BACKPORT: mm: multi-gen LRU: retry pages written back while isolated
The page reclaim isolates a batch of pages from the tail of one of the
LRU lists and works on those pages one by one. For a suitable
swap-backed page, if the swap device is async, it queues that page for
writeback. After the page reclaim finishes an entire batch, it puts back
the pages it queued for writeback to the head of the original LRU list.
In the meantime, the page writeback flushes the queued pages also by
batches. Its batching logic is independent from that of the page reclaim.
For each of the pages it writes back, the page writeback calls
rotate_reclaimable_page() which tries to rotate a page to the tail.
rotate_reclaimable_page() only works for a page after the page reclaim
has put it back. If an async swap device is fast enough, the page
writeback can finish with that page while the page reclaim is still
working on the rest of the batch containing it. In this case, that page
will remain at the head and the page reclaim will not retry it before
reaching there.
This patch adds a retry to evict_pages(). After evict_pages() has
finished an entire batch and before it puts back pages it cannot free
immediately, it retries those that may have missed the rotation.
Before this patch, ~60% of pages swapped to an Intel Optane missed
rotate_reclaimable_page(). After this patch, ~99% of missed pages were
reclaimed upon retry.
This problem affects relatively slow async swap devices like Samsung 980
Pro much less and does not affect sync swap devices like zram or zswap at
all.
Link: https://lkml.kernel.org/r/20221116013808.3995280-1-yuzhao@google.com
Fixes: ac35a4902374 ("mm: multi-gen LRU: minimal implementation")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: "Yin, Fengwei" <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Bug: 274865848
(cherry picked from commit 359a5e1416caaf9ce28396a65ed3e386cc5de663)
[Yu: Resolve conflicts over absence of folios on 5.15]
Change-Id: Ife11b13e2612c84a2de1727781983f66a06141bb
Signed-off-by: T.J. Mercier <tjmercier@google.com>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c5ab1e7..bac175d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4774,10 +4774,13 @@ static int evict_pages(struct lruvec *lruvec, struct scan_control *sc, int swapp
int scanned;
int reclaimed;
LIST_HEAD(list);
+ LIST_HEAD(clean);
struct page *page;
+ struct page *next;
enum vm_event_item item;
struct reclaim_stat stat;
struct lru_gen_mm_walk *walk;
+ bool skip_retry = false;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
@@ -4794,20 +4797,37 @@ static int evict_pages(struct lruvec *lruvec, struct scan_control *sc, int swapp
if (list_empty(&list))
return scanned;
-
+retry:
reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false);
+ sc->nr_reclaimed += reclaimed;
- list_for_each_entry(page, &list, lru) {
- /* restore LRU_REFS_FLAGS cleared by isolate_page() */
- if (PageWorkingset(page))
- SetPageReferenced(page);
+ list_for_each_entry_safe_reverse(page, next, &list, lru) {
+ if (!page_evictable(page)) {
+ list_del(&page->lru);
+ putback_lru_page(page);
+ continue;
+ }
- /* don't add rejected pages to the oldest generation */
if (PageReclaim(page) &&
- (PageDirty(page) || PageWriteback(page)))
- ClearPageActive(page);
- else
- SetPageActive(page);
+ (PageDirty(page) || PageWriteback(page))) {
+ /* restore LRU_REFS_FLAGS cleared by isolate_page() */
+ if (PageWorkingset(page))
+ SetPageReferenced(page);
+ continue;
+ }
+
+ if (skip_retry || PageActive(page) || PageReferenced(page) ||
+ page_mapped(page) || PageLocked(page) ||
+ PageDirty(page) || PageWriteback(page)) {
+ /* don't add rejected pages to the oldest generation */
+ set_mask_bits(&page->flags, LRU_REFS_MASK | LRU_REFS_FLAGS,
+ BIT(PG_active));
+ continue;
+ }
+
+ /* retry pages that may have missed rotate_reclaimable_page() */
+ list_move(&page->lru, &clean);
+ sc->nr_scanned -= thp_nr_pages(page);
}
spin_lock_irq(&lruvec->lru_lock);
@@ -4829,7 +4849,13 @@ static int evict_pages(struct lruvec *lruvec, struct scan_control *sc, int swapp
mem_cgroup_uncharge_list(&list);
free_unref_page_list(&list);
- sc->nr_reclaimed += reclaimed;
+ INIT_LIST_HEAD(&list);
+ list_splice_init(&clean, &list);
+
+ if (!list_empty(&list)) {
+ skip_retry = true;
+ goto retry;
+ }
if (need_swapping && type == LRU_GEN_ANON)
*need_swapping = true;