Yu Zhao <yuzhao@xxxxxxxxxx> writes:
[snip]
> +/* Main function used by foreground, background and user-triggered aging. */
> +static bool walk_mm_list(struct lruvec *lruvec, unsigned long next_seq,
> + struct scan_control *sc, int swappiness)
> +{
> + bool last;
> + struct mm_struct *mm = NULL;
> + int nid = lruvec_pgdat(lruvec)->node_id;
> + struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> + struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
> +
> + VM_BUG_ON(next_seq > READ_ONCE(lruvec->evictable.max_seq));
> +
> + /*
> + * For each walk of the mm list of a memcg, we decrement the priority
> + * of its lruvec. For each walk of memcgs in kswapd, we increment the
> + * priorities of all lruvecs.
> + *
> + * So if this lruvec has a higher priority (smaller value), it means
> + * other concurrent reclaimers (global or memcg reclaim) have walked
> + * its mm list. Skip it for this priority to balance the pressure on
> + * all memcgs.
> + */
> +#ifdef CONFIG_MEMCG
> + if (!mem_cgroup_disabled() && !cgroup_reclaim(sc) &&
> + sc->priority > atomic_read(&lruvec->evictable.priority))
> + return false;
> +#endif
> +
> + do {
> + last = get_next_mm(lruvec, next_seq, swappiness, &mm);
> + if (mm)
> + walk_mm(lruvec, mm, swappiness);
> +
> + cond_resched();
> + } while (mm);
It appears that we need to scan the whole address space of multiple
processes in this loop?
If so, I have some concerns about the duration of the function. Do you
have some number of the distribution of the duration of the function?
And may be the number of mm_struct and the number of pages scanned.
In comparison, in the traditional LRU algorithm, for each round, only a
small subset of the whole physical memory is scanned.
Best Regards,
Huang, Ying
> +
> + if (!last) {
> + /* foreground aging prefers not to wait unless "necessary" */
> + if (!current_is_kswapd() && sc->priority < DEF_PRIORITY - 2)
> + wait_event_killable(mm_list->nodes[nid].wait,
> + next_seq < READ_ONCE(lruvec->evictable.max_seq));
> +
> + return next_seq < READ_ONCE(lruvec->evictable.max_seq);
> + }
> +
> + VM_BUG_ON(next_seq != READ_ONCE(lruvec->evictable.max_seq));
> +
> + inc_max_seq(lruvec);
> +
> +#ifdef CONFIG_MEMCG
> + if (!mem_cgroup_disabled())
> + atomic_add_unless(&lruvec->evictable.priority, -1, 0);
> +#endif
> +
> + /* order against inc_max_seq() */
> + smp_mb();
> + /* either we see any waiters or they will see updated max_seq */
> + if (waitqueue_active(&mm_list->nodes[nid].wait))
> + wake_up_all(&mm_list->nodes[nid].wait);
> +
> + wakeup_flusher_threads(WB_REASON_VMSCAN);
> +
> + return true;
> +}
> +
[snip]
Best Regards,
Huang, Ying
