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    SubjectRe: mm: 5.16 regression: reclaim_throttle leads to stall in near-OOM conditions
    On Wed, Nov 24, 2021 at 07:54:49PM +0900, Alexey Avramov wrote:
    > > it does eventually get killed OOM
    >
    > However, a full minute freeze can be a great evil in many situations -
    > during such a freeze, the system is completely unresponsive.
    >
    > So my next question is: How reasonable is the value MAX_RECLAIM_RETRIES?
    > Is it also get "out of thin air"?
    >

    The value is out of thin air but adjusting it may reintroduce issues
    with kswapd running at 100% CPU.

    > And would it make sense to have buttons to adjust the timeouts?

    I don't think we should introduce a tunable for something like this,
    it'll be impossible to use properly but can you test this?

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 07db03883062..aa72c0f39dcc 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1058,6 +1058,14 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
    break;
    case VMSCAN_THROTTLE_NOPROGRESS:
    timeout = HZ/2;
    +
    + /*
    + * If kswapd is disabled, use the minimum timeout as the
    + * system may be at or near OOM.
    + */
    + if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
    + timeout = 1;
    +
    break;
    case VMSCAN_THROTTLE_ISOLATED:
    timeout = HZ/50;
    @@ -3395,7 +3403,7 @@ static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
    return;

    /* Throttle if making no progress at high prioities. */
    - if (sc->priority < DEF_PRIORITY - 2)
    + if (sc->priority < DEF_PRIORITY - 2 && !sc->nr_reclaimed)
    reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
    }

    @@ -3415,6 +3423,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    unsigned long nr_soft_scanned;
    gfp_t orig_mask;
    pg_data_t *last_pgdat = NULL;
    + pg_data_t *first_pgdat = NULL;

    /*
    * If the number of buffer_heads in the machine exceeds the maximum
    @@ -3478,14 +3487,18 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    /* need some check for avoid more shrink_zone() */
    }

    + if (!first_pgdat)
    + first_pgdat = zone->zone_pgdat;
    +
    /* See comment about same check for global reclaim above */
    if (zone->zone_pgdat == last_pgdat)
    continue;
    last_pgdat = zone->zone_pgdat;
    shrink_node(zone->zone_pgdat, sc);
    - consider_reclaim_throttle(zone->zone_pgdat, sc);
    }

    + consider_reclaim_throttle(first_pgdat, sc);
    +
    /*
    * Restore to original mask to avoid the impact on the caller if we
    * promoted it to __GFP_HIGHMEM.
    \
     
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      Last update: 2021-11-24 12:51    [W:2.714 / U:0.052 seconds]
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