The page_owner_sort tool fails to sort the page owner information.

Issue

• The page_owner_sort tool fails to sort the page owner information (/sys/kernel/debug/page_owner) captured from RHEL-8.7 (kernel 4.18.0-425.3.1.el8 and above)
  and RHEL-9.0 (kernel 5.14.0-70.13.1.el9 and above).

Red Hat Enterprise Linux 8.7

# uname -r
4.18.0-425.3.1.el8.x86_64

# ./anon_prog 
10 GB memory filled with 0 by memset()

# cat /sys/kernel/debug/page_owner > page_owner_full.txt

# grep -v ^PFN page_owner_full.txt > page_owner.txt

# page_owner_sort page_owner.txt sorted_page_owner.txt
loaded 3491534
sorting ....
culling

# head -n 20 sorted_page_owner.txt
12 times:
Page allocated via order 0, mask 0x6082c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_ZERO), pid 2, tgid 2 (kthreadd), ts 326107344 ns, free_ts 0 ns
 prep_new_page+0xe5/0x100
 get_page_from_freelist+0x1114/0x1360
 __alloc_pages_nodemask+0x166/0x320
 __vmalloc_node_range+0x135/0x230
 copy_process+0x8de/0x1bb0
 _do_fork+0x8b/0x340
 kernel_thread+0x25/0x30
 kthreadd+0x2a3/0x2f0
 ret_from_fork+0x35/0x40

4 times:
Page allocated via order 0, mask 0x6082c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_ZERO), pid 2, tgid 2 (kthreadd), ts 302417615 ns, free_ts 0 ns
 prep_new_page+0xe5/0x100
 get_page_from_freelist+0x1114/0x1360
 __alloc_pages_nodemask+0x166/0x320
 __vmalloc_node_range+0x135/0x230
 copy_process+0x8de/0x1bb0
 _do_fork+0x8b/0x340

• The page_owner_sort tool shows the expected result for the page owner information captured from RHEL-8.6 (kernel 4.18.0-372.70.1.el8_6 and below).

Red Hat Enterprise Linux 8.6 
**************************** 
# uname -r
4.18.0-372.70.1.el8_6.x86_64

# ./anon_prog 
10 GB memory filled with 0 by memset()

# cat /sys/kernel/debug/page_owner > page_owner_full.txt

# grep -v ^PFN page_owner_full.txt > page_owner.txt

# page_owner_sort page_owner.txt sorted_page_owner.txt
loaded 49461
sorting ....
culling

# head -n 17 sorted_page_owner.txt
2621440 times:
Page allocated via order 0, mask 0x6200ca(GFP_HIGHUSER_MOVABLE)
 prep_new_page+0xe5/0x100
 get_page_from_freelist+0x1114/0x1360
 __alloc_pages_nodemask+0x166/0x320
 alloc_pages_vma+0x74/0x1d0
 shmem_alloc_page+0x47/0x90
 shmem_alloc_and_acct_page+0x76/0x1c0
 shmem_getpage_gfp+0x16f/0x8a0
 shmem_fault+0x78/0x220
 __do_fault+0x38/0xc0
 handle_pte_fault+0x491/0x880
 __handle_mm_fault+0x453/0x6c0
 handle_mm_fault+0xc1/0x1e0
 do_user_addr_fault+0x1b9/0x450
 do_page_fault+0x37/0x130
 page_fault+0x1e/0x30

- Page allocated via order 0
- Memory allocation times is 2621440

# bc -q
scale=2
2621440*4/2^20
10.00 (GiB)