Re: [PATCH v3] arm64/x86_64: show zero pfn information when using vtop

[lijiang <lijiang@xxxxxxxxxx>]

On Thu, May 25, 2023 at 7:27 AM Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx> wrote:

On 2023/5/24 22:18, lijiang wrote:

Hi, Rongwei

Thank you for the patch.

On Tue, May 16, 2023 at 8:00 PM <crash-utility-request@xxxxxxxxxx> wrote:

Date: Tue, 16 May 2023 19:40:54 +0800
From: Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx>
To: crash-utility@xxxxxxxxxx,   k-hagio-ab@xxxxxxx
Subject: [PATCH v3] arm64/x86_64: show zero pfn
        information when using vtop
Message-ID: <20230516114054.63844-1-rongwei.wang@xxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset="US-ASCII"; x-default=true

Now vtop can not show us the page is zero pfn
when PTE or PMD has attached ZERO PAGE. This
patch supports show this information directly
when using vtop, likes:

crash> vtop -c 13674 ffff8917e000
VIRTUAL     PHYSICAL
ffff8917e000  836e71000

PAGE DIRECTORY: ffff000802f8d000
   PGD: ffff000802f8dff8 => 884e29003
   PUD: ffff000844e29ff0 => 884e93003
   PMD: ffff000844e93240 => 840413003
   PTE: ffff000800413bf0 => 160000836e71fc3
  PAGE: 836e71000  (ZERO PAGE)
...

If huge page found:

crash> vtop -c 14538 ffff95800000
VIRTUAL     PHYSICAL
ffff95800000  910c00000

PAGE DIRECTORY: ffff000801fa0000
   PGD: ffff000801fa0ff8 => 884f53003
   PUD: ffff000844f53ff0 => 8426cb003
   PMD: ffff0008026cb560 => 60000910c00fc1
  PAGE: 910c00000  (2MB, ZERO PAGE)
...

I did some tests on x86 64 and aarch64 machines, and got the following results.

[1] on x86 64, it does not print the "ZERO PAGE" when using 1G huge pages. (but for 2M huge page, it works)

crash> vtop -c 2763 7fdfc0000000
VIRTUAL     PHYSICAL        
7fdfc0000000  300000000      

   PGD: 23b9ae7f8 => 8000000235031067
   PUD: 235031bf8 => 80000003000008e7
  PAGE: 300000000  (1GB)

      PTE         PHYSICAL   FLAGS
80000003000008e7  300000000  (PRESENT|RW|USER|ACCESSED|DIRTY|PSE|NX)

      VMA           START       END     FLAGS FILE
ffff9d65fc8a85c0 7fdfc0000000 7fe000000000 84400fb /mnt/hugetlbfs/test

      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffef30cc000000 300000000 ffff9d65f5c35850        0  2 57ffffc001000c uptodate,dirty,head

crash> help -v|grep zero
         zero_paddr: 221a37000
    huge_zero_paddr: 240000000

[2] on aarch64, it does not print the "ZERO PAGE"

crash> vtop -c 23390 ffff8d600000
VIRTUAL     PHYSICAL        
ffff8d600000  cc800000        

PAGE DIRECTORY: ffff224ba02d9000
   PGD: ffff224ba02d9ff8 => 80000017b38f003
   PUD: ffff224b7b38fff0 => 80000017b38e003
   PMD: ffff224b7b38e358 => e80000cc800f41
  PAGE: cc800000  (2MB)

     PTE        PHYSICAL  FLAGS
e80000cc800f41  cc800000  (VALID|USER|SHARED|AF|NG|PXN|UXN|DIRTY)

      VMA           START       END     FLAGS FILE
ffff224bb315f678 ffff8d600000 ffff8d800000 4400fb /mnt/hugetlbfs/test

      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
fffffc892b320000  cc800000 ffff224b5c48ac90        0  2 7ffff80001000c uptodate,dirty,head
crash> help -v|grep zero
         zero_paddr: 142662000
    huge_zero_paddr: 111400000

I have one question:  can this patch print "ZERO PAGE" on x86 64 when using 1G huge pages? Or is it expected behavior on x86 64?

And It does not work on aarch64 machine to me. Did I miss anything else?

Hi, lijiang

I find you use '/mnt/hugetlbfs/test' to test this patch, but I have not do this on hugetlbfs, just support THP (I

You are right, Rongwei. Because the z.c test case does not work on my machines, I wrote two test cases by myself.

z.c: https://listman.redhat.com/archives/crash-utility/2023-May/010666.html

my test cases:

[1] use the mmap() to map the memory(without the *MAP_HUGETLB* flag):

ptr = mmap(NULL, map_len, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

[2] use the madvise() as below:

posix_memalign(&ptr, huge_page_size, n);

madvise(ptr, n, MADV_HUGEPAGE);

And then read data from ptr, the [1] and [2] both can work on my X86 64 machines for 2M hugepage.

But for the 1G hugepage, I did not see the similar code change in your patch, do you mean that this patch doesn't support for the 1G hugepage?

I can confirm that the 1G hugepage is supported on my X86 64 machine:

# cat /proc/meminfo |grep -i huge
AnonHugePages:    407552 kB
ShmemHugePages:        0 kB
FileHugePages:     63488 kB
HugePages_Total:      10
HugePages_Free:       10
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:    1048576 kB
Hugetlb:        10485760 kB

indeed ignore the hugetlb when coding this function).

And I have read mm/hugetlb.c roughly, not find any zero page stuff when page fault with read. It seems that hugetlb is not an angel user of this function.

If the current patch does not support printing "ZERO PAGE" information when using hugetlbfs, it should be good to describe it in patch log(and explain a bit *why* if possible).

If I miss something, please let me know.

BTW: could you please check the z.c test case again? Or can you share your steps in detail, that can help me speed up the tests on X86 64(4k/2M/1G) and aarch64(4k or 64k/2M/512M/1G) machines.

# gcc -o z z.c
[root@hp-z640-01 crash]# ./z
zero: 7efe4cbff010  ---seems the address is problematic, not aligned
hello

 

Thanks.

Lianbo

Thanks for your time!

-wrw

Thanks

Lianbo

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