[PATCH v2 0/2] Add support for getting page info of ZONE_DEVICE by /proc/kpage*

[sxwjean]

From: Xiongwei Song <sxwjean@xxxxxxxxx>

Patch 1 is adding pfn_to_devmap_page() function to get page of ZONE_DEVICE
by pfn. It checks if dev_pagemap is valid, if yes, return page pointer.

Patch 2 is finishing supporting /proc/kpage* in exposing pages info of
ZONE_DEVICE to userspace.

The unit test has been done by "page-types -r", which ran in qemu with the
below arguments:
    -object memory-backend-file,id=mem2,share,mem-path=./virtio_pmem.img,size=2G
    -device virtio-pmem-pci,memdev=mem2,id=nv1
, which is used to emulate pmem device with 2G memory space.

As we know, the pages in ZONE_DEVICE are only set PG_reserved flag. So
before the serires,
	run "page-types -r", the result is:
	             flags      page-count       MB  symbolic-flags                     long-symbolic-flags
	0x0000000100000000           24377       95  ___________________________r________________       reserved
	, which means the only PG_reserved set of pages in system wide have 24377.
	
	run "cat /proc/zoneinfo" to get the ZONE_DEVICE info:
	Node 1, zone   Device
	    pages free     0
	    boost    0
	    min      0
	    low      0
	    high     0
	    spanned  0
	    present  0
	    managed  0
	    cma      0
	    protection: (0, 0, 0, 0, 0)

After this series,
	run "page-types -r", the result is:
	             flags      page-count       MB  symbolic-flags                     long-symbolic-flags
	0x0000000100000000          548665     2143  ___________________________r________________       reserved
	, which means the only PG_reserved set of pages in system wide have 548665.
	
	Run "cat /proc/zoneinfo" to get the ZONE_DEVICE info:
	Node 1, zone   Device
	pages free     0
	    boost    0
	    min      0
	    low      0
	    high     0
	    spanned  524288
	    present  0
	    managed  0
	    cma      0
	    protection: (0, 0, 0, 0, 0)

, these added pages number is 524288 in ZONE_DEVICE as spanned field
showed. Meanwhile, we can do 548665 - 24377 = 524288 that is increment
of the reserved pages, it equals to the spanned field of ZONE_DEVICE.
Hence it looks like the patchset works well.

v1 -> v2:
  * Take David's suggestion to simplify the implementation of
    pfn_to_devmap_page(). Please take a look at
    https://lkml.org/lkml/2022/1/10/320 .

Xiongwei Song (2):
  mm/memremap.c: Add pfn_to_devmap_page() to get page in ZONE_DEVICE
  proc: Add getting pages info of ZONE_DEVICE support

 fs/proc/page.c           | 35 ++++++++++++++++++++-------------
 include/linux/memremap.h |  8 ++++++++
 mm/memremap.c            | 42 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 13 deletions(-)

-- 
2.30.2