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SubjectRe: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()
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On 10/04/2019 01:55 PM, David Hildenbrand wrote:
> On 03.10.19 14:14, Qian Cai wrote:
>>
>>
>>> On Oct 3, 2019, at 8:01 AM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote:
>>>
>>> Will something like this be better ?
>>
>> Not really. dump_page() will dump PageCompound information anyway, so it is trivial to figure out if went in that path.
>>
>
> I agree, I use the dump_page() output frequently to identify PG_reserved
> pages. No need to duplicate that.

Here in this path there is a reserved page which is preventing
offlining a memory section but unfortunately dump_page() does
not print page->flags for a reserved page pinned there possibly
through memblock_reserve() during boot.

__offline_pages()
start_isolate_page_range()
set_migratetype_isolate()
has_unmovable_pages()
dump_page()

[ 64.920970] ------------[ cut here ]------------
[ 64.921718] WARNING: CPU: 16 PID: 1116 at mm/page_alloc.c:8298 has_unmovable_pages+0x274/0x2a8
[ 64.923110] Modules linked in:
[ 64.923634] CPU: 16 PID: 1116 Comm: bash Not tainted 5.5.0-rc6-00006-gca544f2a11ae-dirty #281
[ 64.925102] Hardware name: linux,dummy-virt (DT)
[ 64.925905] pstate: 60400085 (nZCv daIf +PAN -UAO)
[ 64.926742] pc : has_unmovable_pages+0x274/0x2a8
[ 64.927554] lr : has_unmovable_pages+0x298/0x2a8
[ 64.928359] sp : ffff800014fd3a00
[ 64.928944] x29: ffff800014fd3a00 x28: fffffe0017640000
[ 64.929875] x27: 0000000000000000 x26: ffff0005fcfcda00
[ 64.930810] x25: 0000000000640000 x24: 0000000000000003
[ 64.931736] x23: 0000000019840000 x22: 0000000000001380
[ 64.932667] x21: ffff800011259000 x20: ffff0005fcfcda00
[ 64.933588] x19: 0000000000661000 x18: 0000000000000010
[ 64.934514] x17: 0000000000000000 x16: 0000000000000000
[ 64.935454] x15: ffffffffffffffff x14: ffff8000118498c8
[ 64.936377] x13: ffff800094fd3797 x12: ffff800014fd379f
[ 64.937304] x11: ffff800011861000 x10: ffff800014fd3720
[ 64.938226] x9 : 00000000ffffffd0 x8 : ffff8000106a60d0
[ 64.939156] x7 : 0000000000000000 x6 : ffff0005fc6261b0
[ 64.940078] x5 : ffff0005fc6261b0 x4 : 0000000000000000
[ 64.941003] x3 : ffff0005fc62cf80 x2 : ffffffffffffec80
[ 64.941927] x1 : ffff800011141b58 x0 : ffff0005fcfcda00
[ 64.942857] Call trace:
[ 64.943298] has_unmovable_pages+0x274/0x2a8
[ 64.944056] start_isolate_page_range+0x258/0x360
[ 64.944879] __offline_pages+0xf4/0x9e8
[ 64.945554] offline_pages+0x10/0x18
[ 64.946189] memory_block_action+0x40/0x1a0
[ 64.946929] memory_subsys_offline+0x4c/0x78
[ 64.947679] device_offline+0x98/0xc8
[ 64.948328] unprobe_store+0xa8/0x158
[ 64.948976] dev_attr_store+0x14/0x28
[ 64.949628] sysfs_kf_write+0x40/0x50
[ 64.950273] kernfs_fop_write+0x108/0x218
[ 64.950983] __vfs_write+0x18/0x40
[ 64.951592] vfs_write+0xb0/0x1d0
[ 64.952175] ksys_write+0x64/0xe8
[ 64.952761] __arm64_sys_write+0x18/0x20
[ 64.953451] el0_svc_common.constprop.2+0x88/0x150
[ 64.954293] el0_svc_handler+0x20/0x80
[ 64.954963] el0_sync_handler+0x118/0x188
[ 64.955669] el0_sync+0x140/0x180
[ 64.956256] ---[ end trace b162b4d1cbea304d ]---
[ 64.957063] page:fffffe0017640000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
[ 64.958489] raw: 1ffff80000001000 fffffe0017640008 fffffe0017640008 0000000000000000
[ 64.959839] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[ 64.961174] page dumped because: unmovable page

The reason is dump_page() does not print page->flags universally
and only does so for KSM, Anon and File pages while excluding
reserved pages at boot. Wondering should not we make printing
page->flags universal ?

- Anshuman

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