About SECTION_SIZE_BITS for Sparsemem

Mon Jul 12 05:35:39 EDT 2010

Interesting.

I got tested with
#define MAX_PHYSMEM_BITS        31
#define SECTION_SIZE_BITS       27

# cat /proc/sys/vm/min_free_kbytes
1832
# echo 1828 > /proc/sys/vm/min_free_kbytes
# cat /proc/sys/vm/min_free_kbytes
1828
# echo 1820 > /proc/sys/vm/min_free_kbytes
# cat /proc/sys/vm/min_free_kbytes
1820
# echo 1700 > /proc/sys/vm/min_free_kbytes
# cat /proc/sys/vm/min_free_kbytes
1700

No kernel panic.

Thank you,
Kyungmin Park

On Mon, Jul 12, 2010 at 5:32 PM, Kukjin Kim <kgene.kim at samsung.com> wrote:
> Russell,
>
> Hi,
>
> Kukjin Kim wrote:
>> Russell wrote:
>> > So, memory starts at 0x20000000 and finishes at 0x25000000.  That's
> fine.
>> > That doesn't mean the section size is 16MB.
>> >
>> > As I've already said, the section size has _nothing_ what so ever to do
>> > with the size of memory, or the granularity of the size of memory.  By
>> > way of illustration, it is perfectly legal to have a section size of
>> > 256MB but only have 1MB in a section and this is perfectly legal.  So
>> > sections do not have to be completely filled.
>> >
>> Actually, as you know, the hole's area of mem_map is freed from bootmem if
> a
>> section has a hole when initializing sparse memory.
>>
>> I identified that a section doesn't need to be a contiguous area of
> physical
>> memory when reading your comment with the fact that the mem_map of a
> section
>> can be smaller than the size of a section.
>>
>> I found, however, the kernel panics when modifying min_free_kbytes file in
>> the proc filesystem if a section has a hole.
>>
>> While processing the change of min_free_kbytes in the kernel, page
>> descriptors in a hole of an online section is accessed.
>
> As I said, following error happens.
> It would be helpful to me if any opinions or comments.
>
> ---
> When SECTION_SIZE_BITS is 24 (16MiB),
>
> [root at Samsung ~]# cat /proc/sys/vm/min_free_kbytes
> 2736
> [root at Samsung ~]# echo "2730" > /proc/sys/vm/min_free_kbytes
>
> [root at Samsung ~]# cat /proc/sys/vm/min_free_kbytes
> 2730
> [root at Samsung ~]#
>
>
> When SECTION_SIZE_BITS is 28 (256MiB),
>
> [root at Samsung ~]# cat /proc/sys/vm/min_free_kbytes
> 2736
> [root at Samsung ~]# echo "2730" > /proc/sys/vm/min_free_kbytes
> Unable to handle kernel NULL pointer dereference at virtual address 00000004
> pgd = 80a14000
> [00000004] *pgd=20a0b031, *pte=00000000, *ppte=00000000
> Internal error: Oops: 17 [#1] PREEMPT
> last sysfs file:
> Modules linked in:
> CPU: 0    Not tainted  (2.6.35-rc4-00007-g9a59bf7-dirty #3)
> PC is at get_pageblock_flags_group+0x54/0xa8
> LR is at setup_per_zone_wmarks+0xfc/0x1d4
> pc : [<800686cc>]    lr : [<800691a0>]    psr: 60000093
> sp : 80a03ed0  ip : 00000001  fp : 00058000
> r10: 004a0000  r9 : 801e5fbc  r8 : 802c0000
> r7 : 0001c900  r6 : 00025000  r5 : 801e5fa4  r4 : 0000007e
> r3 : 00000018  r2 : 00000002  r1 : 00000000  r0 : 00000000
> Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
> Control: 10c5387d  Table: 20a14019  DAC: 00000015
> Process bash (pid: 888, stack limit = 0x80a022e8)
> Stack: (0x80a03ed0 to 0x80a04000)
> 3ec0:                                     00000000 801e5fa4 00025000
> 800691a0
> 3ee0: a0000013 000002aa 00000005 00000001 801d8254 2aacb000 00000005
> 00000001
> 3f00: 80a02000 80a03f80 00000001 80069354 80a03f80 00000001 801d7900
> 800d2734
> 3f20: 80a03f80 00000000 00000000 00000005 80a0903c 00000005 b7c81c00
> 2aacb000
> 3f40: 80a03f80 00000005 00000000 800d2760 00000001 2aacb000 00000005
> 8008ff74
> 3f60: b7c81c00 2aacb000 b7c81c00 2aacb000 00000000 00000000 00000005
> 800900c8
> 3f80: 00000005 00000000 00000005 00000000 00000005 2aacb000 2ac525f8
> 00000004
> 3fa0: 8001f0e8 8001ef40 00000005 2aacb000 00000001 2aacb000 00000005
> 00000000
> 3fc0: 00000005 2aacb000 2ac525f8 00000004 00000005 000babe0 00000000
> 00000001
> 3fe0: 2aacb000 7e88ca58 2ab99124 2abe643c 60000010 00000001 00000000
> 00000000
> [<800686cc>] (get_pageblock_flags_group+0x54/0xa8) from [<800691a0>]
> (setup_per_zone_wmarks+0xfc/0x1d4)
> [<800691a0>] (setup_per_zone_wmarks+0xfc/0x1d4) from [<80069354>]
> (min_free_kbytes_sysctl_handler+0x20/0x28)
> [<80069354>] (min_free_kbytes_sysctl_handler+0x20/0x28) from [<800d2734>]
> (proc_sys_call_handler+0x90/0xac)
> [<800d2734>] (proc_sys_call_handler+0x90/0xac) from [<800d2760>]
> (proc_sys_write+0x10/0x14)
> [<800d2760>] (proc_sys_write+0x10/0x14) from [<8008ff74>]
> (vfs_write+0xac/0x154)
> [<8008ff74>] (vfs_write+0xac/0x154) from [<800900c8>] (sys_write+0x3c/0x68)
> [<800900c8>] (sys_write+0x3c/0x68) from [<8001ef40>]
> (ret_fast_syscall+0x0/0x30)
> Code: 11a0cb8c 11a0cbac 1080018c e3a0c001 (e5904004)
> ---[ end trace 8b96cc6afed783d1 ]---
> note: bash[888] exited with preempt_count 1
> BUG: scheduling while atomic: bash/888/0x40000002
> Modules linked in:
> [<80024558>] (unwind_backtrace+0x0/0xec) from [<8014f110>]
> (schedule+0x6c/0x2e4)
> [<8014f110>] (schedule+0x6c/0x2e4) from [<80035f74>]
> (__cond_resched+0x24/0x34)
> [<80035f74>] (__cond_resched+0x24/0x34) from [<8014f484>]
> (_cond_resched+0x30/0x40)
> [<8014f484>] (_cond_resched+0x30/0x40) from [<8007ac1c>]
> (unmap_vmas+0x550/0x604)
> [<8007ac1c>] (unmap_vmas+0x550/0x604) from [<8007d6b8>]
> (exit_mmap+0xb0/0x1d8)
> [<8007d6b8>] (exit_mmap+0xb0/0x1d8) from [<80037de8>] (mmput+0x4c/0x104)
> [<80037de8>] (mmput+0x4c/0x104) from [<8003b7f4>] (exit_mm+0x104/0x10c)
> [<8003b7f4>] (exit_mm+0x104/0x10c) from [<8003cdc4>] (do_exit+0x194/0x5bc)
> [<8003cdc4>] (do_exit+0x194/0x5bc) from [<80022950>] (die+0x190/0x1bc)
> [<80022950>] (die+0x190/0x1bc) from [<80025488>]
> (__do_kernel_fault+0x64/0x84)
> [<80025488>] (__do_kernel_fault+0x64/0x84) from [<8002567c>]
> (do_page_fault+0x1d4/0x1ec)
> [<8002567c>] (do_page_fault+0x1d4/0x1ec) from [<8001e2d0>]
> (do_DataAbort+0x34/0x94)
> [<8001e2d0>] (do_DataAbort+0x34/0x94) from [<8001ea2c>]
> (__dabt_svc+0x4c/0x60)
> Exception stack(0x80a03e88 to 0x80a03ed0)
> 3e80:                   00000000 00000000 00000002 00000018 0000007e
> 801e5fa4
> 3ea0: 00025000 0001c900 802c0000 801e5fbc 004a0000 00058000 00000001
> 80a03ed0
> 3ec0: 800691a0 800686cc 60000093 ffffffff
> [<8001ea2c>] (__dabt_svc+0x4c/0x60) from [<800686cc>]
> (get_pageblock_flags_group+0x54/0xa8)
> [<800686cc>] (get_pageblock_flags_group+0x54/0xa8) from [<800691a0>]
> (setup_per_zone_wmarks+0xfc/0x1d4)
> [<800691a0>] (setup_per_zone_wmarks+0xfc/0x1d4) from [<80069354>]
> (min_free_kbytes_sysctl_handler+0x20/0x28)
> [<80069354>] (min_free_kbytes_sysctl_handler+0x20/0x28) from [<800d2734>]
> (proc_sys_call_handler+0x90/0xac)
> [<800d2734>] (proc_sys_call_handler+0x90/0xac) from [<800d2760>]
> (proc_sys_write+0x10/0x14)
> [<800d2760>] (proc_sys_write+0x10/0x14) from [<8008ff74>]
> (vfs_write+0xac/0x154)
> [<8008ff74>] (vfs_write+0xac/0x154) from [<800900c8>] (sys_write+0x3c/0x68)
> [<800900c8>] (sys_write+0x3c/0x68) from [<8001ef40>]
> (ret_fast_syscall+0x0/0x30)
> BUG: spinlock lockup on CPU#0, bash/888, 801e5fbc
> [<80024558>] (unwind_backtrace+0x0/0xec) from [<801098a8>]
> (do_raw_spin_lock+0x110/0x14c)
> [<801098a8>] (do_raw_spin_lock+0x110/0x14c) from [<8006963c>]
> (free_pcppages_bulk+0x24/0x2f4)
> [<8006963c>] (free_pcppages_bulk+0x24/0x2f4) from [<80069f28>]
> (free_hot_cold_page+0x15c/0x180)
> [<80069f28>] (free_hot_cold_page+0x15c/0x180) from [<8007b834>]
> (free_pgd_range+0x15c/0x17c)
> [<8007b834>] (free_pgd_range+0x15c/0x17c) from [<8007b8e4>]
> (free_pgtables+0x90/0x9c)
> [<8007b8e4>] (free_pgtables+0x90/0x9c) from [<8007d714>]
> (exit_mmap+0x10c/0x1d8)
> [<8007d714>] (exit_mmap+0x10c/0x1d8) from [<80037de8>] (mmput+0x4c/0x104)
> [<80037de8>] (mmput+0x4c/0x104) from [<8003b7f4>] (exit_mm+0x104/0x10c)
> [<8003b7f4>] (exit_mm+0x104/0x10c) from [<8003cdc4>] (do_exit+0x194/0x5bc)
> [<8003cdc4>] (do_exit+0x194/0x5bc) from [<80022950>] (die+0x190/0x1bc)
> [<80022950>] (die+0x190/0x1bc) from [<80025488>]
> (__do_kernel_fault+0x64/0x84)
> [<80025488>] (__do_kernel_fault+0x64/0x84) from [<8002567c>]
> (do_page_fault+0x1d4/0x1ec)
> [<8002567c>] (do_page_fault+0x1d4/0x1ec) from [<8001e2d0>]
> (do_DataAbort+0x34/0x94)
> [<8001e2d0>] (do_DataAbort+0x34/0x94) from [<8001ea2c>]
> (__dabt_svc+0x4c/0x60)
> Exception stack(0x80a03e88 to 0x80a03ed0)
> 3e80:                   00000000 00000000 00000002 00000018 0000007e
> 801e5fa4
> 3ea0: 00025000 0001c900 802c0000 801e5fbc 004a0000 00058000 00000001
> 80a03ed0
> 3ec0: 800691a0 800686cc 60000093 ffffffff
> [<8001ea2c>] (__dabt_svc+0x4c/0x60) from [<800686cc>]
> (get_pageblock_flags_group+0x54/0xa8)
> [<800686cc>] (get_pageblock_flags_group+0x54/0xa8) from [<800691a0>]
> (setup_per_zone_wmarks+0xfc/0x1d4)
> [<800691a0>] (setup_per_zone_wmarks+0xfc/0x1d4) from [<80069354>]
> (min_free_kbytes_sysctl_handler+0x20/0x28)
> [<80069354>] (min_free_kbytes_sysctl_handler+0x20/0x28) from [<800d2734>]
> (proc_sys_call_handler+0x90/0xac)
> [<800d2734>] (proc_sys_call_handler+0x90/0xac) from [<800d2760>]
> (proc_sys_write+0x10/0x14)
> [<800d2760>] (proc_sys_write+0x10/0x14) from [<8008ff74>]
> (vfs_write+0xac/0x154)
> [<8008ff74>] (vfs_write+0xac/0x154) from [<800900c8>] (sys_write+0x3c/0x68)
> [<800900c8>] (sys_write+0x3c/0x68) from [<8001ef40>]
> (ret_fast_syscall+0x0/0x30)
>
>
> Thanks.
>
> Best regards,
> Kgene.
> --
> Kukjin Kim <kgene.kim at samsung.com>, Senior Engineer,
> SW Solution Development Team, Samsung Electronics Co., Ltd.
>
> --
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