Clemens Ladisch wrote, on 22/02/11 18:07:
Arthur Marsh wrote:
I'm experiencing MIDI playback slow-downs when I'm observing kswapd0
active (a few percent of cpu in top output) in recent kernels.
I git-bisected the problem down to:
commit 5a03b051ed87e72b959f32a86054e1142ac4cf55
Author: Andrea Arcangeli<aarcange@xxxxxxxxxx>
Date: Thu Jan 13 15:47:11 2011 -0800
thp: use compaction in kswapd for GFP_ATOMIC order> 0
This takes advantage of memory compaction to properly generate pages of
order> 0 if regular page reclaim fails and priority level becomes more
severe and we don't reach the proper watermarks.
Signed-off-by: Andrea Arcangeli<aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds<torvalds@xxxxxxxxxxxxxxxxxxxx>
I ran git-bisect over the weekend, building and installing ALSA 1.0.24
with each kernel. After identifying the above commit, I rebuilt the 2.6
head with that commit reverted and verified that the problem was no
longer present.
Apparently, huge page compaction disables interrupts for much too long.
MIDI playback was via aplaymidi -p 17:0 to a Soundblaster Audigy 2 ZS
(SB0350) wavetable.
The ALSA sequencer uses either the system timer or an HR timer at 1 kHz
to deliver MIDI commands (notes); the wavetable driver requires its own
interrupts in regular 5.3 ms intervals.
Regards,
Clemens
Hi, Andrea Arcangeli's "z1" patch (attached) solved the problem for me,
even with significant swap activity.
Regards,
Arthur.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 17497d0..5718bca 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2385,7 +2385,6 @@ loop_again:
* cause too much scanning of the lower zones.
*/
for (i = 0; i <= end_zone; i++) {
- int compaction;
struct zone *zone = pgdat->node_zones + i;
int nr_slab;
@@ -2408,7 +2407,7 @@ loop_again:
* zone has way too many pages free already.
*/
if (!zone_watermark_ok_safe(zone, order,
- 8*high_wmark_pages(zone), end_zone, 0))
+ high_wmark_pages(zone), end_zone, 0))
shrink_zone(priority, zone, &sc);
reclaim_state->reclaimed_slab = 0;
nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
@@ -2416,24 +2415,23 @@ loop_again:
sc.nr_reclaimed += reclaim_state->reclaimed_slab;
total_scanned += sc.nr_scanned;
- compaction = 0;
+#if 0
if (order &&
zone_watermark_ok(zone, 0,
high_wmark_pages(zone),
end_zone, 0) &&
!zone_watermark_ok(zone, order,
high_wmark_pages(zone),
- end_zone, 0)) {
+ end_zone, 0))
compact_zone_order(zone,
order,
sc.gfp_mask, false,
COMPACT_MODE_KSWAPD);
- compaction = 1;
- }
+#endif
if (zone->all_unreclaimable)
continue;
- if (!compaction && nr_slab == 0 &&
+ if (nr_slab == 0 &&
!zone_reclaimable(zone))
zone->all_unreclaimable = 1;
/*
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