On Fri, Aug 20, 2010 at 05:31:29PM +0800, Michael Rubin wrote:
quoted text
> The kernel already exposes the user desired thresholds in /proc/sys/vm
> with dirty_background_ratio and background_ratio. But the kernel may
> alter the number requested without giving the user any indication that
> is the case.
> 
> Knowing the actual ratios the kernel is honoring can help app developers
> understand how their buffered IO will be sent to the disk.
> 
> 	$ grep threshold /proc/vmstat
> 	nr_dirty_threshold 409111
> 	nr_dirty_background_threshold 818223
> 
> Signed-off-by: Michael Rubin <mrubin@google.com>
> ---
>  include/linux/mmzone.h |    3 +++
>  mm/vmstat.c            |    5 +++++
>  2 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index fe4e6dd..c2243d0 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -106,6 +106,9 @@ enum zone_stat_item {
>  	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
>  	NR_FILE_PAGES_DIRTIED,	/* number of times pages get dirtied */
>  	NR_PAGES_ENTERED_WRITEBACK, /* number of times pages enter writeback */
> +	NR_DIRTY_THRESHOLD,	/* writeback threshold */
> +	NR_DIRTY_BG_THRESHOLD,	/* bg writeback threshold */

This may cost cacheline.

Thanks,
Fengguang
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