Re: [PATCH 01/12] mm: Document /proc/pagetypeinfo

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> The memory compaction patches add details to pagetypeinfo that are not
> obvious and need to be documented. In preparation for this, document
> what is already in /proc/pagetypeinfo.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>

Looks nicer.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

> ---
>  Documentation/filesystems/proc.txt |   45 +++++++++++++++++++++++++++++++++++-
>  1 files changed, 44 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index 0d07513..1829dfb 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -430,6 +430,7 @@ 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)
> @@ -584,7 +585,7 @@ 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.
> @@ -594,6 +595,48 @@ 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:
> -- 
> 1.6.5
>