Messages in this thread | | | Date | Tue, 9 Jun 2009 22:23:01 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA |
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On Mon, 8 Jun 2009 16:11:51 +0100 Mel Gorman <mel@csn.ul.ie> wrote:
> On Mon, Jun 08, 2009 at 10:55:55AM -0400, Christoph Lameter wrote: > > On Mon, 8 Jun 2009, Mel Gorman wrote: > > > > > > The tmpfs pages are unreclaimable and therefore should not be on the anon > > > > lru. > > > > > > > > > > tmpfs pages can be swap-backed so can be reclaimable. Regardless of what > > > list they are on, we still need to know how many of them there are if > > > this patch is to be avoided. > > > > If they are reclaimable then why does it matter? They can be pushed out if > > you configure zone reclaim to be that aggressive. > > > > Because they are reclaimable by kswapd or normal direct reclaim but *not* > reclaimable by zone_reclaim() if the zone_reclaim_mode is not configured > appropriately.
Ah. (zone_reclaim_mode & RECLAIM_SWAP) == 0. That was important info.
Couldn't the lack of RECLAIM_WRITE cause a similar problem?
> I briefly considered setting zone_reclaim_mode to 7 instead of > 1 by default for large NUMA distances but that has other serious consequences > such as paging in preference to going off-node as a default out-of-box > behaviour.
Maybe we should consider that a bit harder. At what stage does zone_reclaim decide to give up and try a different node? Perhaps it's presently too reluctant to do that?
> The point of the patch is that the heuristics that avoid the scan are not > perfect. In the event they are wrong and a useless scan occurs, the response > of the kernel after a useless scan should not be to uselessly scan a load > more times around the LRU lists making no progress.
It would be sad to bring back a jiffies-based thing into page reclaim. Wall time has little correlation with the rate of page allocation and reclaim activity.
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