linux-kernel - Re: [PATCH V4] mm/migrate: Fix NULL movable_ops if CONFIG

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Message-ID: <7a10a5bf-95d9-463c-bbea-50f96920ee73@redhat.com>
Date: Sun, 17 Aug 2025 19:34:53 +0200
From: David Hildenbrand <david@...hat.com>
To: Huacai Chen <chenhuacai@...ngson.cn>, Huacai Chen
 <chenhuacai@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, Zi Yan <ziy@...dia.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Harry Yoo <harry.yoo@...cle.com>, Minchan Kim <minchan@...nel.org>,
 Sergey Senozhatsky <senozhatsky@...omium.org>,
 "Michael S . Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

On 17.08.25 17:17, Huacai Chen wrote:
> 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.
> 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 set_movable_ops() interface to
> register and unregister offline_movable_ops / zsmalloc_movable_ops in
> mm/migrate.c, and call them at mm/balloon_compaction.c & mm/zsmalloc.c.
> Since offline_movable_ops / zsmalloc_movable_ops are always accessible,
> all #ifdef / #endif are removed in page_movable_ops().
> 
> Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping")
> Acked-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---

Thanks!

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb