On Wed, Jan 25, 2023 at 1:13 PM Yu Zhao [off-list ref] wrote:

On Mon, Jan 23, 2023 at 7:11 PM Nhat Pham [off-list ref] wrote:

quoted

In preparation for computing recently evicted pages in cachestat,
refactor workingset_refault and lru_gen_refault to expose a helper
function that would test if an evicted page is recently evicted.

Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/swap.h |   1 +
 mm/workingset.c      | 142 +++++++++++++++++++++++++++++--------------
 2 files changed, 97 insertions(+), 46 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index a18cf4b7c724..dae6f6f955eb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h

@@ -361,6 +361,7 @@ static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
 }

 /* linux/mm/workingset.c */
+bool workingset_test_recent(void *shadow, bool file, bool *workingset);
 void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
 void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg);
 void workingset_refault(struct folio *folio, void *shadow);

diff --git a/mm/workingset.c b/mm/workingset.c
index 79585d55c45d..2f2d94867366 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c

@@ -244,6 +244,30 @@ static void *lru_gen_eviction(struct folio *folio)
        return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
 }

+/*
+ * Test if the folio is recently evicted.
+ *
+ * As a side effect, also populates the references with
+ * values unpacked from the shadow of the evicted folio.
+ */
+static bool lru_gen_test_recent(void *shadow, bool file, int *memcgid,
+               struct pglist_data **pgdat, unsigned long *token, bool *workingset)
+{
+       struct mem_cgroup *eviction_memcg;
+       struct lruvec *lruvec;
+       struct lru_gen_struct *lrugen;
+       unsigned long min_seq;
+
+       unpack_shadow(shadow, memcgid, pgdat, token, workingset);
+       eviction_memcg = mem_cgroup_from_id(*memcgid);
+
+       lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
+       lrugen = &lruvec->lrugen;
+
+       min_seq = READ_ONCE(lrugen->min_seq[file]);
+       return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH));
+}
+
 static void lru_gen_refault(struct folio *folio, void *shadow)
 {
        int hist, tier, refs;

@@ -258,23 +282,22 @@ static void lru_gen_refault(struct folio *folio, void *shadow)
        int type = folio_is_file_lru(folio);
        int delta = folio_nr_pages(folio);

-       unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset);
-
-       if (pgdat != folio_pgdat(folio))
-               return;
-
        rcu_read_lock();

+       if (!lru_gen_test_recent(shadow, type, &memcg_id, &pgdat, &token,
+                       &workingset))
+               goto unlock;
+
        memcg = folio_memcg_rcu(folio);
        if (memcg_id != mem_cgroup_id(memcg))
                goto unlock;

+       if (pgdat != folio_pgdat(folio))
+               return;
+
        lruvec = mem_cgroup_lruvec(memcg, pgdat);
        lrugen = &lruvec->lrugen;
-
        min_seq = READ_ONCE(lrugen->min_seq[type]);
-       if ((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)))
-               goto unlock;

        hist = lru_hist_from_seq(min_seq);
        /* see the comment in folio_lru_refs() */

@@ -306,6 +329,12 @@ static void *lru_gen_eviction(struct folio *folio)
        return NULL;
 }

+static bool lru_gen_test_recent(void *shadow, bool file, int *memcgid,
+               struct pglist_data **pgdat, unsigned long *token, bool *workingset)
+{
+       return false;
+}
+
 static void lru_gen_refault(struct folio *folio, void *shadow)
 {
 }

@@ -373,40 +402,31 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
                                folio_test_workingset(folio));
 }

-/**
- * workingset_refault - Evaluate the refault of a previously evicted folio.
- * @folio: The freshly allocated replacement folio.
- * @shadow: Shadow entry of the evicted folio.
+/*
+ * Test if the folio is recently evicted by checking if
+ * refault distance of shadow exceeds workingset size.
  *
- * Calculates and evaluates the refault distance of the previously
- * evicted folio in the context of the node and the memcg whose memory
- * pressure caused the eviction.
+ * As a side effect, populate workingset with the value
+ * unpacked from shadow.
  */
-void workingset_refault(struct folio *folio, void *shadow)
+bool workingset_test_recent(void *shadow, bool file, bool *workingset)
 {
-       bool file = folio_is_file_lru(folio);
        struct mem_cgroup *eviction_memcg;
        struct lruvec *eviction_lruvec;
        unsigned long refault_distance;
        unsigned long workingset_size;
-       struct pglist_data *pgdat;
-       struct mem_cgroup *memcg;
-       unsigned long eviction;
-       struct lruvec *lruvec;
        unsigned long refault;
-       bool workingset;
        int memcgid;
-       long nr;
+       struct pglist_data *pgdat;
+       unsigned long eviction;

-       if (lru_gen_enabled()) {
-               lru_gen_refault(folio, shadow);
-               return;
-       }
+       if (lru_gen_enabled())
+               lru_gen_test_recent(shadow, file, &memcgid, &pgdat, &eviction,
+                       workingset);

Missing "return", which was correctly handled in your v2, btw.

Oops copy-paste hazard. I'll fix this...