Re: [PATCH] mm: Disable deferred struct page for 32-bit arches

[Michal Hocko <mhocko@kernel.org>]

On Fri 31-08-18 15:05:09, Pavel Tatashin wrote:
> Deferred struct page init is needed only on systems with large amount of
> physical memory to improve boot performance. 32-bit systems do not benefit
> from this feature.
> 
> Jiri reported a problem where deferred struct pages do not work well with
> x86-32:
> 
> [    0.035162] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
> [    0.035725] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
> [    0.036269] Initializing CPU#0
> [    0.036513] Initializing HighMem for node 0 (00036ffe:0007ffe0)
> [    0.038459] page:f6780000 is uninitialized and poisoned
> [    0.038460] raw: ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
> [    0.039509] page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
> [    0.040038] ------------[ cut here ]------------
> [    0.040399] kernel BUG at include/linux/page-flags.h:293!
> [    0.040823] invalid opcode: 0000 [#1] SMP PTI
> [    0.041166] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc1_pt_jiri #9
> [    0.041694] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014
> [    0.042496] EIP: free_highmem_page+0x64/0x80
> [    0.042839] Code: 13 46 d8 c1 e8 18 5d 83 e0 03 8d 04 c0 c1 e0 06 ff 80 ec 5f 44 d8 c3 8d b4 26 00 00 00 00 ba 08 65 28 d8 89 d8 e8 fc 71 02 00 <0f> 0b 8d 76 00 8d bc 27 00 00 00 00 ba d0 b1 26 d8 89 d8 e8 e4 71
> [    0.044338] EAX: 0000003c EBX: f6780000 ECX: 00000000 EDX: d856cbe8
> [    0.044868] ESI: 0007ffe0 EDI: d838df20 EBP: d838df00 ESP: d838defc
> [    0.045372] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00210086
> [    0.045913] CR0: 80050033 CR2: 00000000 CR3: 18556000 CR4: 00040690
> [    0.046413] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> [    0.046913] DR6: fffe0ff0 DR7: 00000400
> [    0.047220] Call Trace:
> [    0.047419]  add_highpages_with_active_regions+0xbd/0x10d
> [    0.047854]  set_highmem_pages_init+0x5b/0x71
> [    0.048202]  mem_init+0x2b/0x1e8
> [    0.048460]  start_kernel+0x1d2/0x425
> [    0.048757]  i386_start_kernel+0x93/0x97
> [    0.049073]  startup_32_smp+0x164/0x168
> [    0.049379] Modules linked in:
> [    0.049626] ---[ end trace 337949378db0abbb ]---
> 
> We free highmem pages before their struct pages are initialized:
> 
> mem_init()
>  set_highmem_pages_init()
>   add_highpages_with_active_regions()
>    free_highmem_page()
>     .. Access uninitialized struct page here..
> 
> Because there is no reason to have this feature on 32-bit systems, just
> disable it.
> 
> Fixes: 2e3ca40f03bb ("mm: relax deferred struct page requirements")
> Cc: stable@vger.kernel.org
> 
> Reported-by: Jiri Slaby <jslaby@suse.cz>
> Signed-off-by: Pavel Tatashin <pavel.tatashin@microsoft.com>

I would swear something like this has been already proposed.
Anyway, looks good to me. I guess we could fix 32b but there is no good
reason to complicate 32b code just to allow for an optimization which is
not worth it.

Acked-by: Michal Hocko <mhocko@suse.com>
> ---
>  mm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index a550635ea5c3..de64ea658716 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -637,6 +637,7 @@ config DEFERRED_STRUCT_PAGE_INIT
>  	depends on NO_BOOTMEM
>  	depends on SPARSEMEM
>  	depends on !NEED_PER_CPU_KM
> +	depends on 64BIT
>  	help
>  	  Ordinarily all struct pages are initialised during early boot in a
>  	  single thread. On very large machines this can take a considerable
> -- 
> 2.18.0

-- 
Michal Hocko
SUSE Labs