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b=MU/N+J+fpUR5yRHF7vZJwWV1SL9ejrPGZHTnhoITcVf6+Efy3EQJexo8qZ51aBwHk 6xnHXayzDnSp4PN0CwVLWHtcMvTR9ifTWXmk0SaFkjgCi+MTncPwfXQ7n79gRAqzU8 GAeRLTFFUca00AwoTo4Gauy6iuFZV16YqUB7iPw2RKuIdZxiNCOz4YD/5Y+f4wfMc1 B57jgPu69YzAas+jCOpEFY1kCyhf/faENxiQ/pfdNgJJxrS1XMzCSUQa8AlDPJeRKi ABGa3iEQ+LjhmCK/pHgLQF8LgVFoqcuL3vOxRpaprxxUh+36HW4C1z+55oDdiDr1uM caJ4/5l1+ihlQ== Message-ID: Date: Tue, 7 Apr 2026 17:00:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: ksm: add mremap selftests for ksm_rmap_walk To: xu.xin16@zte.com.cn, hughd@google.com, akpm@linux-foundation.org Cc: michel@lespinasse.org, ljs@kernel.org, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260407140805858ViqJKFhfmYSfq0FynsaEY@zte.com.cn> 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: <20260407140805858ViqJKFhfmYSfq0FynsaEY@zte.com.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: AAD05C000C X-Stat-Signature: chhmscpeugybi95ufcut7mmq9e97fzpu X-Rspam-User: X-HE-Tag: 1775574009-482734 X-HE-Meta: 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 HlmS9efq JJnjzM+SDtZijM2p4RkDD+CbLgL0+Jb62TdZwxylmPir3MgKx8bXkOKogFb0kLrodQbvN0EqAjyrPWjHPqOKzp4UqQqHWuR+9ig07PXo8gxTBsSB82tne0H/dJzACWNn3LGsYZCgF3h3LzdCcwsGwrV9yRgaR/P1qqbsF+4Y7ihcD3Cay7urt25kFvs8Bd8iegLlaczojX4lS9wBt0uoCgIbvIpeYMNwP/9BAUE7XIaHQefm2/MKntyYDsVQS7zIi0RmHbSoWlbF/IyU58qKgC+I74sNQ2RyI+WOf5bUG71RjwTucYkam4kLi3mka7tQG5fd18MhQMoLr3fWlxEAQBRQpPES++VKOQO6mqxCAOORQxFngxiHdUY5trYjrpsztiQLU Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/7/26 08:08, xu.xin16@zte.com.cn wrote: > From: xu xin > > The existing tools/testing/selftests/mm/rmap.c has already one testcase > for ksm_rmap_walk in TEST_F(migrate, ksm), which takes use of migration > of page from one NUMA node to another NUMA node. However, it just lacks > the senario of mremapped VMAs. > > Before migrating, we add the calling of mremap() to address mapped with KSM > pages, which is specailly to test a optimization which is introduced by this > patch ("ksm: Optimize rmap_walk_ksm by passing a suitable address range") > https://lore.kernel.org/all/20260212193045556CbzCX8p9gDu73tQ2nvHEI@zte.com.cn/ > > Result: > TAP version 13 > 1..5 > ok 1 migrate.anon > ok 2 migrate.shm > ok 3 migrate.file # SKIP Failed in worker > ok 4 migrate.ksm > ok 5 migrate.ksm_and_mremap > > Signed-off-by: xu xin > --- > tools/testing/selftests/mm/rmap.c | 69 ++++++++++++++++++++++++++++ > tools/testing/selftests/mm/vm_util.c | 38 +++++++++++++++ > tools/testing/selftests/mm/vm_util.h | 2 + > 3 files changed, 109 insertions(+) > > diff --git a/tools/testing/selftests/mm/rmap.c b/tools/testing/selftests/mm/rmap.c > index 53f2058b0ef2..65470def2bf1 100644 > --- a/tools/testing/selftests/mm/rmap.c > +++ b/tools/testing/selftests/mm/rmap.c > @@ -430,4 +430,73 @@ TEST_F(migrate, ksm) > propagate_children(_metadata, data); > } > > +/* To test if ksm page can be migrated when it's mremapped */ > +int merge_mremap_and_migrate(struct global_data *data) > +{ > + int ret = 0; > + /* Allocate range and set the same data */ > + data->mapsize = 3*getpagesize(); > + data->region = mmap(NULL, data->mapsize, PROT_READ|PROT_WRITE, > + MAP_PRIVATE|MAP_ANON, -1, 0); > + if (data->region == MAP_FAILED) > + ksft_exit_fail_perror("mmap failed"); > + > + memset(data->region, 0x77, data->mapsize); What happens if you mremap() after faulting, but before merging? rmap_item->address always holds the user space address of the entry in the parent process. It must match the one in the child process, because mremap() will unmerge/unshare in the child. And it must match the one in the parent, as mremap() would similarly unmerge/unshare. Maybe doing the mremap() before merging (but after faulting) would trigger what Hugh described. break_cow() and friends don't care about the rmap, as they simply jump directly to the user space address in the process. In rmap_walk_ksm(), I think the concern Hugh raised is that we are using const pgoff_t pgoff = rmap_item->address >> PAGE_SHIFT; but we'd actually need a pgoff into the anon_vma. Without mremap, it does not matter, they are the same (tests keep passing). But with mremap it's not longer the same. I think one could store it in the ksm_rmap_item, but that would increase it's size. It's essentially the folio->index of the original page we are replacing. Or we could just remember "pgoff is not that simple because mremap was involved, so walk the whole damn thing". We could also just try walking all involved processes, looking only at that user space address (but that gets more tricky with rmap locking etc ...). Anyhow, I think that's the concern Hugh raised, IIUC. > + > + if (ksm_start() < 0) > + return FAIL_ON_CHECK; > + > + /* 1 2 expected */ > + ksft_print_msg("Shared: %ld (1 expected) Sharing: %ld (2 expected)\n", > + ksm_get_pages_shared(), ksm_get_pages_sharing()); > + > + /* > + * Mremap the second pagesize address range into the third pagesize > + * address. > + */ > + data->region = mremap(data->region + getpagesize(), getpagesize(), getpagesize(), > + MREMAP_MAYMOVE|MREMAP_FIXED, data->region + 2*getpagesize()); There would not be a KSM page after this mremap(), no? -- Cheers, David