Re: [PATCH] vmscan: skip freeing memory from zones with lots free

Rik van Riel
2008-11-29T16:47:25Z

Andrew Morton wrote:

>> Index: linux-2.6.28-rc5/mm/vmscan.c
>> ===================================================================
>> --- linux-2.6.28-rc5.orig/mm/vmscan.c 2008-11-28 05:53:56.000000000 -0500
>> +++ linux-2.6.28-rc5/mm/vmscan.c 2008-11-28 06:05:29.000000000 -0500
>> @@ -1510,6 +1510,9 @@ static unsigned long shrink_zones(int pr
>> if (zone_is_all_unreclaimable(zone) &&
>> priority != DEF_PRIORITY)
>> continue; /* Let kswapd poll it */
>> + if (zone_watermark_ok(zone, sc->order,
>> + 4*zone->pages_high, high_zoneidx, 0))
>> + continue; /* Lots free already */
>> sc->all_unreclaimable = 0;
>> } else {
>> /*
>
> We already tried this, or something very similar in effect, I think...

Yes, we have a check just like this in balance_pgdat().

It's been there forever with no ill effect.

> commit 26e4931632352e3c95a61edac22d12ebb72038fe
> Author: akpm <akpm>
> Date: Sun Sep 8 19:21:55 2002 +0000
>
> [PATCH] refill the inactive list more quickly
>
> Fix a problem noticed by Ed Tomlinson: under shifting workloads the
> shrink_zone() logic will refill the inactive load too slowly.
>
> Bale out of the zone scan when we've reclaimed enough pages. Fixes a
> rarely-occurring problem wherein refill_inactive_zone() ends up
> shuffling 100,000 pages and generally goes silly.

This is not a bale out, this is a "skip zones that have way
too many free pages already".

Kswapd has been doing this for years already.

--
All rights reversed.