { > + result = SCAN_PAGE_LAZYFREE; > + goto out_unmap; > + } Dito. > + > if (!folio_test_anon(folio)) { > result = SCAN_PAGE_ANON; > goto out_unmap; Surprised that there is no need to add checks for SCAN_PAGE_LAZYFREE anywhere, but it's similar to SCAN_PAGE_LOCK just that we cannot ever run into it for madvise. Acked-by: David Hildenbrand (arm) -- Cheers, David