Entries in /proc/meminfo

Question

I can make sense of most of the information contained in /proc/meminfo like total memory, buffers, cache etc. Could you tell me what do the less obvious ones like the ones listed below mean?

• AnonPages
• Mapped
• Slab
• NFS_Unstable
• Bounce
• VmallocTotal
• VmallocUsed
• VmallocChunk

If anyone is wondering, I am talking about the output of the linux command cat /proc/meminfo

Answer 1

The canonical source of this information is /usr/src/linux/Documentation/filesystems/proc.txt. Specifically,

   AnonPages: Non-file backed pages mapped into userspace page tables
      Mapped: files which have been mmaped, such as libraries
        Slab: in-kernel data structures cache
NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
        storage
      Bounce: Memory used for block device "bounce buffers"
VmallocTotal: total size of vmalloc memory area
 VmallocUsed: amount of vmalloc area which is used
VmallocChunk: largest contigious block of vmalloc area which is free

Answer 2

My understanding is as follows.
And I agree these numbers are hard to understand and showing inconsistent values.

• MemTotal

  = MemFree + Active + Inactive + Slab + PageTables + VmallocUsed + X
  (X : alloc_pages() (get_free_pages(), etc))
  

  But recent kernel's vmallocused value could be wrong. This is because it counts VM_xxx regions like VM_IOREMAP, VM_MAP,... other than VM_ALLOC area.

  VM_IOREMAP region can be mapping memory which can be outside of kernel's memory management, so the formula above can be not precise, or completely wrong.

  You can either do:

  • Check /proc/vmallocinfo to sort out all the entries and filter by yourself,
  • Modify fs/proc/mmu.c: get_vmalloc_info() to count regions only when if(vma->flags & VM_ALLOC)

• Active + Inactive

   = Buffers + Cached + SwapCached + AnonPages
  

• AnonPages

   = /proc/*/task/*/smaps anonymous area all sum
   (anonymous: no name|[heap]|/dev/zero|/dev/shm/*|[stack])
  

  Although I haven't been able to match these numbers. See here and help me if you have any clue.

• Total PageCache

   = Buffers + Cached + SwapCached
  

• Slab

   = SReclaimable + SUnreclaim
  

Answer 3

From RedHat

VMallocTotal — The total amount of memory, in kilobytes, of total allocated virtual address space. VMallocUsed — The total amount of memory, in kilobytes, of used virtual address space. VMallocChunk — The largest contiguous block of memory, in kilobytes, of available virtual address space.