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SubjectRe: [RFC][PATCH] Fix area->nr_free-- went (-1) issue in buddy system
Hi Nick,

Thanks for your reply again, ;-).

On 12/19/06, Nick Piggin <> wrote:
> This should not happen because the pages are checked to ensure they are
> from the same zone before merging.

How? page_is_buddy() only check if the buddy has the buddy flag and
has the same order.
Where can I find the same zone is checked?

> What kind of system do you have? What is the dmesg and the .config?

I'm using the blackfin uclinux. dmesg and .config is attached.

> It could be that the zones are not properly aligned and CONFIG_HOLES_IN_ZONE
> is not set.

I changed the code in paging_init(), see below:
#if 0
zones_size[ZONE_DMA] = (end_mem - PAGE_OFFSET) >> PAGE_SHIFT;
zones_size[ZONE_NORMAL] = 0;
zones_size[ZONE_DMA] = (end_mem/2 - PAGE_OFFSET) >> PAGE_SHIFT;
zones_size[ZONE_NORMAL] = (end_mem/2 - PAGE_OFFSET) >>
This is only what I did the change. I also suspect the zones are not
properly aligned, But how to align it? I think our system doesn't need

root:~> dmesg
Linux version (aubrey@suse10) (gcc version 4.1.1 (ADI 06R2)) #2 Tue Dec 19 14:03:41 CST 2006
Blackfin support (C) 2004-2006 Analog Devices, Inc.
Compiled for ADSP-BF537 Rev. 0.2
Blackfin uClinux support by
Processor Speed: 500 MHz core clock and 100 Mhz System Clock
Board Memory: 48MB
Kernel Managed Memory: 48MB
Memory map:
text = 0x00001000-0x0011cd18
init = 0x0011d000-0x0012b9b0
data = 0x0012bfdc-0x00151aa4
stack = 0x0012c000-0x0012e000
bss = 0x00151ab0-0x001600b4
available = 0x001600b4-0x02700000
rootfs = 0x02700000-0x02f00000
DMA Zone = 0x02f00000-0x03000000
On node 0 totalpages: 9984
DMA zone: 4992 pages, LIFO batch:0
DMA32 zone: 0 pages, LIFO batch:0
Normal zone: 4992 pages, LIFO batch:0
HighMem zone: 0 pages, LIFO batch:0
Instruction Cache Enabled
Data Cache Enabled (write-through)
Hardware Trace Enabled
Built 1 zonelists
Kernel command line: root=/dev/mtdblock0 rw mem=48M ip=
Configuring Blackfin Priority Driven Interrupts
PID hash table entries: 256 (order: 8, 4096 bytes)
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
Physical pages: 2700
Memory available: 38144k/47952k RAM, (58k init code, 1135k kernel code, 57k data, 1024k dma)
Blackfin Scratchpad data SRAM: 4 KB
Blackfin DATA_A SRAM: 16 KB
Blackfin DATA_B SRAM: 16 KB
Blackfin Instruction SRAM: 48 KB
Calibrating delay loop... 995.32 BogoMIPS (lpj=1990656)
Security Framework v1.0.0 initialized
Capability LSM initialized
Mount-cache hash table entries: 512
NET: Registered protocol family 16
Blackfin DMA Controller
stamp_init(): registering device resources
NET: Registered protocol family 23
io scheduler noop registered
io scheduler anticipatory registered (default)
io scheduler cfq registered
Real Time Clock Driver v1.10e
Dynamic Power Management Controller Driver v0.1: major=10, minor = 254
Blackfin BF5xx serial driver version 2.00 (DMA mode)
RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
Blackfin mac net device registered
uclinux[mtd]: RAM probe address=0x2700000 size=0x800000
Creating 1 MTD partitions on "RAM":
0x00000000-0x00800000 : "ROMfs"
uclinux[mtd]: set ROMfs:EXT2 to be root filesystem
NET: Registered protocol family 2
IP route cache hash table entries: 512 (order: -1, 2048 bytes)
TCP established hash table entries: 2048 (order: 1, 8192 bytes)
TCP bind hash table entries: 2048 (order: 1, 8192 bytes)
TCP: Hash tables configured (established 2048 bind 2048)
TCP reno registered
TCP bic registered
NET: Registered protocol family 1
NET: Registered protocol family 17
IrCOMM protocol (Dag Brattli)
IP-Config: Gateway not on directly connected network.
VFS: Mounted root (ext2 filesystem).
Freeing unused kernel memory: 56k freed (0x11d000 - 0x12a000)
ttyS0 at irq = 18 is a builtin Blackfin UART
dma_alloc_init: dma_page @ 0x0242d000 - 256 pages at 0x02f00000
root:~> cat /proc/buddyinfo
Node 0, zone DMA 4 3 1 2 1 1 0 1 1 2 1 1 0 0
Node 0, zone Normal 3 1 2 2 1 1 0 0 4294967295 0 0 0 1 0
[unhandled content-type:application/x-config]
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