[PATCH v2 12/16] mm: multigenerational lru: eviction

Yu Zhao
2021-04-13T06:57:29Z

The eviction consumes old generations. Given an lruvec, the eviction
scans the pages on the per-zone lists indexed by either of min_seq[2].
It first tries to select a type based on the values of min_seq[2].
When anon and file types are both available from the same generation,
it selects the one that has a lower refault rate.

During a scan, the eviction sorts pages according to their generation
numbers, if the aging has found them referenced. It also moves pages
from the tiers that have higher refault rates than tier 0 to the next
generation. When it finds all the per-zone lists of a selected type
are empty, the eviction increments min_seq[2] indexed by this selected
type.

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
mm/vmscan.c | 341 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 341 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 31e1b4155677..6239b1acd84f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5468,6 +5468,347 @@ static bool walk_mm_list(struct lruvec *lruvec, unsigned long max_seq,
return true;
}

+/******************************************************************************
+ * the eviction
+ ******************************************************************************/
+
+static bool sort_page(struct page *page, struct lruvec *lruvec, int tier_to_isolate)
+{
+ bool success;
+ int gen = page_lru_gen(page);
+ int file = page_is_file_lru(page);
+ int zone = page_zonenum(page);
+ int tier = lru_tier_from_usage(page_tier_usage(page));
+ struct lrugen *lrugen = &lruvec->evictable;
+
+ VM_BUG_ON_PAGE(gen == -1, page);
+ VM_BUG_ON_PAGE(tier_to_isolate < 0, page);
+
+ /* a lazy-free page that has been written into? */
+ if (file && PageDirty(page) && PageAnon(page)) {
+ success = lru_gen_deletion(page, lruvec);
+ VM_BUG_ON_PAGE(!success, page);
+ SetPageSwapBacked(page);
+ add_page_to_lru_list_tail(page, lruvec);
+ return true;
+ }
+
+ /* page_update_gen() has updated the page? */
+ if (gen != lru_gen_from_seq(lrugen->min_seq[file])) {
+ list_move(&page->lru, &lrugen->lists[gen][file][zone]);
+ return true;
+ }
+
+ /* activate the page if its tier has a higher refault rate */
+ if (tier_to_isolate < tier) {
+ int sid = sid_from_seq_or_gen(gen);
+
+ page_inc_gen(page, lruvec, false);
+ WRITE_ONCE(lrugen->activated[sid][file][tier - 1],
+ lrugen->activated[sid][file][tier - 1] + thp_nr_pages(page));
+ inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file);
+ return true;
+ }
+
+ /*
+ * A page can't be immediately evicted, and page_inc_gen() will mark it
+ * for reclaim and hopefully writeback will write it soon if it's dirty.
+ */
+ if (PageLocked(page) || PageWriteback(page) || (file && PageDirty(page))) {
+ page_inc_gen(page, lruvec, true);
+ return true;
+ }
+
+ return false;
+}
+
+static bool should_skip_page(struct page *page, struct scan_control *sc)
+{
+ if (!sc->may_unmap && page_mapped(page))
+ return true;
+
+ if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) &&
+ (PageDirty(page) || (PageAnon(page) && !PageSwapCache(page))))
+ return true;
+
+ if (!get_page_unless_zero(page))
+ return true;
+
+ if (!TestClearPageLRU(page)) {
+ put_page(page);
+ return true;
+ }
+
+ return false;
+}
+
+static void isolate_page(struct page *page, struct lruvec *lruvec)
+{
+ bool success;
+
+ success = lru_gen_deletion(page, lruvec);
+ VM_BUG_ON_PAGE(!success, page);
+
+ if (PageActive(page)) {
+ ClearPageActive(page);
+ /* make sure shrink_page_list() rejects this page */
+ SetPageReferenced(page);
+ return;
+ }
+
+ /* make sure shrink_page_list() doesn't try to write this page */
+ ClearPageReclaim(page);
+ /* make sure shrink_page_list() doesn't reject this page */
+ ClearPageReferenced(page);
+}
+
+static int scan_lru_gen_pages(struct lruvec *lruvec, struct scan_control *sc,
+ long *nr_to_scan, int file, int tier,
+ struct list_head *list)
+{
+ bool success;
+ int gen, zone;
+ enum vm_event_item item;
+ int sorted = 0;
+ int scanned = 0;
+ int isolated = 0;
+ int batch_size = 0;
+ struct lrugen *lrugen = &lruvec->evictable;
+
+ VM_BUG_ON(!list_empty(list));
+
+ if (get_nr_gens(lruvec, file) == MIN_NR_GENS)
+ return -ENOENT;
+
+ gen = lru_gen_from_seq(lrugen->min_seq[file]);
+
+ for (zone = sc->reclaim_idx; zone >= 0; zone--) {
+ LIST_HEAD(moved);
+ int skipped = 0;
+ struct list_head *head = &lrugen->lists[gen][file][zone];
+
+ while (!list_empty(head)) {
+ struct page *page = lru_to_page(head);
+ int delta = thp_nr_pages(page);
+
+ VM_BUG_ON_PAGE(PageTail(page), page);
+ VM_BUG_ON_PAGE(PageUnevictable(page), page);
+ VM_BUG_ON_PAGE(PageActive(page), page);
+ VM_BUG_ON_PAGE(page_is_file_lru(page) != file, page);
+ VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
+
+ prefetchw_prev_lru_page(page, head, flags);
+
+ scanned += delta;
+
+ if (sort_page(page, lruvec, tier))
+ sorted += delta;
+ else if (should_skip_page(page, sc)) {
+ list_move(&page->lru, &moved);
+ skipped += delta;
+ } else {
+ isolate_page(page, lruvec);
+ list_add(&page->lru, list);
+ isolated += delta;
+ }
+
+ if (scanned >= *nr_to_scan || isolated >= SWAP_CLUSTER_MAX ||
+ ++batch_size == MAX_BATCH_SIZE)
+ break;
+ }
+
+ list_splice(&moved, head);
+ __count_zid_vm_events(PGSCAN_SKIP, zone, skipped);
+
+ if (scanned >= *nr_to_scan || isolated >= SWAP_CLUSTER_MAX ||
+ batch_size == MAX_BATCH_SIZE)
+ break;
+ }
+
+ success = try_inc_min_seq(lruvec, file);
+
+ item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
+ if (!cgroup_reclaim(sc))
+ __count_vm_events(item, scanned);
+ __count_memcg_events(lruvec_memcg(lruvec), item, scanned);
+ __count_vm_events(PGSCAN_ANON + file, scanned);
+
+ *nr_to_scan -= scanned;
+
+ if (*nr_to_scan <= 0 || success || isolated)
+ return isolated;
+ /*
+ * We may have trouble finding eligible pages due to reclaim_idx,
+ * may_unmap and may_writepage. The following check makes sure we won't
+ * be stuck if we aren't making enough progress.
+ */
+ return batch_size == MAX_BATCH_SIZE && sorted >= SWAP_CLUSTER_MAX ? 0 : -ENOENT;
+}
+
+static int get_tier_to_isolate(struct lruvec *lruvec, int file)
+{
+ int tier;
+ struct controller_pos sp, pv;
+
+ /*
+ * Ideally we don't want to evict upper tiers that have higher refault
+ * rates. However, we need to leave some margin for the fluctuation in
+ * refault rates. So we use a larger gain factor to make sure upper
+ * tiers are indeed more active. We choose 2 because the lowest upper
+ * tier would have twice of the refault rate of the base tier, according
+ * to their numbers of accesses.
+ */
+ read_controller_pos(&sp, lruvec, file, 0, 1);
+ for (tier = 1; tier < MAX_NR_TIERS; tier++) {
+ read_controller_pos(&pv, lruvec, file, tier, 2);
+ if (!positive_ctrl_err(&sp, &pv))
+ break;
+ }
+
+ return tier - 1;
+}
+
+static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_to_isolate)
+{
+ int file, tier;
+ struct controller_pos sp, pv;
+ int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness };
+
+ /*
+ * Compare the refault rates between the base tiers of anon and file to
+ * determine which type to evict. Also need to compare the refault rates
+ * of the upper tiers of the selected type with that of the base tier to
+ * determine which tier of the selected type to evict.
+ */
+ read_controller_pos(&sp, lruvec, 0, 0, gain[0]);
+ read_controller_pos(&pv, lruvec, 1, 0, gain[1]);
+ file = positive_ctrl_err(&sp, &pv);
+
+ read_controller_pos(&sp, lruvec, !file, 0, gain[!file]);
+ for (tier = 1; tier < MAX_NR_TIERS; tier++) {
+ read_controller_pos(&pv, lruvec, file, tier, gain[file]);
+ if (!positive_ctrl_err(&sp, &pv))
+ break;
+ }
+
+ *tier_to_isolate = tier - 1;
+
+ return file;
+}
+
+static int isolate_lru_gen_pages(struct lruvec *lruvec, struct scan_control *sc,
+ int swappiness, long *nr_to_scan, int *type_to_scan,
+ struct list_head *list)
+{
+ int i;
+ int file;
+ int isolated;
+ int tier = -1;
+ DEFINE_MAX_SEQ();
+ DEFINE_MIN_SEQ();
+
+ VM_BUG_ON(!seq_is_valid(lruvec));
+
+ if (max_nr_gens(max_seq, min_seq, swappiness) == MIN_NR_GENS)
+ return 0;
+ /*
+ * Try to select a type based on generations and swappiness, and if that
+ * fails, fall back to get_type_to_scan(). When anon and file are both
+ * available from the same generation, swappiness 200 is interpreted as
+ * anon first and swappiness 1 is interpreted as file first.
+ */
+ file = !swappiness || min_seq[0] > min_seq[1] ||
+ (min_seq[0] == min_seq[1] && swappiness != 200 &&
+ (swappiness == 1 || get_type_to_scan(lruvec, swappiness, &tier)));
+
+ if (tier == -1)
+ tier = get_tier_to_isolate(lruvec, file);
+
+ for (i = !swappiness; i < ANON_AND_FILE; i++) {
+ isolated = scan_lru_gen_pages(lruvec, sc, nr_to_scan, file, tier, list);
+ if (isolated >= 0)
+ break;
+
+ file = !file;
+ tier = get_tier_to_isolate(lruvec, file);
+ }
+
+ if (isolated < 0)
+ isolated = *nr_to_scan = 0;
+
+ *type_to_scan = file;
+
+ return isolated;
+}
+
+/* Main function used by foreground, background and user-triggered eviction. */
+static bool evict_lru_gen_pages(struct lruvec *lruvec, struct scan_control *sc,
+ int swappiness, long *nr_to_scan)
+{
+ int file;
+ int isolated;
+ int reclaimed;
+ LIST_HEAD(list);
+ struct page *page;
+ enum vm_event_item item;
+ struct reclaim_stat stat;
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+
+ spin_lock_irq(&lruvec->lru_lock);
+
+ isolated = isolate_lru_gen_pages(lruvec, sc, swappiness, nr_to_scan, &file, &list);
+ VM_BUG_ON(list_empty(&list) == !!isolated);
+
+ if (isolated)
+ __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, isolated);
+
+ spin_unlock_irq(&lruvec->lru_lock);
+
+ if (!isolated)
+ goto done;
+
+ reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false);
+ /*
+ * We need to prevent rejected pages from being added back to the same
+ * lists they were isolated from. Otherwise we may risk looping on them
+ * forever. We use PageActive() or !PageReferenced() && PageWorkingset()
+ * to tell lru_gen_addition() not to add them to the oldest generation.
+ */
+ list_for_each_entry(page, &list, lru) {
+ if (PageMlocked(page))
+ continue;
+
+ if (PageReferenced(page)) {
+ SetPageActive(page);
+ ClearPageReferenced(page);
+ } else {
+ ClearPageActive(page);
+ SetPageWorkingset(page);
+ }
+ }
+
+ spin_lock_irq(&lruvec->lru_lock);
+
+ move_pages_to_lru(lruvec, &list);
+
+ __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -isolated);
+
+ item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
+ if (!cgroup_reclaim(sc))
+ __count_vm_events(item, reclaimed);
+ __count_memcg_events(lruvec_memcg(lruvec), item, reclaimed);
+ __count_vm_events(PGSTEAL_ANON + file, reclaimed);
+
+ spin_unlock_irq(&lruvec->lru_lock);
+
+ mem_cgroup_uncharge_list(&list);
+ free_unref_page_list(&list);
+
+ sc->nr_reclaimed += reclaimed;
+done:
+ return *nr_to_scan > 0 && sc->nr_reclaimed < sc->nr_to_reclaim;
+}
+
/******************************************************************************
* state change
******************************************************************************/
--
2.31.1.295.g9ea45b61b8-goog