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b=oqQdBh9sl6T/WoQmTaqwSb+Hf0W7EvI/kz5P31jLzegkKDtz2Ljid8W0a6qZvnbdH eh1iE41dYG47VNOpmCQZCYvp9S0EbWv4zIhmPQGuuYHEqA57hGvaJycE2ykfOHa4iW raj3idE2OVz3b6S7FnTiM+vfW54nZvXs0fAMPWFmZjQAJEr2z0EEGBo/L7rM1W/dgD oAexAibCpB0/ZsKxrnQW2VWR9Kz8Y2pDd2ehZjP5DQqbDefH+p0w73/85XuGLf1mET htAEXO7MRYF67M6LBaqMqGw9PkiMXaG3vxVURvUTUzoTe6JqMIrNZCenwDS9evvaYZ N3C0d6yewvc7g== Message-ID: Date: Sat, 7 Feb 2026 22:38:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v7 4/5] mm: khugepaged: skip lazy-free folios To: Lance Yang , Barry Song <21cnbao@gmail.com>, Vernon Yang Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260207081613.588598-1-vernon2gm@gmail.com> <20260207081613.588598-5-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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: bwhocwkcwboyde7dgfbto8w68eunob5q X-Rspamd-Queue-Id: D93D78000E X-Rspam-User: X-HE-Tag: 1770500314-766310 X-HE-Meta: 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 DP1wtCyG RX525JyV2vtS48HrKtFa3XH7SceYdJN5w0jFsWAlQpkT3/ZHXBQKi5uZATzSvKOCesV2U/v18V+nPgkGt2wNjcFXg9M4bnYB9IlflAaIDV10N/dAfoujrcagPEvB8LrOOrJpWV4AiS5/Y5sEuo8YMDXhWFqXILfGt75gYymlPB6uskJY7pxn8V5UyoGfFG4Krc4ek8OX0veZo2Tlz5hw1jZTOTZdxlxp6PN9NlLYHaoctUlmQjNndR1cXcs2cQoElO398QlLvnheJ5Oh2wFtrEbLNf1i2Gh33BK3yfoEaPnyIWbAbxiZklEu0n66xlA5W1K/UqGY7+krz/C0= 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 2/7/26 14:51, Lance Yang wrote: > > > On 2026/2/7 16:34, Barry Song wrote: >> On Sat, Feb 7, 2026 at 4:16 PM 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 and then 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 >>> Acked-by: David Hildenbrand (arm) >>> Reviewed-by: Lance 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 8b68ae3bc2c5..0d160e612e16 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)) { >> >> We have two corner cases here: > > Good catch! > >> >> 1. Even if a lazyfree folio is dirty, if the VMA has the VM_DROPPABLE >> flag, >> a lazyfree folio may still be dropped, even when its PTE is dirty. Good point! > > Right. When the VMA has VM_DROPPABLE, we would drop the lazyfree folio > regardless of whether it (or the PTE) is dirty in try_to_unmap_one(). > > So, IMHO, we could go with: > > cc->is_khugepaged && folio_test_lazyfree(folio) && >     (!pte_dirty(pteval) || (vma->vm_flags & VM_DROPPABLE)) Hm. In a VM_DROPPABLE mapping all folios should be marked as lazy-free (see folio_add_new_anon_rmap()). The new (collapse) folio will also be marked lazy (due to folio_add_new_anon_rmap()) free and can just get dropped any time. So likely we should just not skip collapse for lazyfree folios in VM_DROPPABLE mappings? if (cc->is_khugepaged && !(vma->vm_flags & VM_DROPPABLE) && folio_test_lazyfree(folio) && !pte_dirty(pteval)) { ... } -- Cheers, David