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authorAndrea Arcangeli <aarcange@redhat.com>2011-03-22 16:33:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:05 -0700
commitb2eef8c0d09101bbbff2531c097543aedde0b525 (patch)
treeba0cbc88a8f66dc53c915509d90b3c4eeae8e7f1
parent602605a42ea4c299aeed4d806c49fb9dd18cd204 (diff)
downloadop-kernel-dev-b2eef8c0d09101bbbff2531c097543aedde0b525.zip
op-kernel-dev-b2eef8c0d09101bbbff2531c097543aedde0b525.tar.gz
mm: compaction: minimise the time IRQs are disabled while isolating pages for migration
compaction_alloc() isolates pages for migration in isolate_migratepages. While it's scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Tests show this to be true for the most part but contention times on the LRU lock can be increased. Before this patch, the IRQ disabled times for a simple test looked like Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 This patch reduces the worst-case IRQs-disabled latencies by releasing the lock every SWAP_CLUSTER_MAX pages that are scanned and releasing the CPU if necessary. The cost of this is that the processing performing compaction will be slower but IRQs being disabled for too long a time has worse consequences as the following report shows; Total sampled time IRQs off (not real total time): 4367 Event shrink_inactive_list..shrink_zone 881 us count 1 Event shrink_inactive_list..shrink_zone 875 us count 1 Event shrink_inactive_list..shrink_zone 868 us count 1 Event shrink_inactive_list..shrink_zone 555 us count 1 Event split_huge_page..add_to_swap 495 us count 1 Event compact_zone..compact_zone_order 269 us count 1 Event split_huge_page..add_to_swap 266 us count 1 Event shrink_inactive_list..shrink_zone 85 us count 1 Event save_args..call_softirq 36 us count 2 Event __wake_up..__wake_up 1 us count 1 [akpm@linux-foundation.org: simplify with s/unlocked/locked/] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Arthur Marsh <arthur.marsh@internode.on.net> Cc: Clemens Ladisch <cladisch@googlemail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/compaction.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index b27802e..021a296 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -277,9 +277,27 @@ static unsigned long isolate_migratepages(struct zone *zone,
}
/* Time to isolate some pages for migration */
+ cond_resched();
spin_lock_irq(&zone->lru_lock);
for (; low_pfn < end_pfn; low_pfn++) {
struct page *page;
+ bool locked = true;
+
+ /* give a chance to irqs before checking need_resched() */
+ if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
+ spin_unlock_irq(&zone->lru_lock);
+ locked = false;
+ }
+ if (need_resched() || spin_is_contended(&zone->lru_lock)) {
+ if (locked)
+ spin_unlock_irq(&zone->lru_lock);
+ cond_resched();
+ spin_lock_irq(&zone->lru_lock);
+ if (fatal_signal_pending(current))
+ break;
+ } else if (!locked)
+ spin_lock_irq(&zone->lru_lock);
+
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
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