On Thu, Aug 19, 2010 at 01:57:27PM -0700, Michael Rubin wrote:
> The kernel already exposes the desired thresholds in /proc/sys/vm with
> dirty_background_ratio and background_ratio. Instead the kernel may
> alter the number requested without giving the user any indication that
> is the case.
You mean the 5% lower bound in global_dirty_limits()? Let's rip it :)
> 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_pages_dirty_threshold 409111
> nr_pages_dirty_background_threshold 818223
It's redundant to have _pages in the names. /proc/vmstat has the
tradition to use nr_dirty instead of nr_pages_dirty.
They do look like useful counters to export, especially when we do
dynamic dirty limits in future.
> Signed-off-by: Michael Rubin <mrubin@xxxxxxxxxx>
> ---
> include/linux/mmzone.h | 2 ++
> mm/vmstat.c | 8 ++++++++
> 2 files changed, 10 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index f160481..7c4a3bf 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -114,6 +114,8 @@ enum zone_stat_item {
> #endif
> NR_PAGES_ENTERED_WRITEBACK, /* number of times pages enter writeback */
> NR_FILE_PAGES_DIRTIED, /* number of times pages get dirtied */
> + NR_PAGES_DIRTY_THRESHOLD, /* writeback threshold */
> + NR_PAGES_DIRTY_BG_THRESHOLD,/* bg writeback threshold */
s/_PAGES//
> NR_VM_ZONE_STAT_ITEMS };
>
> /*
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index e177a40..8b5bc78 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -17,6 +17,7 @@
> #include <linux/vmstat.h>
> #include <linux/sched.h>
> #include <linux/math64.h>
> +#include <linux/writeback.h>
>
> #ifdef CONFIG_VM_EVENT_COUNTERS
> DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
> @@ -742,6 +743,8 @@ static const char * const vmstat_text[] = {
> #endif
> "nr_pages_entered_writeback",
> "nr_file_pages_dirtied",
> + "nr_pages_dirty_threshold",
> + "nr_pages_dirty_background_threshold",
s/_pages//
> #ifdef CONFIG_VM_EVENT_COUNTERS
> "pgpgin",
> @@ -901,6 +904,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
> #ifdef CONFIG_VM_EVENT_COUNTERS
> unsigned long *e;
> #endif
> + unsigned long dirty_thresh, dirty_bg_thresh;
> int i;
>
> if (*pos >= ARRAY_SIZE(vmstat_text))
> @@ -918,6 +922,10 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
> return ERR_PTR(-ENOMEM);
> for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> v[i] = global_page_state(i);
> +
> + get_dirty_limits(&dirty_thresh, &dirty_bg_thresh, NULL, NULL);
2.6.36-rc1 will need this:
global_dirty_limits(v + NR_DIRTY_THRESHOLD, v + NR_DIRTY_BG_THRESHOLD);
Thanks,
Fengguang
> + v[NR_PAGES_DIRTY_THRESHOLD] = dirty_thresh;
> + v[NR_PAGES_DIRTY_BG_THRESHOLD] = dirty_bg_thresh;
> #ifdef CONFIG_VM_EVENT_COUNTERS
> e = v + NR_VM_ZONE_STAT_ITEMS;
> all_vm_events(e);
> --
> 1.7.1
>
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