On Fri, 2010-02-12 at 12:00 +0000, Mel Gorman wrote: > Fragmentation index is a value that makes sense when an allocation of a > given size would fail. The index indicates whether an allocation failure is > due to a lack of memory (values towards 0) or due to external fragmentation > (value towards 1). For the most part, the huge page size will be the size > of interest but not necessarily so it is exported on a per-order and per-zone > basis via /proc/pagetypeinfo. > > The index is normally calculated as a value between 0 and 1 which is > obviously unsuitable within the kernel. Instead, the first three decimal > places are used as a value between 0 and 1000 for an integer approximation. > > Signed-off-by: Mel Gorman <mel@xxxxxxxxx> Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > --- > Documentation/filesystems/proc.txt | 11 ++++++ > mm/vmstat.c | 63 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 74 insertions(+), 0 deletions(-) > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index 0968a81..06bf53c 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -618,6 +618,10 @@ Unusable free space index at order > Node 0, zone DMA 0 0 0 2 6 18 34 67 99 227 485 > Node 0, zone DMA32 0 0 1 2 4 7 10 17 23 31 34 > > +Fragmentation index at order > +Node 0, zone DMA -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 > +Node 0, zone DMA32 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 > + > 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 > @@ -639,6 +643,13 @@ value between 0 and 1000. The higher the value, the more of free memory is > unusable and by implication, the worse the external fragmentation is. The > percentage of unusable free memory can be found by dividing this value by 10. > > +The fragmentation index, is only meaningful if an allocation would fail and > +indicates what the failure is due to. A value of -1 such as in the example > +states that the allocation would succeed. If it would fail, the value is > +between 0 and 1000. A value tending towards 0 implies the allocation failed > +due to a lack of memory. A value tending towards 1000 implies it failed > +due to external fragmentation. > + > 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 > diff --git a/mm/vmstat.c b/mm/vmstat.c > index d05d610..e2d0cc1 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -494,6 +494,35 @@ static void fill_contig_page_info(struct zone *zone, > } > > /* > + * A fragmentation index only makes sense if an allocation of a requested > + * size would fail. If that is true, the fragmentation index indicates > + * whether external fragmentation or a lack of memory was the problem. > + * The value can be used to determine if page reclaim or compaction > + * should be used > + */ > +int fragmentation_index(struct zone *zone, Like previous [3/12], why do you remain "zone" argument? If you will use it in future, I don't care. It's just trivial. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>