[v10,1/3] workingset: refactor LRU refault to expose refault recency check
Commit Message
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(-)
--
2.39.1
Comments
On Sat, Feb 18, 2023 at 11:33:16PM -0800, Nhat Pham wrote:
> +++ 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.
> + */
I find this comment hard to understand. First it talks about "the
folio", but it doesn't pass a folio. Then it talks about "the
references", but I don't have any idea what those are either.
I think what you mean is,
* Test if the shadow entry is for a folio which was recently evicted.
* Fills in @memcgid, @pgdat, @token and @workingset with values
* extracted from the shadow entry.
> +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));
> +}
[...]
> +/*
> + * 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.
> */
1. Shouldn't this be kernel-doc?
2. Again, don't use the term "side effect" here. It's just one of
the things that the function _does_.
On Sun, Feb 19, 2023 at 4:05 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sat, Feb 18, 2023 at 11:33:16PM -0800, Nhat Pham wrote:
> > +++ 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.
> > + */
>
> I find this comment hard to understand. First it talks about "the
> folio", but it doesn't pass a folio. Then it talks about "the
> references", but I don't have any idea what those are either.
>
> I think what you mean is,
>
> * Test if the shadow entry is for a folio which was recently evicted.
> * Fills in @memcgid, @pgdat, @token and @workingset with values
> * extracted from the shadow entry.
I'll fix this comment in the next version. Thanks for the suggestion!
>
> > +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));
> > +}
>
> [...]
>
> > +/*
> > + * 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.
> > */
>
> 1. Shouldn't this be kernel-doc?
Hmm good point...
> 2. Again, don't use the term "side effect" here. It's just one of
> the things that the function _does_.
>
I'll fix this! Thanks for pointing it out.
@@ -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);
@@ -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())
+ return lru_gen_test_recent(shadow, file, &memcgid, &pgdat, &eviction,
+ workingset);
- unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
+ unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
eviction <<= bucket_order;
- rcu_read_lock();
/*
* Look up the memcg associated with the stored ID. It might
* have been deleted since the folio's eviction.
@@ -425,7 +445,8 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
eviction_memcg = mem_cgroup_from_id(memcgid);
if (!mem_cgroup_disabled() && !eviction_memcg)
- goto out;
+ return false;
+
eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
refault = atomic_long_read(&eviction_lruvec->nonresident_age);
@@ -447,21 +468,6 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
refault_distance = (refault - eviction) & EVICTION_MASK;
- /*
- * The activation decision for this folio is made at the level
- * where the eviction occurred, as that is where the LRU order
- * during folio reclaim is being determined.
- *
- * However, the cgroup that will own the folio is the one that
- * is actually experiencing the refault event.
- */
- nr = folio_nr_pages(folio);
- memcg = folio_memcg(folio);
- pgdat = folio_pgdat(folio);
- lruvec = mem_cgroup_lruvec(memcg, pgdat);
-
- mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
-
mem_cgroup_flush_stats_delayed();
/*
* Compare the distance to the existing workingset size. We
@@ -483,7 +489,51 @@ void workingset_refault(struct folio *folio, void *shadow)
NR_INACTIVE_ANON);
}
}
- if (refault_distance > workingset_size)
+
+ return refault_distance <= workingset_size;
+}
+
+/**
+ * workingset_refault - Evaluate the refault of a previously evicted folio.
+ * @folio: The freshly allocated replacement folio.
+ * @shadow: Shadow entry of the evicted folio.
+ *
+ * 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.
+ */
+void workingset_refault(struct folio *folio, void *shadow)
+{
+ bool file = folio_is_file_lru(folio);
+ struct pglist_data *pgdat;
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+ bool workingset;
+ long nr;
+
+ if (lru_gen_enabled()) {
+ lru_gen_refault(folio, shadow);
+ return;
+ }
+
+ rcu_read_lock();
+
+ /*
+ * The activation decision for this folio is made at the level
+ * where the eviction occurred, as that is where the LRU order
+ * during folio reclaim is being determined.
+ *
+ * However, the cgroup that will own the folio is the one that
+ * is actually experiencing the refault event.
+ */
+ nr = folio_nr_pages(folio);
+ memcg = folio_memcg(folio);
+ pgdat = folio_pgdat(folio);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+ mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
+
+ if (!workingset_test_recent(shadow, file, &workingset))
goto out;
folio_set_active(folio);