tools/vm/page_owner_sort.c: support for user-defined culling rules

When viewing page owner information, we may want to cull blocks of
information with our own rules.  So it is important to enhance culling
function to provide the support for customizing culling rules.
Therefore, following adjustments are made:

1. Add --cull option to support the culling of blocks of information
   with user-defined culling rules.

	./page_owner_sort <input> <output> --cull=<rules>
	./page_owner_sort <input> <output> --cull <rules>

  <rules> is a single argument in the form of a comma-separated list to
  specify individual culling rules, by the sequence of keys k1,k2, ....
  Mixed use of abbreviated and complete-form of keys is allowed.

  For reference, please see the document(Documentation/vm/page_owner.rst).

Now, assuming two blocks in the input file are as follows:

	Page allocated via order 0, mask xxxx, pid 1, tgid 1 (task_name_demo)
	PFN xxxx
	 prep_new_page+0xd0/0xf8
	 get_page_from_freelist+0x4a0/0x1290
	 __alloc_pages+0x168/0x340
	 alloc_pages+0xb0/0x158

	Page allocated via order 0, mask xxxx, pid 32, tgid 32 (task_name_demo)
	PFN xxxx
	 prep_new_page+0xd0/0xf8
	 get_page_from_freelist+0x4a0/0x1290
	 __alloc_pages+0x168/0x340
	 alloc_pages+0xb0/0x158

If we want to cull the blocks by stacktrace and task command name, we can
use this command:

	./page_owner_sort <input> <output> --cull=stacktrace,name

The output would be like:

	2 times, 2 pages, task_comm_name: task_name_demo
	 prep_new_page+0xd0/0xf8
	 get_page_from_freelist+0x4a0/0x1290
	 __alloc_pages+0x168/0x340
	 alloc_pages+0xb0/0x158

As we can see, these two blocks are culled successfully, for they share
the same pid and task command name.

However, if we want to cull the blocks by pid, stacktrace and task command
name, we can this command:

	./page_owner_sort <input> <output> --cull=stacktrace,name,pid

The output would be like:

	1 times, 1 pages, PID 1, task_comm_name: task_name_demo
	 prep_new_page+0xd0/0xf8
	 get_page_from_freelist+0x4a0/0x1290
	 __alloc_pages+0x168/0x340
	 alloc_pages+0xb0/0x158

	1 times, 1 pages, PID 32, task_comm_name: task_name_demo
	 prep_new_page+0xd0/0xf8
	 get_page_from_freelist+0x4a0/0x1290
	 __alloc_pages+0x168/0x340
	 alloc_pages+0xb0/0x158

As we can see, these two blocks are failed to cull, for their PIDs are
different.

2. Add explanations of --cull options to the document.

This work is coauthored by
	Yixuan Cao
	Shenghong Han
	Yinan Zhang
	Chongxi Zhao
	Yuhong Feng

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jiajian Ye <[email protected]>
Cc: Yixuan Cao <[email protected]>
Cc: Shenghong Han <[email protected]>
Cc: Yinan Zhang <[email protected]>
Cc: Chongxi Zhao <[email protected]>
Cc: Yuhong Feng <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Sean Anderson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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