On Sun, 19 Jun 2011 23:01:11 +0800
Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> The start of a heavy weight application (ie. KVM) may instantly knock
> down determine_dirtyable_memory() and hence the global/bdi dirty
> thresholds.
>
> So introduce global_dirty_limit for tracking the global dirty threshold
> with policies
>
> - follow downwards slowly
> - follow up in one shot
>
> global_dirty_limit can effectively mask out the impact of sudden drop of
> dirtyable memory. It will be used in the next patch for two new type of
> dirty limits.
>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> include/linux/writeback.h | 2 +
> mm/page-writeback.c | 41 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 43 insertions(+)
>
> --- linux-next.orig/include/linux/writeback.h 2011-06-19 22:56:18.000000000 +0800
> +++ linux-next/include/linux/writeback.h 2011-06-19 22:59:29.000000000 +0800
> @@ -88,6 +88,8 @@ static inline void laptop_sync_completio
> #endif
> void throttle_vm_writeout(gfp_t gfp_mask);
>
> +extern unsigned long global_dirty_limit;
> +
> /* These are exported to sysctl. */
> extern int dirty_background_ratio;
> extern unsigned long dirty_background_bytes;
> --- linux-next.orig/mm/page-writeback.c 2011-06-19 22:56:18.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2011-06-19 22:59:29.000000000 +0800
> @@ -116,6 +116,7 @@ EXPORT_SYMBOL(laptop_mode);
>
> /* End of sysctl-exported parameters */
>
> +unsigned long global_dirty_limit;
>
> /*
> * Scale the writeback cache size proportional to the relative writeout speeds.
> @@ -510,6 +511,43 @@ static void bdi_update_write_bandwidth(s
> bdi->avg_write_bandwidth = avg;
> }
>
> +static void update_dirty_limit(unsigned long thresh,
> + unsigned long dirty)
> +{
> + unsigned long limit = global_dirty_limit;
> +
> + if (limit < thresh) {
> + limit = thresh;
> + goto update;
> + }
> +
> + if (limit > thresh &&
> + limit > dirty) {
> + limit -= (limit - max(thresh, dirty)) >> 5;
> + goto update;
> + }
> + return;
> +update:
> + global_dirty_limit = limit;
> +}
Are
you
using
a
30
column
monitor
over
there?
This function is just crazy. It compares various things, applies
limits, churns them all together with magic constants and does it all
in a refreshingly documentation-free manner.
How the heck is anyone supposed to understand what you were thinking
when you typed it in?
Please, write for an audience.
> +static void global_update_bandwidth(unsigned long thresh,
> + unsigned long dirty,
> + unsigned long now)
> +{
> + static DEFINE_SPINLOCK(dirty_lock);
> +
> + if (now - default_backing_dev_info.bw_time_stamp < MAX_PAUSE)
> + return;
> +
> + spin_lock(&dirty_lock);
> + if (now - default_backing_dev_info.bw_time_stamp >= MAX_PAUSE) {
> + update_dirty_limit(thresh, dirty);
> + default_backing_dev_info.bw_time_stamp = now;
> + }
> + spin_unlock(&dirty_lock);
> +}
Why is it playing with default_backing_dev_info? That's only there to
support filesystems which were too old-and-slack to implement
backing-devs properly and it really shouldn't exist at all.
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