On 05/23/2016 05:20 AM, Chen Feng wrote:
There are two paths calling this function.
For direct compact, there is no need to check the zone watermark here.
For kswapd wakeup kcompactd, since there is a reclaim before this.
It makes sense to do compact even the watermark is ok at this time.
Hi,
I'm just working on v2 of the series [1] and some patches planned for v2 are
trying to simplify the watermark checks around compaction. The check you are
removing looked like simple and obvious one, so I didn't change it. But I'll
think more about your patch, e.g. if there are some corner cases. See for
example the fragindex check:
* index of -1000 would imply allocations might succeed depending on
* watermarks, but we already failed the high-order watermark check
After your patch, there is no more high-order watermark check, so the assumption
here is gone.
Also the comment above __compaction_suitable() should be updated too.
[1] http://lkml.kernel.org/r/<1462865763-22084-1-git-send-email-vbabka@xxxxxxx>
Signed-off-by: Chen Feng <puck.chen@xxxxxxxxxxxxx>
---
mm/compaction.c | 7 -------
1 file changed, 7 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 8fa2540..cb322df 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1260,13 +1260,6 @@ static unsigned long __compaction_suitable(struct zone *zone, int order,
return COMPACT_CONTINUE;
watermark = low_wmark_pages(zone);
- /*
- * If watermarks for high-order allocation are already met, there
- * should be no need for compaction at all.
- */
- if (zone_watermark_ok(zone, order, watermark, classzone_idx,
- alloc_flags))
- return COMPACT_PARTIAL;
/*
* Watermarks for order-0 must be met for compaction. Note the 2UL.
--
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