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Date: Tue, 16 Feb 2010 16:03:29 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Mel Gorman <mel@....ul.ie>
Cc: kosaki.motohiro@...fujitsu.com,
Andrea Arcangeli <aarcange@...hat.com>,
Christoph Lameter <cl@...ux-foundation.org>,
Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
David Rientjes <rientjes@...gle.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 03/12] Export unusable free space index via /proc/pagetypeinfo
> 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.
I have dumb question. Why can't we use another file?
> 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.
> Signed-off-by: Mel Gorman <mel@....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"?
> + 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
>
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