mm, pcp: reduce detecting time of consecutive high order page freeing

In current PCP auto-tuning design, if the number of pages allocated is
much more than that of pages freed on a CPU, the PCP high may become the
maximal value even if the allocating/freeing depth is small, for example,
in the sender of network workloads.  If a CPU was used as sender
originally, then it is used as receiver after context switching, we need
to fill the whole PCP with maximal high before triggering PCP draining for
consecutive high order freeing.  This will hurt the performance of some
network workloads.

To solve the issue, in this patch, we will track the consecutive page
freeing with a counter in stead of relying on PCP draining.  So, we can
detect consecutive page freeing much earlier.

On a 2-socket Intel server with 128 logical CPU, we tested
SCTP_STREAM_MANY test case of netperf test suite with 64-pair processes. 
With the patch, the network bandwidth improves 5.0%.  This restores the
performance drop caused by PCP auto-tuning.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Sudeep Holla <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b92ab001e146..3c25226beeed 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -698,10 +698,10 @@ struct per_cpu_pages {
 	int batch;		/* chunk size for buddy add/remove */
 	u8 flags;		/* protected by pcp->lock */
 	u8 alloc_factor;	/* batch scaling factor during allocate */
-	u8 free_factor;		/* batch scaling factor during free */
 #ifdef CONFIG_NUMA
 	u8 expire;		/* When 0, remote pagesets are drained */
 #endif
+	short free_count;	/* consecutive free count */
 
 	/* Lists of pages, one per migrate type stored on the pcp-lists */
 	struct list_head lists[NR_PCP_LISTS];