netdev - Re: [PATCH 13/13] mm: Account for the number of times direct reclaimers get throttled

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Date:	Tue, 26 Apr 2011 22:35:10 +1000
From:	NeilBrown <neilb@...e.de>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 13/13] mm: Account for the number of times direct
 reclaimers get throttled

On Tue, 26 Apr 2011 08:36:54 +0100 Mel Gorman <mgorman@...e.de> wrote:

> Under significant pressure when writing back to network-backed storage,
> direct reclaimers may get throttled. This is expected to be a
> short-lived event and the processes get woken up again but processes do
> get stalled. This patch counts how many times such stalling occurs. It's
> up to the administrator whether to reduce these stalls by increasing
> min_free_kbytes.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  include/linux/vm_event_item.h |    1 +
>  mm/vmscan.c                   |    1 +
>  mm/vmstat.c                   |    1 +
>  3 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 03b90cdc..652e5f3 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -29,6 +29,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  		FOR_ALL_ZONES(PGSTEAL),
>  		FOR_ALL_ZONES(PGSCAN_KSWAPD),
>  		FOR_ALL_ZONES(PGSCAN_DIRECT),
> +		PGSCAN_DIRECT_THROTTLE,
>  #ifdef CONFIG_NUMA
>  		PGSCAN_ZONE_RECLAIM_FAILED,
>  #endif
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8b6da2b..e88138b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2154,6 +2154,7 @@ static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
>  		goto out;
>  
>  	/* Throttle */
> +	count_vm_event(PGSCAN_DIRECT_THROTTLE);
>  	do {
>  		schedule();
>  		finish_wait(&zone->zone_pgdat->pfmemalloc_wait, &wait);
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index a2b7344..5725387 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -911,6 +911,7 @@ const char * const vmstat_text[] = {
>  	TEXTS_FOR_ZONES("pgsteal")
>  	TEXTS_FOR_ZONES("pgscan_kswapd")
>  	TEXTS_FOR_ZONES("pgscan_direct")
> +	"pgscan_direct_throttle",
>  
>  #ifdef CONFIG_NUMA
>  	"zone_reclaim_failed",

I like this approach.  Make the information available, but don't make a fuss
about it.

Actually, I like the whole series - I'm really having to dig deep to find
anything to complain about :-)

Feel free to put
   Reviewed-by: NeilBrown <neilb@...e.de>
against anything that I haven't commented on.

Thanks,
NeilBrown
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