On 08/16/2016 08:41 AM, Joonsoo Kim wrote:
>> free pages for probability of compaction success, so I don't think
>> it's worth complicating the compact_gap() formula.
>
> I agree that it's not worth complicating the compact_gap() formula but
> it would be better to fix the comment?
OK, Andrew can you add this -fix?
Thanks.
----8<----
>From cad7fb3a61c24feb53e8754248d67715b8ce0c3e Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@xxxxxxx>
Date: Thu, 18 Aug 2016 14:11:28 +0200
Subject: [PATCH] mm, compaction: create compact_gap wrapper-fix
Clarify the comment of compact_gap() wrt COMPACT_CLUSTER_MAX, per Joonsoo.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
include/linux/compaction.h | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index e7f0d34a90fe..585d55cb0dc0 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -67,9 +67,16 @@ static inline unsigned long compact_gap(unsigned int order)
{
/*
* Although all the isolations for migration are temporary, compaction
- * may have up to 1 << order pages on its list and then try to split
- * an (order - 1) free page. At that point, a gap of 1 << order might
- * not be enough, so it's safer to require twice that amount.
+ * free scanner may have up to 1 << order pages on its list and then
+ * try to split an (order - 1) free page. At that point, a gap of
+ * 1 << order might not be enough, so it's safer to require twice that
+ * amount. Note that the number of pages on the list is also
+ * effectively limited by COMPACT_CLUSTER_MAX, as that's the maximum
+ * that the migrate scanner can have isolated on migrate list, and free
+ * scanner is only invoked when the number of isolated free pages is
+ * lower than that. But it's not worth to complicate the formula here
+ * as a bigger gap for higher orders than strictly necessary can also
+ * improve chances of compaction success.
*/
return 2UL << order;
}
--
2.9.2
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>