[Linux Kernel Memory Management] Partition Partner Allocator ⑥ (Related members of waterline control in zone structure | View memory area watermark in Ubuntu)

The previous blog [Linux Kernel Memory Management] Partition Partner Allocator ⑤ (Zone Watermark | Zone Watermark Data Structure zone_watermarks Enumeration | Zone Watermark Member in Memory Zone Zone) The concept of zone watermark is explained in this article. The blog starts to analyze the mechanism of water level control according to the water line;

WMARK_HIGHhigh water level, WMARK_LOWlow water level, WMARK_MINminimum water level, $3$ watermarks, dividing the "memory area" into$4$ parts;

enum zone_watermarks {
    
    
	WMARK_MIN,
	WMARK_LOW,
	WMARK_HIGH,
	NR_WMARK
};

#define min_wmark_pages(z) (z->watermark[WMARK_MIN])
#define low_wmark_pages(z) (z->watermark[WMARK_LOW])
#define high_wmark_pages(z) (z->watermark[WMARK_HIGH])

Source code path: linux-4.12\include\linux\mmzone.h #255

1. Waterline control related members in the zone structure ( managed_pages | spanned_pages | present_pages )

---

In the structure describing the "memory area" struct zonein , there are several important parameters for controlling the water level of the area :

managed_pagesMember represents the number of physical partner allocator ; it is calculated using the following formula:

$$\mathrm{z}\mathrm{o}\mathrm{n}\mathrm{e}\_\mathrm{e}\mathrm{n}\mathrm{d}\_\mathrm{p}\mathrm{f}\mathrm{n}-\mathrm{z}\mathrm{o}\mathrm{n}\mathrm{e}\_\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}\mathrm{t}\_\mathrm{p}\mathrm{f}\mathrm{n}$$

spanned_pagesThe member represents the number of all available physical pages in the memory area , including memory holes; it is calculated using the following formula:

$$\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{n}\mathrm{n}\mathrm{e}\mathrm{d}\_\mathrm{p}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{s}-\mathrm{h}\mathrm{o}\mathrm{l}\mathrm{e}\_\mathrm{p}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{s}$$

present_pagesThe member represents the number of physical pages in the current memory area , excluding memory holes; it is the physical page managed by the partner allocator; it is calculated using the following formula:

$$\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{n}\mathrm{t}\_\mathrm{p}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{s}-\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{d}\_\mathrm{p}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{s}$$

present_pages, spanned_pages, and the managed_pages three have the following relationship :

spanned_pages(all available physical pages in the memory region have holes) >
present_pages(the number of physical pages in the current region has no holes) >
managed_pages(the number of physical pages managed by the partner allocator)

Refer to [Linux Kernel Memory Management] Physical Memory Organization Structure ④ (Introduction to Memory Zone Zone | Zone Structure Source Code Analysis | Zone Structure Source Code) blog;

struct zoneStructure related source code:

struct zone {
    
    
	/* Read-mostly fields */

	/* zone watermarks, access with *_wmark_pages(zone) macros */
	unsigned long watermark[NR_WMARK];
	...
	
	unsigned long		managed_pages;
	unsigned long		spanned_pages;
	unsigned long		present_pages;
	...
}

Source code path: linux-4.12\include\linux\mmzone.h #427

2. View the memory area watermark in Ubuntu

---

From the Ubuntu command line, execute

cat /proc/zoneinfo

command, to view "memory area" information;

In the output, the information in the Normal area is as follows:

Node 0, zone   Normal
  pages free     5754
        min      4615
        low      5768
        high     6921
        spanned  262144
        present  262144
        managed  236760
        protection: (0, 0, 0, 0, 0)

The information of the DMA32 area is as follows:

Node 0, zone    DMA32
  pages free     43834
        min      12202
        low      15252
        high     18302
        spanned  1044480
        present  782288
        managed  759709
        protection: (0, 0, 924, 924, 924)

The information of the DMA area is as follows:

Node 0, zone      DMA
  per-node stats
      nr_inactive_anon 10820
      nr_active_anon 320858
      nr_inactive_file 231022
      nr_active_file 234555
      nr_unevictable 16
      nr_slab_reclaimable 44884
      nr_slab_unreclaimable 18674
      nr_isolated_anon 0
      nr_isolated_file 0

Complete output:

han@ubuntu:~$ cat /proc/zoneinfo
Node 0, zone      DMA
  per-node stats
      nr_inactive_anon 10820
      nr_active_anon 320858
      nr_inactive_file 231022
      nr_active_file 234555
      nr_unevictable 16
      nr_slab_reclaimable 44884
      nr_slab_unreclaimable 18674
      nr_isolated_anon 0
      nr_isolated_file 0
      workingset_nodes 0
      workingset_refault 0
      workingset_activate 0
      workingset_restore 0
      workingset_nodereclaim 0
      nr_anon_pages 320578
      nr_mapped    153680
      nr_file_pages 476705
      nr_dirty     26878
      nr_writeback 0
      nr_writeback_temp 0
      nr_shmem     11129
      nr_shmem_hugepages 0
      nr_shmem_pmdmapped 0
      nr_file_hugepages 0
      nr_file_pmdmapped 0
      nr_anon_transparent_hugepages 0
      nr_unstable  0
      nr_vmscan_write 0
      nr_vmscan_immediate_reclaim 0
      nr_dirtied   287542
      nr_written   244390
      nr_kernel_misc_reclaimable 0
  pages free     3968
        min      77
        low      96
        high     115
        spanned  4095
        present  3997
        managed  3976
        protection: (0, 2445, 3369, 3369, 3369)
      nr_free_pages 3968
      nr_zone_inactive_anon 0
      nr_zone_active_anon 0
      nr_zone_inactive_file 0
      nr_zone_active_file 0
      nr_zone_unevictable 0
      nr_zone_write_pending 0
      nr_mlock     0
      nr_page_table_pages 0
      nr_kernel_stack 0
      nr_bounce    0
      nr_zspages   0
      nr_free_cma  0
      numa_hit     1
      numa_miss    0
      numa_foreign 0
      numa_interleave 0
      numa_local   1
      numa_other   0
  pagesets
    cpu: 0
              count: 0
              high:  0
              batch: 1
  vm stats threshold: 6
    cpu: 1
              count: 0
              high:  0
              batch: 1
  vm stats threshold: 6
    cpu: 2
              count: 0
              high:  0
              batch: 1
  vm stats threshold: 6
    cpu: 3
              count: 0
              high:  0
              batch: 1
  vm stats threshold: 6
  node_unreclaimable:  0
  start_pfn:           1
Node 0, zone    DMA32
  pages free     43834
        min      12202
        low      15252
        high     18302
        spanned  1044480
        present  782288
        managed  759709
        protection: (0, 0, 924, 924, 924)
      nr_free_pages 43834
      nr_zone_inactive_anon 8454
      nr_zone_active_anon 245858
      nr_zone_inactive_file 181846
      nr_zone_active_file 177532
      nr_zone_unevictable 4
      nr_zone_write_pending 26534
      nr_mlock     4
      nr_page_table_pages 5641
      nr_kernel_stack 8472
      nr_bounce    0
      nr_zspages   0
      nr_free_cma  0
      numa_hit     4159869
      numa_miss    0
      numa_foreign 0
      numa_interleave 192366
      numa_local   4159869
      numa_other   0
  pagesets
    cpu: 0
              count: 50
              high:  378
              batch: 63
  vm stats threshold: 36
    cpu: 1
              count: 335
              high:  378
              batch: 63
  vm stats threshold: 36
    cpu: 2
              count: 300
              high:  378
              batch: 63
  vm stats threshold: 36
    cpu: 3
              count: 121
              high:  378
              batch: 63
  vm stats threshold: 36
  node_unreclaimable:  0
  start_pfn:           4096
Node 0, zone   Normal
  pages free     5754
        min      4615
        low      5768
        high     6921
        spanned  262144
        present  262144
        managed  236760
        protection: (0, 0, 0, 0, 0)
      nr_free_pages 5754
      nr_zone_inactive_anon 2366
      nr_zone_active_anon 75000
      nr_zone_inactive_file 49176
      nr_zone_active_file 57023
      nr_zone_unevictable 12
      nr_zone_write_pending 344
      nr_mlock     12
      nr_page_table_pages 5556
      nr_kernel_stack 7096
      nr_bounce    0
      nr_zspages   0
      nr_free_cma  0
      numa_hit     839519
      numa_miss    0
      numa_foreign 0
      numa_interleave 223408
      numa_local   839519
      numa_other   0
  pagesets
    cpu: 0
              count: 253
              high:  378
              batch: 63
  vm stats threshold: 24
    cpu: 1
              count: 202
              high:  378
              batch: 63
  vm stats threshold: 24
    cpu: 2
              count: 325
              high:  378
              batch: 63
  vm stats threshold: 24
    cpu: 3
              count: 291
              high:  378
              batch: 63
  vm stats threshold: 24
  node_unreclaimable:  0
  start_pfn:           1048576
Node 0, zone  Movable
  pages free     0
        min      0
        low      0
        high     0
        spanned  0
        present  0
        managed  0
        protection: (0, 0, 0, 0, 0)
Node 0, zone   Device
  pages free     0
        min      0
        low      0
        high     0
        spanned  0
        present  0
        managed  0
        protection: (0, 0, 0, 0, 0)
han@ubuntu:~$