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Commit a1b57ac0 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm: document /proc/pagetypeinfo 



Add documentation for /proc/pagetypeinfo.

Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Reviewed-by: default avatarChristoph Lameter <cl@linux-foundation.org>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 72f0ba02

Documentation/filesystems/proc.txt

+44 −1
Original line number Diff line number Diff line
@@ -438,6 +438,7 @@ Table 1-5: Kernel info in /proc 
 modules     List of loaded modules                            

 mounts      Mounted filesystems                               

 net         Networking info (see text)                        

 pagetypeinfo Additional page allocator information (see text)  (2.5)

 partitions  Table of partitions known to the system           

 pci	     Deprecated info of PCI bus (new way -> /proc/bus/pci/,

             decoupled by lspci					(2.4)
@@ -592,7 +593,7 @@ Node 0, zone DMA 0 4 5 4 4 3 ... 
Node 0, zone   Normal      1      0      0      1    101      8 ...

Node 0, zone  HighMem      2      0      0      1      1      0 ...



Memory fragmentation is a problem under some workloads, and buddyinfo is a 

External fragmentation is a problem under some workloads, and buddyinfo is a

useful tool for helping diagnose these problems.  Buddyinfo will give you a 

clue as to how big an area you can safely allocate, or why a previous

allocation failed.
@@ -602,6 +603,48 @@ available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 

available in ZONE_NORMAL, etc... 



More information relevant to external fragmentation can be found in

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      0      0      0      1      1      1      1      1      1      1      0

Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0

Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2

Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0

Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0

Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9

Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0

Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452

Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0

Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0



Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate

Node 0, zone      DMA            2            0            5            1            0

Node 0, zone    DMA32           41            6          967            2            0



Fragmentation avoidance in the kernel works by grouping pages of different

migrate types into the same contiguous regions of memory called page blocks.

A page block is typically the size of the default hugepage size e.g. 2MB on

X86-64. By keeping pages grouped based on their ability to move, the kernel

can reclaim pages within a page block to satisfy a high-order allocation.



The pagetypinfo begins with information on the size of a page block. It

then gives the same type of information as buddyinfo except broken down

by migrate-type and finishes with details on how many page blocks of each

type exist.



If min_free_kbytes has been tuned correctly (recommendations made by hugeadm

from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can

make an estimate of the likely number of huge pages that can be allocated

at a given point in time. All the "Movable" blocks should be allocatable

unless memory has been mlock()'d. Some of the Reclaimable blocks should

also be allocatable although a lot of filesystem metadata may have to be

reclaimed to achieve this.



..............................................................................



meminfo: