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Subject[PATCH 6/6] mm: kswapd: Use the classzone idx that kswapd was using for sleeping_prematurely()
Date
When kswapd is woken up for a high-order allocation, it takes account of
the highest usable zone by the caller (the classzone idx). During
allocation, this index is used to select the lowmem_reserve[] that
should be applied to the watermark calculation in zone_watermark_ok().

When balancing a node, kswapd considers the highest unbalanced zone to be the
classzone index. This will always be at least be the callers classzone_idx
and can be higher. However, sleeping_prematurely() always considers the
lowest zone (e.g. ZONE_DMA) to be the classzone index. This means that
sleeping_prematurely() can consider a zone to be balanced that is unusable
by the allocation request that originally woke kswapd. This patch changes
sleeping_prematurely() to use a classzone_idx matching the value it used
in balance_pgdat().

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
---
mm/vmscan.c | 19 +++++++++++--------
1 files changed, 11 insertions(+), 8 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d7b0a3c..e25b3ac 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2132,7 +2132,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
}

/* is kswapd sleeping prematurely? */
-static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
+static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
+ int classzone_idx)
{
int i;
unsigned long balanced = 0;
@@ -2140,7 +2141,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)

/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
- return 1;
+ return true;

/* Check the watermark levels */
for (i = 0; i < pgdat->nr_zones; i++) {
@@ -2161,7 +2162,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
}

if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
- 0, 0))
+ classzone_idx, 0))
all_zones_ok = false;
else
balanced += zone->present_pages;
@@ -2199,7 +2200,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
* of pages is balanced across the zones.
*/
static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
- int classzone_idx)
+ int *classzone_idx)
{
int all_zones_ok;
unsigned long balanced;
@@ -2262,6 +2263,7 @@ loop_again:
if (!zone_watermark_ok(zone, order,
high_wmark_pages(zone), 0, 0)) {
end_zone = i;
+ *classzone_idx = i;
break;
}
}
@@ -2346,7 +2348,7 @@ loop_again:
* spectulatively avoid congestion waits
*/
zone_clear_flag(zone, ZONE_CONGESTED);
- if (i <= classzone_idx)
+ if (i <= *classzone_idx)
balanced += zone->present_pages;
}

@@ -2441,6 +2443,7 @@ out:
* if another caller entered the allocator slow path while kswapd
* was awake, order will remain at the higher level
*/
+ *classzone_idx = end_zone;
return order;
}

@@ -2514,7 +2517,7 @@ static int kswapd(void *p)
long remaining = 0;

/* Try to sleep for a short interval */
- if (!sleeping_prematurely(pgdat, order, remaining)) {
+ if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
remaining = schedule_timeout(HZ/10);
finish_wait(&pgdat->kswapd_wait, &wait);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
@@ -2525,7 +2528,7 @@ static int kswapd(void *p)
* premature sleep. If not, then go fully
* to sleep until explicitly woken up
*/
- if (!sleeping_prematurely(pgdat, order, remaining)) {
+ if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
schedule();
} else {
@@ -2553,7 +2556,7 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
- order = balance_pgdat(pgdat, order, classzone_idx);
+ order = balance_pgdat(pgdat, order, &classzone_idx);
}
}
return 0;
--
1.7.1


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