Vlastimil Babka figured out that when fragmentation score didn't go down across the proactive compaction i.e. when no progress is made, next wake up for proactive compaction is deferred for 1 << COMPACT_MAX_DEFER_SHIFT, i.e. 64 times, with each wakeup interval of HPAGE_FRAG_CHECK_INTERVAL_MSEC(=500). In each of this wakeup, it just decrement 'proactive_defer' counter and goes sleep i.e. it is getting woken to just decrement a counter. The same deferral time can also achieved by simply doing the HPAGE_FRAG_CHECK_INTERVAL_MSEC << COMPACT_MAX_DEFER_SHIFT thus unnecessary wakeup of kcompact thread is avoided thus also removes the need of 'proactive_defer' thread counter. Link: https://lore.kernel.org/linux-fsdevel/88abfdb6-2c13-b5a6-5b46-742d12d1c910@xxxxxxx/ Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> --- Changes in V1: o Removed the 'proactive_defer' thread counter by optimizing proactive o This is a resend as earlier it was clubbed with other changes posted at https://lore.kernel.org/patchwork/patch/1448789/ mm/compaction.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 621508e..db00dbf 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2885,7 +2885,8 @@ static int kcompactd(void *p) { pg_data_t *pgdat = (pg_data_t *)p; struct task_struct *tsk = current; - unsigned int proactive_defer = 0; + long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC); + long timeout = default_timeout; const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); @@ -2902,23 +2903,30 @@ static int kcompactd(void *p) trace_mm_compaction_kcompactd_sleep(pgdat->node_id); if (wait_event_freezable_timeout(pgdat->kcompactd_wait, - kcompactd_work_requested(pgdat), - msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) { + kcompactd_work_requested(pgdat), timeout)) { psi_memstall_enter(&pflags); kcompactd_do_work(pgdat); psi_memstall_leave(&pflags); + /* + * Reset the timeout value. The defer timeout by + * proactive compaction can effectively lost + * here but that is fine as the condition of the + * zone changed substantionally and carrying on + * with the previous defer is not useful. + */ + timeout = default_timeout; continue; } - /* kcompactd wait timeout */ + /* + * Start the proactive work with default timeout. Based + * on the fragmentation score, this timeout is updated. + */ + timeout = default_timeout; if (should_proactive_compact_node(pgdat)) { unsigned int prev_score, score; - if (proactive_defer) { - proactive_defer--; - continue; - } prev_score = fragmentation_score_node(pgdat); proactive_compact_node(pgdat); score = fragmentation_score_node(pgdat); @@ -2926,8 +2934,9 @@ static int kcompactd(void *p) * Defer proactive compaction if the fragmentation * score did not go down i.e. no progress made. */ - proactive_defer = score < prev_score ? - 0 : 1 << COMPACT_MAX_DEFER_SHIFT; + if (unlikely(score >= prev_score)) + timeout = + default_timeout << COMPACT_MAX_DEFER_SHIFT; } } -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
