Hi,
On Thu, Jan 12, 2012 at 01:47:02PM +0800, Huang Shijie wrote:
In the real tests, there are maybe many times the cc->nr_migratepages is zero,
but isolate_migratepages() returns ISOLATE_SUCCESS.
Memory in our mx6q board:
2G memory, 8192 pages per page block
We use the following command to test in two types system loads:
#echo 1> /proc/sys/vm/compact_memory
Test Result:
[1] little load(login in the ubuntu):
all the scanned pageblocks : 79
pageblocks which get no pages : 46
The ratio of `get no pages` pageblock is 58.2%.
[2] heavy load(start thunderbird, firefox, ..etc):
all the scanned pageblocks : 89
pageblocks which get no pages : 36
The ratio of `get no pages` pageblock is 40.4%.
In order to get better performance, we should check the number of the
really isolated pages. And do the optimazition for this case.
Also fix the confused comments(from Mel Gorman).
Tested this patch in MX6Q board.
Signed-off-by: Huang Shijie<b32955@xxxxxxxxxxxxx>
Acked-by: Mel Gorman<mgorman@xxxxxxx>
---
mm/compaction.c | 28 ++++++++++++++++------------
1 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index f4f514d..41d1b72a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -246,8 +246,8 @@ static bool too_many_isolated(struct zone *zone)
/* possible outcome of isolate_migratepages */
typedef enum {
ISOLATE_ABORT, /* Abort compaction now */
- ISOLATE_NONE, /* No pages isolated, continue scanning */
- ISOLATE_SUCCESS, /* Pages isolated, migrate */
+ ISOLATE_NONE, /* No pages scanned, consider next pageblock*/
+ ISOLATE_SUCCESS, /* Pages scanned and maybe isolated, migrate */
} isolate_migrate_t;
Hmm, I don't like this change.
ISOLATE_NONE mean "we don't isolate any page at all"
ISOLATE_SUCCESS mean "We isolaetssome pages"
It's very clear but you are changing semantic slighly.
I think Mel Gorman's new explain is more proper.
How about this?
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -376,7 +376,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
- return ISOLATE_SUCCESS;
+ return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
}
/*
@@ -542,6 +542,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
unsigned long nr_migrate, nr_remaining;
int err;
+ count_vm_event(COMPACTBLOCKS);
not right.
the isolate_migratepage may returns ISOLATE_NONE. We should not account
this case.
Best Regards
Huang Shijie
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