Synchronous memory compaction can be very expensive: it can iterate an enormous
amount of memory without aborting and it can wait on page locks and writeback to
complete if a pageblock cannot be defragmented.
Unfortunately, it's too expensive for pagefault for transparent hugepages and
it's much better to simply fallback to pages. On 128GB machines, we find that
synchronous memory compaction can take O(seconds) for a single thp fault.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2656,7 +2656,7 @@ rebalance:
/* Wait for some write requests to complete then retry */
wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/50);
goto rebalance;
- } else {
+ } else if (!(gfp_mask & __GFP_NO_KSWAPD)) {
/*
* High-order allocations do not necessarily loop after
* direct reclaim and reclaim/compaction depends on compaction
--
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