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    SubjectRe: [PATCH 4/4] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA
    Date
    > +
    > +zone_reclaim_interval:
    > +
    > +The time allowed for off-node allocations after zone reclaim
    > +has failed to reclaim enough pages to allow a local allocation.
    > +
    > +Time is set in seconds and set by default to 30 seconds.
    > +
    > +Reduce the interval if undesired off-node allocations occur or
    > +set to 0 to always try and reclaim pages for node-local memory.
    > +However, too frequent scans will have a negative impact on
    > +off-node allocation performance and manifest as high CPU usage.
    > +

    good documentaion :)

    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

    -kosaki



    > ============ End of Document =================================
    > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    > index 8895985..3a53e1c 100644
    > --- a/include/linux/mmzone.h
    > +++ b/include/linux/mmzone.h
    > @@ -335,6 +335,15 @@ struct zone {
    > atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
    >
    > /*
    > + * timestamp (in jiffies) of the last zone_reclaim that scanned
    > + * but failed to free enough pages. This is used to avoid repeated
    > + * scans when zone_reclaim() is unable to detect in advance that
    > + * the scanning is useless. This can happen for example if a zone
    > + * has large numbers of clean unmapped file pages on tmpfs
    > + */
    > + unsigned long zone_reclaim_failure;
    > +
    > + /*
    > * prev_priority holds the scanning priority for this zone. It is
    > * defined as the scanning priority at which we achieved our reclaim
    > * target at the previous try_to_free_pages() or balance_pgdat()
    > diff --git a/include/linux/swap.h b/include/linux/swap.h
    > index c88b366..28a01e3 100644
    > --- a/include/linux/swap.h
    > +++ b/include/linux/swap.h
    > @@ -225,6 +225,7 @@ extern long vm_total_pages;
    >
    > #ifdef CONFIG_NUMA
    > extern int zone_reclaim_mode;
    > +extern int zone_reclaim_interval;
    > extern int sysctl_min_unmapped_ratio;
    > extern int sysctl_min_slab_ratio;
    > extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
    > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
    > index 0554886..2afffa5 100644
    > --- a/kernel/sysctl.c
    > +++ b/kernel/sysctl.c
    > @@ -1221,6 +1221,15 @@ static struct ctl_table vm_table[] = {
    > .extra1 = &zero,
    > },
    > {
    > + .ctl_name = CTL_UNNUMBERED,
    > + .procname = "zone_reclaim_interval",
    > + .data = &zone_reclaim_interval,
    > + .maxlen = sizeof(zone_reclaim_interval),
    > + .mode = 0644,
    > + .proc_handler = &proc_dointvec_jiffies,
    > + .strategy = &sysctl_jiffies,
    > + },
    > + {
    > .ctl_name = VM_MIN_UNMAPPED,
    > .procname = "min_unmapped_ratio",
    > .data = &sysctl_min_unmapped_ratio,
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 8be4582..5fa4843 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -2315,6 +2315,13 @@ int zone_reclaim_mode __read_mostly;
    > #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
    >
    > /*
    > + * Minimum time between zone_reclaim() scans that failed. Ordinarily, a
    > + * scan will not fail because it will be determined in advance if it can
    > + * succeeed but this does not always work. See mmzone.h
    > + */
    > +int zone_reclaim_interval __read_mostly = 30*HZ;
    > +
    > +/*
    > * Priority for ZONE_RECLAIM. This determines the fraction of pages
    > * of a node considered for each zone_reclaim. 4 scans 1/16th of
    > * a zone.
    > @@ -2464,6 +2471,15 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    > zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
    > return ZONE_RECLAIM_FULL;
    >
    > + /* Watch for jiffie wraparound */
    > + if (unlikely(jiffies < zone->zone_reclaim_failure))
    > + zone->zone_reclaim_failure = jiffies;
    > +
    > + /* Do not attempt a scan if scanning failed recently */
    > + if (time_before(jiffies,
    > + zone->zone_reclaim_failure + zone_reclaim_interval))
    > + return ZONE_RECLAIM_FULL;
    > +
    > if (zone_is_all_unreclaimable(zone))
    > return ZONE_RECLAIM_FULL;
    >
    > @@ -2491,6 +2507,14 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    >
    > if (!ret) {
    > count_vm_events(PGSCAN_ZONERECLAIM_FAILED, 1);
    > +
    > + /*
    > + * We were unable to reclaim enough pages to stay on node and
    > + * unable to detect in advance that the scan would fail. Allow
    > + * off node accesses for zone_reclaim_inteval jiffies before
    > + * trying zone_reclaim() again
    > + */
    > + zone->zone_reclaim_failure = jiffies;
    > }
    >
    > return ret;
    > --
    > 1.5.6.5
    >





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