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b=humF71ebabeqOf720kG9Kp3v1uYNN24B/eb+zf0MwE0EGHGt2SYsVKdjAeLFIYQPE JpKTQti9qdA1UD0aJ2wjmmtixB9bFuBuNiNW0fwF3ilqHrSx2t8VLzRyRIbw6bmN2c saJYL9J6ElfuXkNpR6MQZlw5JCLTibOual5FmZzEu5pm/AbinbE1hM/XAFIdXV+6lp ry3tOJfVitrM3Lyzuapcby8OwKWlDVY+ikszsrQmDUWK8FIDdhxWVxq5Q8e1n+TcQb aqgJswJUKR+MLwPFaGtVmpizs2Uk+dbXHjxKIPqVsgEKItt6A0x3cOseQpYN4SmQs0 PcSyJjFVX2qNQ== Message-ID: Date: Wed, 1 Apr 2026 09:32:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 0/2] Fix storing in XArray check_split tests To: Zi Yan Cc: Ackerley Tng , willy@infradead.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, michael.roth@amd.com, dev.jain@arm.com, vannapurve@google.com References: <6ada27e1-8f85-4b85-8c25-bc9207b2624d@kernel.org> <87FD20AF-55B6-4129-9AED-E2E854593883@nvidia.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: <87FD20AF-55B6-4129-9AED-E2E854593883@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 437D014000A X-Stat-Signature: kmzbfc5ahynbw3xe91kui1x9zbh1j1x4 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775028757-476251 X-HE-Meta: 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 rzwPtAeW 8VXmB2rL8tKZ4IgoaJr0q8fjWhyS8nP66HX6ERFwE6ztWP755uR3ZoVvlVbFvywr6y24yOyEA6d17WO2R4J74Ci7wjYUunfGjHd0jBJbOJF6Pzh06d7yBqxFtmgzjsAfQJ2l/+G/lPUb7tpdtRLynVa/bfwldkOuSROrJZsUk1VPwjEv3CMYHThpvVpjITxRyZvNkUnHG5D8YUZCY8DUW2Fnmp89FMEsG8Pfjve27K2hZV1PJmStKTFE1HS1PzuL6HqnAU7rguTvSmqdGMlEAwAXAPvkHIVdr08QopomAuFprVFXRZNi5QfKD+A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/16/26 17:49, Zi Yan wrote: > On 16 Mar 2026, at 12:23, David Hildenbrand (Arm) wrote: > >> On 2/23/26 08:34, Ackerley Tng wrote: >>> Hi, >>> >>> I hit an assertion while making some modifications to >>> lib/test_xarray.c [1] and I believe this is the fix. >>> >>> In check_split, the tests split the XArray node and then store values >>> after the split to verify that splitting worked. While storing and >>> retrieval works as expected, the node's metadata, specifically >>> node->nr_values, is not updated correctly. >>> >>> This led to the assertion being hit in [1], since the storing process >>> did not increment node->nr_values sufficiently, while the erasing >>> process assumed the fully-incremented node->nr_values state. >>> >>> Would like to check my understanding on these: >>> >>> 1. In the multi-index xarray world, is node->nr_values definitely the >>> total number of values *and siblings* in the node? >>> >>> 2. IIUC xas_store() has significantly different behavior when entry is >>> NULL vs non-NULL: when entry is NULL, xas_store() does not make >>> assumptions on the number of siblings and erases all the way till >>> the next non-sibling entry. This sounds fair to me, but it's also >>> kind of surprising that it is differently handled when entry is >>> non-NULL, where xas_store() respects xas->xa_sibs. >>> >>> 3. If xas_store() is dependent on its caller to set up xas correctly >>> (also sounds fair), then there are places where xas_store() is >>> used, like replace_page_cache_folio() or >>> migrate_huge_page_move_mapping(), where xas is set up assuming 0 >>> order pages. Are those buggy? >> >> Zi, do you have any familiarity with that code and could help? > > Not much. But I used lib/test_xarray.c to did a test: > > 1. initialize an xarray with order 6 and set entry to 0, > > 2. add a new xas like XA_STATE(xas0, xa, 0); > 3. xas_store(&xas0, xa_mk_value(32)); > > 4. add a new xas like XA_STATE(xas0, xa, 16); > 5. xas_store(&xas0, xa_mk_value(48)); > > The outcome is that xas_store() does not change xarray structure, > namely the orders are preserved. No issue is present. > > After 2 and 3, the xarray is still order 6, but its 0-63 entries (all order-6) > are changed from 0 to 32. > After 4 and 5, the xarray is still order 6, but its 0-63 entries > are changed from 32 to 48. > > I will need to dig into the code more to explain how xas_store() works. Zi, we discussed this topic with Willy in the THP cabal call. I did not get all the details, do you remember our conclusion? (I can try getting access to the recording) -- Cheers, David