How to Interpret Linux /proc Memory Files for Troubleshooting

/proc/zoneinfo

# cat /proc/zoneinfo
Node 0, zone      DMA
 pages  free 808251
         min 1912
         low 2390
         high 2868
         scanned 0
         spanned 1015296
         present 1007616
         managed 917418
 nr_free_pages 808251
 nr_alloc_batch 69
 nr_inactive_anon 1878
 nr_active_anon 35777
 nr_inactive_file 36299
 nr_active_file 12876
 nr_unevictable 0
 nr_mlock 0
 nr_anon_pages 35598
 nr_mapped 29010
 nr_file_pages 51233
 nr_dirty 0
 nr_writeback 0
 nr_slab_reclaimable 8099
 nr_slab_unreclaimable 5837
 nr_page_table_pages 1105
 nr_kernel_stack 326
 nr_shmem 2059
 nr_dirtied 3391
 nr_written 3384
 nr_pages_scanned 0
 workingset_refault 0
 workingset_activate 0
 workingset_nodereclaim 0
 nr_anon_transparent_hugepages 0
 nr_free_cma 0
 protection: (0, 0, 0)
 pagesets
  cpu: 0 count: 33 high: 186 batch: 31 vm stats threshold: 36
  cpu: 1 count: 58 high: 186 batch: 31 vm stats threshold: 36
  cpu: 2 count: 93 high: 186 batch: 31 vm stats threshold: 36
  cpu: 3 count: 139 high: 186 batch: 31 vm stats threshold: 36
  cpu: 4 count: 185 high: 186 batch: 31 vm stats threshold: 36
 all_unreclaimable: 0
 start_pfn: 512
 inactive_ratio: 5

Important fields: pages free – available free pages. min / low / high – watermarks that trigger reclamation. present – total physical pages present. managed – pages managed by the kernel. nr_free_pages – same as pages free. nr_inactive_anon / nr_active_anon – inactive/active anonymous pages. nr_inactive_file / nr_active_file – inactive/active file‑backed pages. nr_slab_reclaimable / nr_slab_unreclaimable – reclaimable vs. unreclaimable slab memory. nr_shmem – shared memory pages. nr_dirty / nr_written – dirty and written pages.

Typical signs of trouble: pages free close to 0 → high memory pressure or leak.

Increasing nr_slab_unreclaimable → possible slab leak.

Very high nr_shmem → shared memory consuming excessive RAM, OOM risk.

Persistently high nr_dirty → I/O pressure.

Abnormal nr_file_pages / nr_anon_pages ratio → investigate file cache vs. private memory usage.

/proc/pagetypeinfo

# cat /proc/pagetypeinfo
Page block order: 9
Pages per block: 512
Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone DMA, type Unmovable 18 10 2 0 1 1 1 0 1 1 1 0
Node 0, zone DMA, type Movable 0 1 0 0 0 0 1 1 1 0 0 0 832
Node 0, zone DMA, type Reclaimable 1 0 1 0 1 1 1 0 1 1 1 0
Number of blocks type Unmovable  Movable  Reclaimable  HighAtomic
Node 0, zone DMA 26 1924 18 0

Each block contains 512 pages (2⁹). The columns correspond to order 0 – 10 free block counts for each migration type. Unmovable – pages that cannot be moved. Movable – pages that can be relocated. Reclaimable – pages that the kernel can reclaim. HighAtomic – high‑atomic allocation pages.

If high‑order free blocks are scarce for Unmovable, the system suffers from memory fragmentation.

/proc/meminfo

# cat /proc/meminfo
MemTotal:        3669672 kB
MemFree:         3233664 kB
MemAvailable:    3432196 kB
Buffers:            10192 kB
Cached:            194796 kB
SwapCached:            0 kB
Active:            194344 kB
Inactive:          152704 kB
Active(anon):      142788 kB
Inactive(anon):      7508 kB
Active(file):        51556 kB
Inactive(file):     145196 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:            0 kB
SwapFree:             0 kB
Dirty:                 28 kB
Writeback:              0 kB
AnonPages:        142160 kB
Mapped:            116020 kB
Shmem:               8232 kB
Slab:               55688 kB
SReclaimable:       32372 kB
SUnreclaim:         23316 kB
KernelStack:          5216 kB
PageTables:           4400 kB
CommitLimit:     1834836 kB
Committed_AS:   1375504 kB
VmallocTotal: 258867136 kB
VmallocUsed:           0 kB
HugePages_Total:       0
HugePages_Free:        0
Hugepagesize:       2048 kB

Key fields used by free -m: MemTotal – total physical memory. MemFree – completely unused memory. MemAvailable – estimate of memory available for new processes (more accurate than MemFree). Buffers – block device buffers. Cached – file cache, reclaimable under pressure. SwapCached – pages swapped out then read back but not yet freed. Active / Inactive – active vs. inactive memory. Slab – total kernel slab memory (SReclaimable + SUnreclaim). CommitLimit – maximum memory the system can commit. Committed_AS – memory already committed; approaching CommitLimit raises OOM risk.

Typical checks:

Low MemFree and MemAvailable together indicate memory pressure.

Non‑zero SwapCached suggests insufficient RAM and frequent swapping.

Large Slab, especially a high SUnreclaim, may point to kernel object leaks. Committed_AS close to CommitLimit signals imminent OOM.

/proc/buddyinfo

# cat /proc/buddyinfo
Node 0, zone      DMA      28      9      9      6      1      3      1      1      2      2    787

Columns correspond to order 0 – 10 free block counts. A pattern of large numbers in early columns and small numbers later indicates serious fragmentation.

/proc/slabinfo

# cat /proc/slabinfo
slabinfo - version: 2.1
# name           <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables ...
 dentry          36017  36198   216   18   1 : tunables   0   0   0 : slabdata   2011   2011      0
 inode_cache     22152  22152   680   24   4 : tunables   0   0   0 : slabdata    923    923      0
 ext4_inode_cache 3425   3425   1296  25   8 : tunables   0   0   0 : slabdata    137    137      0
 ...

Each line shows: cache name, active objects, total objects, object size, objects per slab, pages per slab. When diagnosing slab leaks, monitor active_objs. If it keeps growing while the system is idle, the corresponding cache (e.g., dentry, inode_cache, kmalloc-*) is likely leaking.

/proc/vmallocinfo

0xffffff8008000000-0xffffff8008011000   69632 of_iomap+0x48/0x5c phys=fee00000 ioremap
0xffffff8008018000-0xffffff800801a000    8192 bpf_prog_alloc+0x48/0xb4 pages=1 vmalloc
0xffffffbdbff72000-0xffffffbdbfff0000  516096 pcpu_get_vm_areas+0x0/0x500 vmalloc

Format:

start‑end size allocation‑function physical‑address (if ioremap) allocation‑type

. Use this file to identify components that consume virtual memory via vmalloc or ioremap.

/proc/vmstat

nr_free_pages 807632
nr_alloc_batch 478
nr_inactive_anon 1876
nr_active_anon 35696
...
pgpgin 212188
pgpgout 17004
pswpin 0
pswpout 0
pgmajfault 1418
...

Global memory event counters. Relevant indicators: pswpin / pswpout non‑zero → physical memory insufficient, heavy swapping. pgmajfault high → many major page faults, sign of memory pressure. allocstall non‑zero → allocation stalls, indicating high pressure.

/proc/self/statm

927 111 95 7 0 108 0

Fields (pages, usually 4 KB):

1 – total virtual pages.

2 – resident set size (RSS).

3 – shared pages (shared libraries, etc.).

4 – code segment.

5 – data/heap.

6 – stack.

7 – swapped out pages.

/proc/self/maps

5578fe8000-5578fef000 r-xp 00000000 b3:07 181803 /bin/cat
558ad0e000-558ad2f000 rw-p 00000000 00:00 0 [heap]
7f9e147000-7f9e286000 r-xp 00000000 b3:07 91231 /lib/aarch64-linux-gnu/libc-2.27.so
7fee78b000-7fee7ac000 rw-p 00000000 00:00 0 [stack]
...

Each line format: start‑end permissions offset device:inode path. Permissions: r=read, w=write, x=execute, p=private, s=shared. When debugging memory layout, look for unusually large mappings or excessive anonymous mappings.

/proc/sys/vm

Adjustable kernel memory‑management parameters (common ones): dirty_ratio – percentage of memory that, when dirty pages exceed it, triggers write‑back. dirty_background_ratio – percentage at which background threads start flushing dirty pages. drop_caches – write 1/2/3 to free page cache / dentry cache / inode cache. min_free_kbytes – minimum amount of free memory the kernel tries to keep. swappiness – preference for swapping (0–100). overcommit_memory – 0=heuristic, 1=always allow, 2=prevent overallocation. vfs_cache_pressure – aggressiveness of VFS cache reclamation (higher = more aggressive).

/proc/swaps

Filename                Type      Size    Used   Priority
/dev/sda2               partition 8388604 0      -1

Check the Used column; values close to Size indicate severe physical memory pressure.

Reference: https://www.cnblogs.com/arnoldlu/p/8568330.html