[PATCH] Re: kswapd stuck using 100% CPU
From: Rik van Riel <hidden>
Date: 2012-03-24 14:26:54
Also in:
lkml
Subsystem:
memory management, memory management - mglru (multi-gen lru), memory management - reclaim, the rest · Maintainers:
Andrew Morton, Johannes Weiner, Linus Torvalds
On Sat, 24 Mar 2012 13:03:53 +1100 Anton Blanchard [off-list ref] wrote:
I booted the latest git today on a ppc64 box. When I pushed it into swap I noticed both kswapd's were using 100% CPU and the soft lockup detector suggested it was stuck in balance_pgdat: BUG: soft lockup - CPU#7 stuck for 23s! [kswapd1:359] Call Trace: [c00000000015e190] .balance_pgdat+0x150/0x940 [c00000000015eb2c] .kswapd+0x1ac/0x490 [c00000000009edbc] .kthread+0xbc/0xd0 [c00000000002142c] .kernel_thread+0x54/0x70
Are you running without CONFIG_COMPACTION enabled by any chance? Because if you do, the stub function compaction_suitable will always return COMPACT_SKIPPED:
quoted hunk ↗ jump to hunk
I haven't had time to bisect but I did notice we were looping here:+++ b/mm/vmscan.c@@ -2945,9 +2959,11 @@ out: if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; +#if 0 /* Would compaction fail due to lack of free memory? */ if (compaction_suitable(zone, order) == COMPACT_SKIPPED) goto loop_again; +#endif
The patch below should fix it. ----- Only test compaction_suitable if the kernel is built with CONFIG_COMPACTION, otherwise the stub compaction_suitable function will always return COMPACT_SKIPPED and send kswapd into an infinite loop. Signed-off-by: Rik van Riel <redacted> Reported-by: Anton Blanchard <redacted>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7658fd6..33c332b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -2946,7 +2946,8 @@ out: continue; /* Would compaction fail due to lack of free memory? */ - if (compaction_suitable(zone, order) == COMPACT_SKIPPED) + if (COMPACTION_BUILD && + compaction_suitable(zone, order) == COMPACT_SKIPPED) goto loop_again; /* Confirm the zone is balanced for order-0 */ --
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