On Fri, Oct 1, 2010 at 5:01 PM, luca ellero <lroluk@xxxxxxxxx> wrote:
> Il 01/10/2010 9.51, Arun KS wrote:
>>
>> Hello,
>>
>> kmalloc() memory is reserved or not?
>
> No, kmalloc memory is not reserved. The buddy allocator, which is eventually
> used by kmalloc, use only pages NOT reserved and don't mark the pages
> "reserved" when these are allocated.
If reserved is not set, how kernel knows that these pages are swappable or not?
AFAIK kernel memory is non-swappable. So we have to mark it reserved.
Or there is another mechanism to attain this?
> In other words "reserved" bit is set only during boot time and I don't think
> is ever modified later.
>
>> I tried to print the amount of reserved memory before and after
>> allocating 10 MB of memory using kmalloc(). But both shows the same.
>>
>> Here is the code,
>>
>> #include <linux/module.h>
>> #include <linux/moduleparam.h>
>> #include <linux/init.h>
>>
>> #include <linux/kernel.h>
>> #include <linux/slab.h>
>> #include <linux/fs.h>
>> #include <linux/errno.h>
>> #include <linux/types.h>
>> #include <linux/mm.h>
>> #include <linux/kdev_t.h>
>> #include <asm/page.h>
>> #include <asm/memory.h>
>> #include <linux/cdev.h>
>> #include <linux/device.h>
>>
>> static int check_memory(void)
>> {
>> int i ;
>> int temp = 0;
>> int reserved;
>> struct page * pp;
>> unsigned long reserved_pages=0;
>>
>> i = virt_to_phys(0xc0000000);
>> i >>= PAGE_SHIFT;
>>
>> while (pfn_valid(i)) {
>>
>> pp = pfn_to_page(i);
>>
>> reserved = PageReserved(pp);
>> if(reserved)
>> reserved_pages++;
>>
>> if ( ( temp != reserved ) || ( i == 0 ) )
>> printk("%08x reserved: %s\n", i << PAGE_SHIFT,
>> reserved? "yes": "no");
>>
>> temp = reserved;
>> ++i;
>> }
>> printk("number of reserved pages = %d\n", reserved_pages);
>> printk("total memory used by kernel = %d\n", reserved_pages*(1
>> << PAGE_SHIFT));
>> return 0;
>> }
>>
>> static int simple_init(void)
>> {
>> int i;
>>
>> check_memory();
>>
>> /* Allocating 10MB of memory */
>> for ( i = 0 ; i < 2560 ; i ++){
>> if( kmalloc(4096, GFP_KERNEL) == NULL)
>> printk("cannot alocate memory %d\n", i);
>> }
>>
>> check_memory();
>>
>> return 0;
>> }
>>
>> static void simple_cleanup(void)
>> {
>> }
>>
>> module_init(simple_init);
>> module_exit(simple_cleanup);
>>
>> Any Idea?
>>
>> Here is the output.
>>
>> <4>[ 309.065732] number of reserved pages = 13009
>> <4>[ 309.065746] total memory used by kernel = 53284864
>> <4>[ 321.214470] number of reserved pages = 13009
>> <4>[ 321.214483] total memory used by kernel = 53284864
>>
>> Arun
>>
>> On Wed, Sep 29, 2010 at 12:43 AM, Arun KS <getarunks@xxxxxxxxx
>> <mailto:getarunks@xxxxxxxxx>> wrote:
>>
>> Just updating our simple_module to work on all the machines,
>>
>> #include <linux/module.h>
>> #include <linux/moduleparam.h>
>> #include <linux/init.h>
>>
>> #include <linux/kernel.h>
>> #include <linux/slab.h>
>> #include <linux/fs.h>
>> #include <linux/errno.h>
>> #include <linux/types.h>
>> #include <linux/mm.h>
>> #include <linux/kdev_t.h>
>> #include <asm/page.h>
>> #include <asm/memory.h>
>> #include <linux/cdev.h>
>> #include <linux/device.h>
>>
>> static int simple_init(void)
>> {
>> int i ;
>> int temp = 0;
>> int reserved;
>> struct page * pp;
>> unsigned long reserved_pages=0;
>>
>> i = virt_to_phys(0xc0000000);
>> i >>= PAGE_SHIFT;
>>
>> while (pfn_valid(i)) {
>>
>> pp = pfn_to_page(i);
>>
>> reserved = PageReserved(pp);
>> if(reserved)
>> reserved_pages++;
>>
>> if ( ( temp != reserved ) || ( i == 0 ) )
>> printk("%08x reserved: %s\n", i << PAGE_SHIFT,
>> reserved? "yes": "no");
>>
>> temp = reserved;
>> ++i;
>> }
>> printk("number of reserved pages = %d\n", reserved_pages);
>> printk("total memory used by kernel in bytes = %d\n",
>> reserved_pages*(1 << PAGE_SHIFT));
>> return 0;
>> }
>>
>> static void simple_cleanup(void)
>> {
>> }
>>
>> module_init(simple_init);
>> module_exit(simple_cleanup);
>>
>> Thanks,
>> Arun
>>
>> On Tue, Sep 28, 2010 at 2:47 PM, Arun KS <getarunks@xxxxxxxxx
>> <mailto:getarunks@xxxxxxxxx>> wrote:
>> > Hi Dave,
>> >
>> > Thanks for your reply.
>> >
>> > On Tue, Sep 28, 2010 at 1:00 PM, Dave Hylands <dhylands@xxxxxxxxx
>> <mailto:dhylands@xxxxxxxxx>> wrote:
>> >> Hi Arun,
>> >>
>> >>>> I can definitely confirm that not all ARM processors start
>> their RAM
>> >>>> at physical address zero.
>> >>>>
>> >>>> If you have a kernel module (or you can rebuild your kernel to
>> add a
>> >>>> printk), you can have it print out the 4 bytes at virtual address
>> >>>> 0xC0004000. The top 3 nibbles of this first word will be the top
>> 3
>> >>>> nibbles of the physical address of your first page of memory.
>> >>>>
>> >>>> So, something like:
>> >>>>
>> >>>> printk( "0x%08x\n", *(uint32_t *)0xc0004000 );
>> >>>
>> >>> I tried printing,
>> >>>
>> >>> printk( "0x%08x\n", *(uint32_t *)0xc0004000 );
>> >>> printk("0x%08x\n", virt_to_phys(0xc0004000));
>> >>>
>> >>> Output:
>> >>> 0x00000000
>> >>> 0x13004000
>> >>
>> >> Ok - so this tells me that your SDRAM starts at 0x13000000
>> >>
>> >> I realized that printing 0xc0004000 corresponds to memory
>> location zero.
>> >>
>> >> What we really wanted was the MMU entry which correponds to virtual
>> >> address 0xc0000000. The high 3 nibbles is 0xc00, so we would have
>> >> needed to do
>> >>
>> >> printk( "0x%08x\n", *(uint32_t *)(0xc0004000 + ( 0xc00 * 4 ));
>> >>
>> >> and that should print
>> >>
>> >> 0x130xxxxx
>> >>
>> >>> So I initialized the variable "i" in the kernel module to
>> 0x13004000.
>> >>> But still it is not entering the while loop.
>> >>
>> >> PFN's are equal to the physical address shifted right by 20.
>> >
>> > Is this value 12?
>> >
>> >>
>> >> So the PFN for 0x13004000 would be 0x130 or 304 (base 10)
>> >
>> > so PFN is 0x13004
>> >
>> > Here is the output of the module when i is initialized to 0x13004.
>> >
>> > <4>[ 1647.455344] 13004000 reserved: yes
>> > <4>[ 1647.455373] 13008000 reserved: no
>> > <4>[ 1647.455414] 1302c000 reserved: yes
>> > <4>[ 1647.456213] 136b4000 reserved: no
>> > <4>[ 1647.456241] 136b6000 reserved: yes
>> > <4>[ 1647.456461] 1385a000 reserved: no
>> > <4>[ 1647.457838] 143c5000 reserved: yes
>> > <4>[ 1647.462746] 16bf2000 reserved: no
>> > <4>[ 1647.462783] 16c00000 reserved: yes
>> > <4>[ 1647.463083] 16e50000 reserved: no
>> > <4>[ 1647.478204] 1ea0c000 reserved: yes
>> > <4>[ 1647.478246] 1ea0f000 reserved: no
>> > <4>[ 1647.478304] 1ea56000 reserved: yes
>> > <4>[ 1647.478331] 1ea57000 reserved: no
>> > <4>[ 1647.478391] 1eaa1000 reserved: yes
>> > <4>[ 1647.478416] 1eaa2000 reserved: no
>> > <4>[ 1647.478443] 1eaa3000 reserved: yes
>> > <4>[ 1647.478468] 1eaa4000 reserved: no
>> > <4>[ 1647.478499] 1eab0000 reserved: yes
>> > <4>[ 1647.478529] 1eab9000 reserved: no
>> > <4>[ 1647.480438] 1f9c0000 reserved: yes
>> > <4>[ 1647.480471] 1f9c9000 reserved: no
>> > <4>[ 1647.480591] 1fa94000 reserved: yes
>> > <4>[ 1647.480618] 1fa95000 reserved: no
>> > <4>[ 1647.480651] 1faa8000 reserved: yes
>> > <4>[ 1647.480678] 1faa9000 reserved: no
>> > <4>[ 1647.480756] 1fb1c000 reserved: yes
>> > <4>[ 1647.480784] 1fb20000 reserved: no
>> > <4>[ 1647.480826] 1fb46000 reserved: yes
>> > <4>[ 1647.480853] 1fb47000 reserved: no
>> > <4>[ 1647.480921] 1fba4000 reserved: yes
>> > <4>[ 1647.480948] 1fba6000 reserved: no
>> > <4>[ 1647.481391] 1ff28000 reserved: yes
>> > <4>[ 1647.481418] 1ff2b000 reserved: no
>> >
>> > Thanks for everyone. This helped me. :-)
>> >
>> > Arun
>> >
>> >>
>> >>> Makefile.boot is saying
>> >>>
>> >>> zreladdr-y := 0x13008000
>> >>> params_phys-y := 0x13000100
>> >>
>> >> This further confirms that physical memory starts at 0x13000000
>> >>
>> >> --
>> >> Dave Hylands
>> >> Shuswap, BC, Canada
>> >> http://www.DaveHylands.com/
>> >>
>> >
>>
>>
>
>
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