Re: [PATCH 03/10] mm: vmscan: Flatten kswapd priority loop
From: Mel Gorman
Date: Tue Mar 19 2013 - 06:14:35 EST
On Tue, Mar 19, 2013 at 11:08:23AM +0800, Simon Jeons wrote:
> Hi Mel,
> On 03/17/2013 09:04 PM, Mel Gorman wrote:
> >kswapd stops raising the scanning priority when at least SWAP_CLUSTER_MAX
> >pages have been reclaimed or the pgdat is considered balanced. It then
> >rechecks if it needs to restart at DEF_PRIORITY and whether high-order
> >reclaim needs to be reset. This is not wrong per-se but it is confusing
> per-se is short for what?
It means "in self" or "as such".
> >to follow and forcing kswapd to stay at DEF_PRIORITY may require several
> >restarts before it has scanned enough pages to meet the high watermark even
> >at 100% efficiency. This patch irons out the logic a bit by controlling
> >when priority is raised and removing the "goto loop_again".
> >This patch has kswapd raise the scanning priority until it is scanningmm: vmscan: Flatten kswapd priority loop
> >enough pages that it could meet the high watermark in one shrink of the
> >LRU lists if it is able to reclaim at 100% efficiency. It will not raise
> Which kind of reclaim can be treated as 100% efficiency?
100% efficiency is where every page scanned can be reclaimed immediately.
> > /*
> >- * We do this so kswapd doesn't build up large priorities for
> >- * example when it is freeing in parallel with allocators. It
> >- * matches the direct reclaim path behaviour in terms of impact
> >- * on zone->*_priority.
> >+ * Fragmentation may mean that the system cannot be rebalanced
> >+ * for high-order allocations in all zones. If twice the
> >+ * allocation size has been reclaimed and the zones are still
> >+ * not balanced then recheck the watermarks at order-0 to
> >+ * prevent kswapd reclaiming excessively. Assume that a
> >+ * process requested a high-order can direct reclaim/compact.
> > */
> >- if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
> >- break;
> >- } while (--sc.priority >= 0);
> >+ if (order && sc.nr_reclaimed >= 2UL << order)
> >+ order = sc.order = 0;
> If order == 0 is meet, should we do defrag for it?
Compaction is unnecessary for order-0.
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