Re: [PATCH 03/12] Export unusable free space index via /proc/pagetypeinfo

[Mel Gorman <mel@csn.ul.ie>]

On Tue, Feb 16, 2010 at 04:03:29PM +0900, KOSAKI Motohiro wrote:
> > Unusuable free space index is a measure of external fragmentation that
> > takes the allocation size into account. 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.
> 
> Hmmm..
> /proc/pagetype have a machine unfriendly format. perhaps, some user have own ugly
> /proc/pagetype parser. It have a little risk to break userland ABI.
> 

It's very low risk. I doubt there are machine parsers of
/proc/pagetypeinfo because there are very few machine-orientated actions
that can be taken based on the information. It's more informational for
a user if they were investigating fragmentation problems.

> I have dumb question. Why can't we use another file?
> 

I could. What do you suggest?

> 
> > 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.
> 
> I think we can treat separately internal representaion and /proc displaing
> style. example, load-average have fixed point internal representaion. but
> /proc/loadavg hide it.
> 
> So, I personally like to keep this internal representation and change external
> representaion to 0.000-1.000 or 0.0%-100.0% range.
> 

I don't want to use a percentage for this value as there are two
indices, one of which can be expressed as a percentage and the other
not. I can represent it has a value between 0 and 1 if you prefer.

> 
> 
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > ---
> >  Documentation/filesystems/proc.txt |   10 ++++
> >  mm/vmstat.c                        |   99 ++++++++++++++++++++++++++++++++++++
> >  2 files changed, 109 insertions(+), 0 deletions(-)
> > 
> > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> > index 1829dfb..0968a81 100644
> > --- a/Documentation/filesystems/proc.txt
> > +++ b/Documentation/filesystems/proc.txt
> > @@ -614,6 +614,10 @@ Node    0, zone    DMA32, type      Movable    169    152    113     91     77
> >  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
> >  
> > +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
> > +
> >  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
> > @@ -629,6 +633,12 @@ 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.
> >  
> > +The unusable free space index measures how much of the available free
> > +memory cannot be used to satisfy an allocation of a given size and is a
> > +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.
> > +
> >  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 6051fba..d05d610 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -451,6 +451,104 @@ static int frag_show(struct seq_file *m, void *arg)
> >  	return 0;
> >  }
> >  
> > +
> > +struct contig_page_info {
> > +	unsigned long free_pages;
> > +	unsigned long free_blocks_total;
> > +	unsigned long free_blocks_suitable;
> > +};
> > +
> > +/*
> > + * Calculate the number of free pages in a zone, how many contiguous
> > + * pages are free and how many are large enough to satisfy an allocation of
> > + * the target size. Note that this function makes to attempt to estimate
> > + * how many suitable free blocks there *might* be if MOVABLE pages were
> > + * migrated. Calculating that is possible, but expensive and can be
> > + * figured out from userspace
> > + */
> > +static void fill_contig_page_info(struct zone *zone,
> > +				unsigned int suitable_order,
> > +				struct contig_page_info *info)
> > +{
> > +	unsigned int order;
> > +
> > +	info->free_pages = 0;
> > +	info->free_blocks_total = 0;
> > +	info->free_blocks_suitable = 0;
> > +
> > +	for (order = 0; order < MAX_ORDER; order++) {
> > +		unsigned long blocks;
> > +
> > +		/* Count number of free blocks */
> > +		blocks = zone->free_area[order].nr_free;
> > +		info->free_blocks_total += blocks;
> > +
> > +		/* Count free base pages */
> > +		info->free_pages += blocks << order;
> > +
> > +		/* Count the suitable free blocks */
> > +		if (order >= suitable_order)
> > +			info->free_blocks_suitable += blocks <<
> > +						(order - suitable_order);
> > +	}
> > +}
> > +
> > +/*
> > + * Return an index indicating how much of the available free memory is
> > + * unusable for an allocation of the requested size.
> > + */
> > +static int unusable_free_index(struct zone *zone,
> > +				unsigned int order,
> > +				struct contig_page_info *info)
> > +{
> > +	/* No free memory is interpreted as all free memory is unusable */
> > +	if (info->free_pages == 0)
> > +		return 1000;
> > +
> > +	/*
> > +	 * Index should be a value between 0 and 1. Return a value to 3
> > +	 * decimal places.
> > +	 *
> > +	 * 0 => no fragmentation
> > +	 * 1 => high fragmentation
> > +	 */
> 
> I leraned math by japanese. probably then I couldn't understand what mean
> "3 decimal places" awhile.
> Simply can't we write "Index should be a value between 0 and 1000"?
> 

I can do either that or make it really display between 0 and 1. I'd
prefer displaying between 0 and 1 myself.

> 
> > +	return ((info->free_pages - (info->free_blocks_suitable << order)) * 1000) / info->free_pages;
> > +
> > +}
> > +
> > +static void pagetypeinfo_showunusable_print(struct seq_file *m,
> > +					pg_data_t *pgdat, struct zone *zone)
> > +{
> > +	unsigned int order;
> > +
> > +	/* Alloc on stack as interrupts are disabled for zone walk */
> > +	struct contig_page_info info;
> > +
> > +	seq_printf(m, "Node %4d, zone %8s %19s",
> > +				pgdat->node_id,
> > +				zone->name, " ");
> > +	for (order = 0; order < MAX_ORDER; ++order) {
> > +		fill_contig_page_info(zone, order, &info);
> > +		seq_printf(m, "%6d ", unusable_free_index(zone, order, &info));
> > +	}
> > +
> > +	seq_putc(m, '\n');
> > +}
> > +
> > +/*
> > + * Display unusable free space index
> > + * XXX: Could be a lot more efficient, but it's not a critical path
> > + */
> > +static int pagetypeinfo_showunusable(struct seq_file *m, void *arg)
> > +{
> > +	pg_data_t *pgdat = (pg_data_t *)arg;
> > +
> > +	seq_printf(m, "\nUnusable free space index at order\n");
> > +	walk_zones_in_node(m, pgdat, pagetypeinfo_showunusable_print);
> > +
> > +	return 0;
> > +}
> > +
> >  static void pagetypeinfo_showfree_print(struct seq_file *m,
> >  					pg_data_t *pgdat, struct zone *zone)
> >  {
> > @@ -558,6 +656,7 @@ static int pagetypeinfo_show(struct seq_file *m, void *arg)
> >  	seq_printf(m, "Pages per block:  %lu\n", pageblock_nr_pages);
> >  	seq_putc(m, '\n');
> >  	pagetypeinfo_showfree(m, pgdat);
> > +	pagetypeinfo_showunusable(m, pgdat);
> >  	pagetypeinfo_showblockcount(m, pgdat);
> >  
> >  	return 0;
> > -- 
> > 1.6.5
> > 
> 
> 
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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