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    SubjectRe: [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps
    On Thu, Jun 16, 2016 at 09:30:33AM +0100, Mel Gorman wrote:
    > > >@@ -2727,7 +2727,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
    > > >
    > > > /* kswapd must be awake if processes are being throttled */
    > > > if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
    > > >- pgdat->classzone_idx = min(pgdat->classzone_idx,
    > > >+ pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
    > > > (enum zone_type)ZONE_NORMAL);
    > > > wake_up_interruptible(&pgdat->kswapd_wait);
    > > > }
    > > >@@ -3211,6 +3211,12 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order,
    > > >
    > > > prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
    > > >
    > > >+ /* If kswapd has not been woken recently, then full sleep */
    > > >+ if (classzone_idx == -1) {
    > > >+ classzone_idx = balanced_classzone_idx = MAX_NR_ZONES - 1;
    > > >+ goto full_sleep;
    > >
    > > This will skip the wakeup_kcompactd() part.
    > >
    >
    > I wrestled with this one. I decided to leave it alone on the grounds
    > that if kswapd has not been woken recently then compaction efforts also
    > have not failed and kcompactd is not required.
    >

    And I was wrong. There needs to be a call to wakeup_kcompactd there to
    cover the case where there was a single high-order allocation request
    that failed and woke kswapd.

    --
    Mel Gorman
    SUSE Labs

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