The patch titled
Subject: mm, vmscan: only clear pgdat congested/dirty/writeback state when balanced
has been removed from the -mm tree. Its filename was
mm-vmscan-only-clear-pgdat-congested-dirty-writeback-state-when-balanced.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, vmscan: only clear pgdat congested/dirty/writeback state when balanced
A pgdat tracks if recent reclaim encountered too many dirty, writeback or
congested pages. The flags control whether kswapd writes pages back from
reclaim context, tags pages for immediate reclaim when IO completes,
whether processes block on wait_iff_congested and whether kswapd blocks
when too many pages marked for immediate reclaim are encountered.
The state is cleared in a check function with side-effects. With the
patch "mm, vmscan: fix zone balance check in prepare_kswapd_sleep", the
timing of when the bits get cleared changed. Due to the way the check
works, it'll clear the bits if ZONE_DMA is balanced for a GFP_DMA
allocation because it does not account for lowmem reserves properly.
For the simoop workload, kswapd is not stalling when it should due to the
premature clearing, writing pages from reclaim context like crazy and
generally being unhelpful.
This patch resets the pgdat bits related to page reclaim only when kswapd
is going to sleep. The comparison with simoop is then
4.11.0-rc1 4.11.0-rc1 4.11.0-rc1
vanilla fixcheck-v2 clear-v2
Amean p50-Read 21670074.18 ( 0.00%) 20464344.18 ( 5.56%) 19786774.76 ( 8.69%)
Amean p95-Read 25456267.64 ( 0.00%) 25721423.64 ( -1.04%) 24101956.27 ( 5.32%)
Amean p99-Read 29369064.73 ( 0.00%) 30174230.76 ( -2.74%) 27691872.71 ( 5.71%)
Amean p50-Write 1390.30 ( 0.00%) 1395.28 ( -0.36%) 1011.91 ( 27.22%)
Amean p95-Write 412901.57 ( 0.00%) 37737.74 ( 90.86%) 34874.98 ( 91.55%)
Amean p99-Write 6668722.09 ( 0.00%) 666489.04 ( 90.01%) 575449.60 ( 91.37%)
Amean p50-Allocation 78714.31 ( 0.00%) 86286.22 ( -9.62%) 84246.26 ( -7.03%)
Amean p95-Allocation 175533.51 ( 0.00%) 351812.27 (-100.42%) 400058.43 (-127.91%)
Amean p99-Allocation 247003.02 ( 0.00%) 6291171.56 (-2447.00%) 10905600.00 (-4315.17%)
Read latency is improved, write latency is mostly improved but allocation
latency is regressed. kswapd is still reclaiming inefficiently, pages are
being written back from writeback context and a host of other issues.
However, given the change, it needed to be spelled out why the side-effect
was moved.
Link: http://lkml.kernel.org/r/20170309075657.25121-3-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shantanu Goel <sgoel01@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
diff -puN mm/vmscan.c~mm-vmscan-only-clear-pgdat-congested-dirty-writeback-state-when-balanced mm/vmscan.c
--- a/mm/vmscan.c~mm-vmscan-only-clear-pgdat-congested-dirty-writeback-state-when-balanced
+++ a/mm/vmscan.c
@@ -3056,17 +3056,17 @@ static bool zone_balanced(struct zone *z
if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
return false;
- /*
- * If any eligible zone is balanced then the node is not considered
- * to be congested or dirty
- */
- clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
- clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
- clear_bit(PGDAT_WRITEBACK, &zone->zone_pgdat->flags);
-
return true;
}
+/* Clear pgdat state for congested, dirty or under writeback. */
+static void clear_pgdat_congested(pg_data_t *pgdat)
+{
+ clear_bit(PGDAT_CONGESTED, &pgdat->flags);
+ clear_bit(PGDAT_DIRTY, &pgdat->flags);
+ clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
+}
+
/*
* Prepare kswapd for sleeping. This verifies that there are no processes
* waiting in throttle_direct_reclaim() and that watermarks have been met.
@@ -3103,8 +3103,10 @@ static bool prepare_kswapd_sleep(pg_data
if (!managed_zone(zone))
continue;
- if (zone_balanced(zone, order, classzone_idx))
+ if (zone_balanced(zone, order, classzone_idx)) {
+ clear_pgdat_congested(pgdat);
return true;
+ }
}
return false;
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
