Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation

+static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq)
+{
+       int prev, next;
+       int type, zone;
+       struct lru_gen_struct *lrugen = &lruvec->lrugen;
+
+       spin_lock_irq(&lruvec->lru_lock);
+
+       VM_BUG_ON(!seq_is_valid(lruvec));
+
+       if (max_seq != lrugen->max_seq)
+               goto unlock;
+
+       inc_min_seq(lruvec);
+
+       /* update the active/inactive LRU sizes for compatibility */
+       prev = lru_gen_from_seq(lrugen->max_seq - 1);
+       next = lru_gen_from_seq(lrugen->max_seq + 1);
+
+       for (type = 0; type < ANON_AND_FILE; type++) {
+               for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+                       enum lru_list lru = type * LRU_INACTIVE_FILE;
+                       long delta = lrugen->nr_pages[prev][type][zone] -
+                                    lrugen->nr_pages[next][type][zone];

this is confusing to me. does lrugen->nr_pages[next][type][zone] have a
chance to be none-zero even before max_seq is increased? some pages
can be in the next generation before the generation is born?

isn't it a bug if(lrugen->nr_pages[next][type][zone] > 0)? shouldn't it be？

delta = lrugen->nr_pages[prev][type][zone]；

+
+                       if (!delta)
+                               continue;
+
+                       __update_lru_size(lruvec, lru, zone, delta);
+                       __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta);
+               }
+       }
+
+       for (type = 0; type < ANON_AND_FILE; type++)
+               reset_ctrl_pos(lruvec, type, false);
+
+       /* make sure preceding modifications appear */
+       smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
+unlock:
+       spin_unlock_irq(&lruvec->lru_lock);
+}

Thanks
Barry

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