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    Subjectkswapd stuck using 100% CPU

    Hi,

    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

    I haven't had time to bisect but I did notice we were looping here:

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 7658fd6..c92bad2 100644
    --- a/mm/vmscan.c
    +++ 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

    /* Confirm the zone is balanced for order-0 */
    if (!zone_watermark_ok(zone, 0,

    After commenting it out the box is happy again.

    Anton


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