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(p200300d82f23c700d8ae41bf492a9e4c.dip0.t-ipconnect.de. [2003:d8:2f23:c700:d8ae:41bf:492a:9e4c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3bb656dbec5sm4669828f8f.31.2025.08.16.00.22.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 16 Aug 2025 00:22:31 -0700 (PDT) Message-ID: Date: Sat, 16 Aug 2025 09:22:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m To: Huacai Chen , Huacai Chen , Andrew Morton Cc: linux-mm@kvack.org, Zi Yan , Lorenzo Stoakes , Harry Yoo , linux-kernel@vger.kernel.org, Minchan Kim , Sergey Senozhatsky , "Michael S. Tsirkin" References: <20250815090539.1578484-1-chenhuacai@loongson.cn> From: David Hildenbrand Content-Language: en-US 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: <20250815090539.1578484-1-chenhuacai@loongson.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.08.25 11:05, Huacai Chen wrote: Hi, please CC the appropriate maintainers next time. You missed (some) balloon and zsmalloc maintainers. > After commit 84caf98838a3e5f4bdb34 ("mm: stop storing migration_ops in > page->mapping") we get such an error message if CONFIG_ZSMALLOC=m: > > WARNING: CPU: 3 PID: 42 at mm/migrate.c:142 isolate_movable_ops_page+0xa8/0x1c0 > CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT > pc 9000000000540bd8 ra 9000000000540b84 tp 9000000100420000 sp 9000000100423a60 > a0 9000000100193a80 a1 000000000000000c a2 000000000000001b a3 ffffffffffffffff > a4 ffffffffffffffff a5 0000000000000267 a6 0000000000000000 a7 9000000100423ae0 > t0 00000000000000f1 t1 00000000000000f6 t2 0000000000000000 t3 0000000000000001 > t4 ffffff00010eb834 t5 0000000000000040 t6 900000010c89d380 t7 90000000023fcc70 > t8 0000000000000018 u0 0000000000000000 s9 ffffff00010eb800 s0 ffffff00010eb800 > s1 000000000000000c s2 0000000000043ae0 s3 0000800000000000 s4 900000000219cc40 > s5 0000000000000000 s6 ffffff00010eb800 s7 0000000000000001 s8 90000000025b4000 > ra: 9000000000540b84 isolate_movable_ops_page+0x54/0x1c0 > ERA: 9000000000540bd8 isolate_movable_ops_page+0xa8/0x1c0 > CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE) > PRMD: 00000004 (PPLV0 +PIE -PWE) > EUEN: 00000000 (-FPE -SXE -ASXE -BTE) > ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7) > ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0) > PRID: 0014c010 (Loongson-64bit, Loongson-3A5000) > CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT > Stack : 90000000021fd000 0000000000000000 9000000000247720 9000000100420000 > 90000001004236a0 90000001004236a8 0000000000000000 90000001004237e8 > 90000001004237e0 90000001004237e0 9000000100423550 0000000000000001 > 0000000000000001 90000001004236a8 725a84864a19e2d9 90000000023fcc58 > 9000000100420000 90000000024c6848 9000000002416848 0000000000000001 > 0000000000000000 000000000000000a 0000000007fe0000 ffffff00010eb800 > 0000000000000000 90000000021fd000 0000000000000000 900000000205cf30 > 000000000000008e 0000000000000009 ffffff00010eb800 0000000000000001 > 90000000025b4000 0000000000000000 900000000024773c 00007ffff103d748 > 00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d > ... > Call Trace: > [<900000000024773c>] show_stack+0x5c/0x190 > [<90000000002415e0>] dump_stack_lvl+0x70/0x9c > [<90000000004abe6c>] isolate_migratepages_block+0x3bc/0x16e0 > [<90000000004af408>] compact_zone+0x558/0x1000 > [<90000000004b0068>] compact_node+0xa8/0x1e0 > [<90000000004b0aa4>] kcompactd+0x394/0x410 > [<90000000002b3c98>] kthread+0x128/0x140 > [<9000000001779148>] ret_from_kernel_thread+0x28/0xc0 > [<9000000000245528>] ret_from_kernel_thread_asm+0x10/0x88 > > The reason is that defined(CONFIG_ZSMALLOC) evaluates to 1 only when > CONFIG_ZSMALLOC=y, we should use IS_ENABLED(CONFIG_ZSMALLOC) instead. Ouch, I missed that CONFIG_ZSMALLOC can be configured like that. I thought it would always be builtin. > But when I use IS_ENABLED(CONFIG_ZSMALLOC), page_movable_ops() cannot > access zsmalloc_mops because zsmalloc_mops is in a module. > > To solve this problem, we define a movable_ops[] array in mm/migrate.c, > initialise its elements at mm/balloon_compaction.c & mm/zsmalloc.c, and > let the page_movable_ops() function return elements from movable_ops[]. Before I took that easy route to just get it working quickly, I envisioned a proper registration interface. See below. > > Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping") > Signed-off-by: Huacai Chen > --- > include/linux/migrate.h | 6 ++++++ > mm/balloon_compaction.c | 7 +++++++ > mm/migrate.c | 16 ++++++++++------ > mm/zsmalloc.c | 6 ++++++ > 4 files changed, 29 insertions(+), 6 deletions(-) > > diff --git a/include/linux/migrate.h b/include/linux/migrate.h > index acadd41e0b5c..58fac171e4d5 100644 > --- a/include/linux/migrate.h > +++ b/include/linux/migrate.h > @@ -57,6 +57,12 @@ struct movable_operations { > void (*putback_page)(struct page *); > }; > > +#define MOVABLE_BALLOON 0 > +#define MOVABLE_ZSMALLOC 1 > +#define MOVABLE_MAX 2 > + > +extern const struct movable_operations *movable_ops[MOVABLE_MAX]; > + > /* Defined in mm/debug.c: */ > extern const char *migrate_reason_names[MR_TYPES]; > > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > index 2a4a649805c1..a1d2625b5c39 100644 > --- a/mm/balloon_compaction.c > +++ b/mm/balloon_compaction.c > @@ -254,4 +254,11 @@ const struct movable_operations balloon_mops = { > .putback_page = balloon_page_putback, > }; > > +static int __init balloon_init(void) > +{ > + movable_ops[MOVABLE_BALLOON] = &balloon_mops; > + return 0; > +} > +core_initcall(balloon_init); > + > #endif /* CONFIG_BALLOON_COMPACTION */ > diff --git a/mm/migrate.c b/mm/migrate.c > index 425401b2d4e1..92918fab3e1a 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -53,6 +53,10 @@ > #include "internal.h" > #include "swap.h" > > +const struct movable_operations *movable_ops[MOVABLE_MAX]; > + > +EXPORT_SYMBOL(movable_ops); > + > static const struct movable_operations *page_movable_ops(struct page *page) > { > VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page); > @@ -62,15 +66,15 @@ static const struct movable_operations *page_movable_ops(struct page *page) > * it as movable, the page type must be sticky until the page gets freed > * back to the buddy. > */ > -#ifdef CONFIG_BALLOON_COMPACTION > +#if IS_ENABLED(CONFIG_BALLOON_COMPACTION) > if (PageOffline(page)) > /* Only balloon compaction sets PageOffline pages movable. */ > - return &balloon_mops; > -#endif /* CONFIG_BALLOON_COMPACTION */ > -#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) > + return movable_ops[MOVABLE_BALLOON]; > +#endif /* IS_ENABLED(CONFIG_BALLOON_COMPACTION) */ > +#if IS_ENABLED(CONFIG_ZSMALLOC) && IS_ENABLED(CONFIG_COMPACTION) > if (PageZsmalloc(page)) > - return &zsmalloc_mops; > -#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */ > + return movable_ops[MOVABLE_ZSMALLOC]; > +#endif /* IS_ENABLED(CONFIG_ZSMALLOC) && IS_ENABLED(CONFIG_COMPACTION) */ > return NULL; > } > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 2c5e56a65354..052fcc0d29e5 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -2246,6 +2246,9 @@ EXPORT_SYMBOL_GPL(zs_destroy_pool); > > static int __init zs_init(void) > { > +#ifdef CONFIG_MIGRATION > + movable_ops[MOVABLE_ZSMALLOC] = &zsmalloc_mops; > +#endif No, not like this. Please add a proper registration function, and use the page type as an input. int register_movable_ops(const struct movable_operations *, enum pagetype); Probably best to refuse any page_type except PGTY_offline and PGTY_zsmalloc for now, and let the function fail with -EBUSY if already registered. The function can have a stub that returns 0 without CONFIG_MIGRATION. The you can do here int rc; if (IS_ENABLED(CONFIG_MIGRATION)) { rc = register_movable_ops(&zsmalloc_mops, PGTY_zsmalloc); if (WARN_ON_ONCE(rc)) return rc; } -- Cheers David / dhildenb