Andrea Arcangeli <aarca...@redhat.com> writes:
> +/*
> + * In this function we build a temporal CPU_node<->page relation by
> + * using a two-stage autonuma_last_nid filter to remove short/unlikely
> + * relations.
> + *
> + * Using P(p) ~ n_p / n_t as per frequentest probability, we can
> + * equate a node's CPU usage of a particular page (n_p) per total
> + * usage of this page (n_t) (in a given time-span) to a probability.
> + *
> + * Our periodic faults will then sample this probability and getting
> + * the same result twice in a row, given these samples are fully
> + * independent, is then given by P(n)^2, provided our sample period
> + * is sufficiently short compared to the usage pattern.
> + *
> + * This quadric squishes small probabilities, making it less likely
> + * we act on an unlikely CPU_node<->page relation.
> + */
The code does not seem to do what the comment describes.
> +static inline bool last_nid_set(struct page *page, int this_nid)
> +{
> + bool ret = true;
> + int autonuma_last_nid = ACCESS_ONCE(page->autonuma_last_nid);
> + VM_BUG_ON(this_nid < 0);
> + VM_BUG_ON(this_nid >= MAX_NUMNODES);
> + if (autonuma_last_nid >= 0 && autonuma_last_nid != this_nid) {
> + int migrate_nid = ACCESS_ONCE(page->autonuma_migrate_nid);
> + if (migrate_nid >= 0)
> + __autonuma_migrate_page_remove(page);
> + ret = false;
> + }
> + if (autonuma_last_nid != this_nid)
> + ACCESS_ONCE(page->autonuma_last_nid) = this_nid;
> + return ret;
> +}
> +
> + /*
> + * Take the lock with irqs disabled to avoid a lock
> + * inversion with the lru_lock. The lru_lock is taken
> + * before the autonuma_migrate_lock in
> + * split_huge_page. If we didn't disable irqs, the
> + * lru_lock could be taken by interrupts after we have
> + * obtained the autonuma_migrate_lock here.
> + */
Which interrupt code takes the lru_lock? That sounds like a bug.
--
a...@linux.intel.com -- Speaking for myself only
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