On Mon, 12 Apr 2021, chukaiping wrote:
> Currently the proactive compaction order is fixed to
> COMPACTION_HPAGE_ORDER(9), it's OK in most machines with lots of
> normal 4KB memory, but it's too high for the machines with small
> normal memory, for example the machines with most memory configured
> as 1GB hugetlbfs huge pages. In these machines the max order of
> free pages is often below 9, and it's always below 9 even with hard
> compaction. This will lead to proactive compaction be triggered very
> frequently. In these machines we only care about order of 3 or 4.
> This patch export the oder to proc and let it configurable
> by user, and the default value is still COMPACTION_HPAGE_ORDER.
>
I'm curious why you have proactive compaction enabled at all in this case?
The order-9 threshold is likely to optimize for hugepage availability, but
in your setup it appears that's not a goal.
So what benefit does proactive compaction provide if only done for order-3
or order-4?
> Signed-off-by: chukaiping <chukaiping@xxxxxxxxx>
> ---
> include/linux/compaction.h | 1 +
> kernel/sysctl.c | 10 ++++++++++
> mm/compaction.c | 7 ++++---
> 3 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index ed4070e..151ccd1 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -83,6 +83,7 @@ static inline unsigned long compact_gap(unsigned int order)
> #ifdef CONFIG_COMPACTION
> extern int sysctl_compact_memory;
> extern unsigned int sysctl_compaction_proactiveness;
> +extern unsigned int sysctl_compaction_order;
> extern int sysctl_compaction_handler(struct ctl_table *table, int write,
> void *buffer, size_t *length, loff_t *ppos);
> extern int sysctl_extfrag_threshold;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 62fbd09..277df31 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -114,6 +114,7 @@
> static int __maybe_unused neg_one = -1;
> static int __maybe_unused two = 2;
> static int __maybe_unused four = 4;
> +static int __maybe_unused ten = 10;
> static unsigned long zero_ul;
> static unsigned long one_ul = 1;
> static unsigned long long_max = LONG_MAX;
> @@ -2871,6 +2872,15 @@ int proc_do_static_key(struct ctl_table *table, int write,
> .extra2 = &one_hundred,
> },
> {
> + .procname = "compaction_order",
> + .data = &sysctl_compaction_order,
> + .maxlen = sizeof(sysctl_compaction_order),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = &ten,
> + },
> + {
> .procname = "extfrag_threshold",
> .data = &sysctl_extfrag_threshold,
> .maxlen = sizeof(int),
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e04f447..a192996 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1925,16 +1925,16 @@ static bool kswapd_is_running(pg_data_t *pgdat)
>
> /*
> * A zone's fragmentation score is the external fragmentation wrt to the
> - * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
> + * sysctl_compaction_order. It returns a value in the range [0, 100].
> */
> static unsigned int fragmentation_score_zone(struct zone *zone)
> {
> - return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> + return extfrag_for_order(zone, sysctl_compaction_order);
> }
>
> /*
> * A weighted zone's fragmentation score is the external fragmentation
> - * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
> + * wrt to the sysctl_compaction_order scaled by the zone's size. It
> * returns a value in the range [0, 100].
> *
> * The scaling factor ensures that proactive compaction focuses on larger
> @@ -2666,6 +2666,7 @@ static void compact_nodes(void)
> * background. It takes values in the range [0, 100].
> */
> unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
> +unsigned int __read_mostly sysctl_compaction_order = COMPACTION_HPAGE_ORDER;
>
> /*
> * This is the entry point for compacting all nodes via
> --
> 1.7.1
>
>
