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SubjectRe: [PATCH 09/10] mm: expose BDI statistics in sysfs.
On Fri, 20 Apr 2007 17:52:03 +0200 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Expose the per BDI stats in /sys/block/<dev>/queue/*
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> block/ll_rw_blk.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> Index: linux-2.6-mm/block/ll_rw_blk.c
> ===================================================================
> --- linux-2.6-mm.orig/block/ll_rw_blk.c
> +++ linux-2.6-mm/block/ll_rw_blk.c
> @@ -3976,6 +3976,15 @@ static ssize_t queue_max_hw_sectors_show
> return queue_var_show(max_hw_sectors_kb, (page));
> }
>
> +static ssize_t queue_nr_reclaimable_show(struct request_queue *q, char *page)
> +{
> + return sprintf(page, "%lld\n", bdi_stat(&q->backing_dev_info, BDI_RECLAIMABLE));
> +}

We try to present memory statistics to userspace in bytes or kbytes rather
than number-of-pages. Because page-size varies between architectures and
between .configs. Displaying number-of-pages is just inviting people to write
it-broke-when-i-moved-it-to-ia64 applications.

Plus kbytes is a bit more user-friendly, particularly when the user will
want to compare these numbers to /proc/meminfo, for example.

Using %llu might be more appropriate than %lld.

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