Dear Bill,
What i found from experimenting on arm Linux kernel is ,after every access if i clear the _PG_ACCESS bit of the pte (using /proc/<pid>/clear_refs),the next write also will come to kernel (handle_pte_fault).But I dont know whether my clearing action causing any bad impact on any other system.
--
Thanks
Dhyan
On Thu, Aug 2, 2012 at 2:12 PM, bill4carson <bill4carson@xxxxxxxxx> wrote:
What i found from experimenting on arm Linux kernel is ,after every access if i clear the _PG_ACCESS bit of the pte (using /proc/<pid>/clear_refs),the next write also will come to kernel (handle_pte_fault).But I dont know whether my clearing action causing any bad impact on any other system.
--
Thanks
Dhyan
On Thu, Aug 2, 2012 at 2:12 PM, bill4carson <bill4carson@xxxxxxxxx> wrote:
Only the first wirte trigger page fault, which setup the page table by
On 2012年08月01日 12:53, Dhyan wrote:
Dear Bill,
Thank you for spending your valuable time for understanding and
answering my queries !!!
I was trying to apply some garbage collection algorithm on this dumped
pages,thats why i want only the written pages.
Sorry to ask,but is there any other good way to find the written pages
of a user process?
grabbing a physical page to backup virtual address page. After this,
all write into that page goes like wind without any kernel interference
anymore.
But my hunch tell me what you want is to track every user space write
operation.
<mailto:bill4carson@xxxxxxxxx <mailto:bill4carson@xxxxxxxxx>>__><mailto:bill4carson@xxxxxxxxx>> wrote:
On 2012年07月31日 17:20, Dhyan wrote:
Thank You Bill !!!
I dont know my approach is correct or not,But the actual purpose
was to
dump only written pages of a user process using a kernel
module.I have
a kernel thread which will dump user process memory in specific
interval.So i thought of updating this flag (L_PTE_DEBUG) from
handle_pte_fault and clear from my clear thread so that i can
dump only
the written pages after my last dump.
Yes, you can do that, only if your accounting memory doesn't get swapped
out.
If I understand correctly, when writing a page, you mark corresponding
linux pte entry with L_PTE_DEBUG. Then your kernel module periodically
loops all linux pte table, find pte entry marked with L_PTE_DEBUG.....
I don't think it's wise to do so, you have 768 1st level pgd entries
for user space, followed by 256 pte entries with each pgd entry.
it's much slower to find out the right one.
moreover, you probably need to remap those L_PTE_DEBUG physical pages
into your own current process address space. IMHO, I don't follow
such idea could be feasible.
if you have some suggestions could you please share wth me?
I understand how you plan to do this, could I ask why you need to dump
the written pages?
--
Thanks
Dhyan
On Tue, Jul 31, 2012 at 12:43 PM, bill4carson
<bill4carson@xxxxxxxxx <mailto:bill4carson@xxxxxxxxx>arch/arm/include/asm/pgtable.____h.
wrote:
On 2012年07月30日 17:39, Dhyan wrote:
Dear All,
From linux(2.6.35) arm page table architecture i can
see we
have one
hardware page table and there is corresponding Linux
page table
Entry
(L_PTE_*).The "Linux" PTE definitions are as like below
from___________________________________________________
|#define L_PTE_PRESENT (1<< 0)
#define L_PTE_FILE (1<< 1)
#define L_PTE_YOUNG (1<< 1)
#define L_PTE_BUFFERABLE(1<< 2)
#define L_PTE_CACHEABLE (1<< 3)
#define L_PTE_USER (1<< 4)
#define L_PTE_WRITE (1<< 5)
#define L_PTE_EXEC (1<< 6)
#define L_PTE_DIRTY (1<< 7)
#define L_PTE_COHERENT (1<< 9)
#define L_PTE_SHARED (1<< 10)
|
So is it possible to add one more #|define L_PTE_DEBUG
(1 <<
11)| for my
debugging purpose (basically to trap all the write to
that page
and set
this bit when write happens and clear it off in another
thread
)? Or
is there any limitation like we can use only L_PTE till
10th bit ?
No such limitation on bit 11, so you can use define
L_PTE_DEBUG (1
<< 11)
However I don't follow why you want to do so?
So could you please help
--
Thanks & Regards
Dhayn
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Love each day!
--bill
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Love each day!
--bill
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Love each day!
--bill
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