Re: reclaim the LRU lists full of dirty/writeback pages

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 14 Feb 2012 21:18:12 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

> 
> --- linux.orig/include/linux/backing-dev.h	2012-02-14 19:43:06.000000000 +0800
> +++ linux/include/linux/backing-dev.h	2012-02-14 19:49:26.000000000 +0800
> @@ -304,6 +304,8 @@ void clear_bdi_congested(struct backing_
>  void set_bdi_congested(struct backing_dev_info *bdi, int sync);
>  long congestion_wait(int sync, long timeout);
>  long wait_iff_congested(struct zone *zone, int sync, long timeout);
> +long reclaim_wait(long timeout);
> +void reclaim_rotated(void);
>  
>  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
>  {
> --- linux.orig/mm/backing-dev.c	2012-02-14 19:26:15.000000000 +0800
> +++ linux/mm/backing-dev.c	2012-02-14 20:09:45.000000000 +0800
> @@ -873,3 +873,38 @@ out:
>  	return ret;
>  }
>  EXPORT_SYMBOL(wait_iff_congested);
> +
> +static DECLARE_WAIT_QUEUE_HEAD(reclaim_wqh);
> +
> +/**
> + * reclaim_wait - wait for some pages being rotated to the LRU tail
> + * @timeout: timeout in jiffies
> + *
> + * Wait until @timeout, or when some (typically PG_reclaim under writeback)
> + * pages rotated to the LRU so that page reclaim can make progress.
> + */
> +long reclaim_wait(long timeout)
> +{
> +	long ret;
> +	unsigned long start = jiffies;
> +	DEFINE_WAIT(wait);
> +
> +	prepare_to_wait(&reclaim_wqh, &wait, TASK_KILLABLE);
> +	ret = io_schedule_timeout(timeout);
> +	finish_wait(&reclaim_wqh, &wait);
> +
> +	trace_writeback_reclaim_wait(jiffies_to_usecs(timeout),
> +				     jiffies_to_usecs(jiffies - start));
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(reclaim_wait);
> +
> +void reclaim_rotated()
> +{
> +	wait_queue_head_t *wqh = &reclaim_wqh;
> +
> +	if (waitqueue_active(wqh))
> +		wake_up(wqh);
> +}
> +

Thank you.

I like this approach. A nitpick is that this may wake up all waiters 
in the system when a memcg is rotated.

How about wait_event() + condition by bitmap (using per memcg unique IDs.) ?


Thanks,
-Kame

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