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@gmail.com> wrote:
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?
Only the first wirte trigger page fault, which setup the page table by 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.
-- Thanks Dhyan
On Wed, Aug 1, 2012 at 7:38 AM, bill4carson <bill4carson@gmail.com <mailto:bill4carson@gmail.com>**> 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@gmail.com <mailto:bill4carson@gmail.com> <mailto:bill4carson@gmail.com <mailto:bill4carson@gmail.com>**
__>
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 arch/arm/include/asm/pgtable._**___h.
|#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
-- Love each day!
--bill
-- Love each day!
--bill