@@ -133,31 +133,25 @@ static inline int lru_hist_from_seq(unsigned long seq)
return seq % NR_HIST_GENS;
}
-static inline int lru_tier_from_refs(int refs)
+static inline int lru_tier_from_refs(int refs, bool workingset)
{
VM_WARN_ON_ONCE(refs > BIT(LRU_REFS_WIDTH));
- /* see the comment in folio_lru_refs() */
- return order_base_2(refs + 1);
+ /* see the comment on MAX_NR_TIERS */
+ return workingset ? MAX_NR_TIERS - 1 : order_base_2(refs);
}
static inline int folio_lru_refs(struct folio *folio)
{
unsigned long flags = READ_ONCE(folio->flags);
- bool workingset = flags & BIT(PG_workingset);
+ if (!(flags & BIT(PG_referenced)))
+ return 0;
/*
- * Return the number of accesses beyond PG_referenced, i.e., N-1 if the
- * total number of accesses is N>1, since N=0,1 both map to the first
- * tier. lru_tier_from_refs() will account for this off-by-one. Also see
- * the comment on MAX_NR_TIERS.
+ * Return the total number of accesses including PG_referenced. Also see
+ * the comment on LRU_REFS_FLAGS.
*/
- return ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + workingset;
-}
-
-static inline void folio_clear_lru_refs(struct folio *folio)
-{
- set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS, 0);
+ return ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1;
}
static inline int folio_lru_gen(struct folio *folio)
@@ -223,11 +217,46 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli
VM_WARN_ON_ONCE(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen));
}
+static inline int lru_gen_distance(struct folio *folio, bool reclaiming)
+{
+ /*
+ * Distance until eviction (larger values provide stronger protection):
+ * +-------------------------------------+-------------------------------------+
+ * | Accessed through page tables and | Accessed through file descriptors |
+ * | promoted by folio_update_gen() | and protected by folio_inc_gen() |
+ * +-------------------------------------+-------------------------------------+
+ * | PG_active (only set while isolated) | |
+ * +------------------+------------------+------------------+------------------+
+ * | PG_workingset | PG_referenced | PG_workingset | LRU_REFS_FLAGS |
+ * +-------------------------------------+-------------------------------------+
+ * | 3 | 2 | 1 | 0 |
+ * +-------------------------------------+-------------------------------------+
+ * |<----------- MIN_NR_GENS ----------->| |
+ * |<------------------------------ MAX_NR_GENS ------------------------------>|
+ */
+ if (reclaiming)
+ return 0;
+
+ if (folio_test_active(folio))
+ return MIN_NR_GENS + folio_test_workingset(folio);
+
+ if (folio_test_workingset(folio))
+ return MIN_NR_GENS - 1;
+
+ if (!folio_is_file_lru(folio) && !folio_test_swapcache(folio))
+ return MIN_NR_GENS - 1;
+
+ if (folio_test_reclaim(folio) && (folio_test_dirty(folio) || folio_test_writeback(folio)))
+ return MIN_NR_GENS - 1;
+
+ return 0;
+}
+
static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
{
+ int dist;
unsigned long seq;
unsigned long flags;
- unsigned long mask;
int gen = folio_lru_gen(folio);
int type = folio_is_file_lru(folio);
int zone = folio_zonenum(folio);
@@ -237,40 +266,17 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
if (folio_test_unevictable(folio) || !lrugen->enabled)
return false;
- /*
- * There are four common cases for this page:
- * 1. If it's hot, i.e., freshly faulted in, add it to the youngest
- * generation, and it's protected over the rest below.
- * 2. If it can't be evicted immediately, i.e., a dirty page pending
- * writeback, add it to the second youngest generation.
- * 3. If it should be evicted first, e.g., cold and clean from
- * folio_rotate_reclaimable(), add it to the oldest generation.
- * 4. Everything else falls between 2 & 3 above and is added to the
- * second oldest generation if it's considered inactive, or the
- * oldest generation otherwise. See lru_gen_is_active().
- */
- if (folio_test_active(folio))
- seq = lrugen->max_seq;
- else if ((type == LRU_GEN_ANON && !folio_test_swapcache(folio)) ||
- (folio_test_reclaim(folio) &&
- (folio_test_dirty(folio) || folio_test_writeback(folio))))
- seq = lrugen->max_seq - 1;
- else if (reclaiming || lrugen->min_seq[type] + MIN_NR_GENS >= lrugen->max_seq)
- seq = lrugen->min_seq[type];
+
+ dist = lru_gen_distance(folio, reclaiming);
+ if (dist < MIN_NR_GENS)
+ seq = lrugen->min_seq[type] + dist;
else
- seq = lrugen->min_seq[type] + 1;
+ seq = lrugen->max_seq + dist - MIN_NR_GENS - 1;
gen = lru_gen_from_seq(seq);
flags = (gen + 1UL) << LRU_GEN_PGOFF;
/* see the comment on MIN_NR_GENS about PG_active */
- mask = LRU_GEN_MASK;
- /*
- * Don't clear PG_workingset here because it can affect PSI accounting
- * if the activation is due to workingset refault.
- */
- if (folio_test_active(folio))
- mask |= LRU_REFS_MASK | BIT(PG_referenced) | BIT(PG_active);
- set_mask_bits(&folio->flags, mask, flags);
+ set_mask_bits(&folio->flags, LRU_GEN_MASK | BIT(PG_active), flags);
lru_gen_update_size(lruvec, folio, -1, gen);
/* for folio_rotate_reclaimable() */
@@ -332,66 +332,88 @@ enum lruvec_flags {
#endif /* !__GENERATING_BOUNDS_H */
/*
- * Evictable pages are divided into multiple generations. The youngest and the
+ * Evictable folios are divided into multiple generations. The youngest and the
* oldest generation numbers, max_seq and min_seq, are monotonically increasing.
* They form a sliding window of a variable size [MIN_NR_GENS, MAX_NR_GENS]. An
* offset within MAX_NR_GENS, i.e., gen, indexes the LRU list of the
* corresponding generation. The gen counter in folio->flags stores gen+1 while
- * a page is on one of lrugen->folios[]. Otherwise it stores 0.
+ * a folio is on one of lrugen->folios[]. Otherwise it stores 0.
*
- * A page is added to the youngest generation on faulting. The aging needs to
- * check the accessed bit at least twice before handing this page over to the
- * eviction. The first check takes care of the accessed bit set on the initial
- * fault; the second check makes sure this page hasn't been used since then.
- * This process, AKA second chance, requires a minimum of two generations,
- * hence MIN_NR_GENS. And to maintain ABI compatibility with the active/inactive
- * LRU, e.g., /proc/vmstat, these two generations are considered active; the
- * rest of generations, if they exist, are considered inactive. See
- * lru_gen_is_active().
+ * After a folio is faulted in, the aging needs to check the accessed bit at
+ * least twice before handing this folio over to the eviction. The first check
+ * clears the accessed bit from the initial fault; the second check makes sure
+ * this folio hasn't been used since then. This process, AKA second chance,
+ * requires a minimum of two generations, hence MIN_NR_GENS. And to maintain ABI
+ * compatibility with the active/inactive LRU, e.g., /proc/vmstat, these two
+ * generations are considered active; the rest of generations, if they exist,
+ * are considered inactive. See lru_gen_is_active().
*
- * PG_active is always cleared while a page is on one of lrugen->folios[] so
- * that the aging needs not to worry about it. And it's set again when a page
- * considered active is isolated for non-reclaiming purposes, e.g., migration.
- * See lru_gen_add_folio() and lru_gen_del_folio().
+ * PG_active is always cleared while a folio is on one of lrugen->folios[] so
+ * that the sliding window needs not to worry about it. And it's set again when
+ * a folio considered active is isolated for non-reclaiming purposes, e.g.,
+ * migration. See lru_gen_add_folio() and lru_gen_del_folio().
*
* MAX_NR_GENS is set to 4 so that the multi-gen LRU can support twice the
* number of categories of the active/inactive LRU when keeping track of
* accesses through page tables. This requires order_base_2(MAX_NR_GENS+1) bits
- * in folio->flags.
+ * in folio->flags, masked by LRU_GEN_MASK.
*/
#define MIN_NR_GENS 2U
#define MAX_NR_GENS 4U
/*
- * Each generation is divided into multiple tiers. A page accessed N times
- * through file descriptors is in tier order_base_2(N). A page in the first tier
- * (N=0,1) is marked by PG_referenced unless it was faulted in through page
- * tables or read ahead. A page in any other tier (N>1) is marked by
- * PG_referenced and PG_workingset. This implies a minimum of two tiers is
- * supported without using additional bits in folio->flags.
+ * Each generation is divided into multiple tiers. A folio accessed N times
+ * through file descriptors is in tier order_base_2(N). A folio in the first
+ * tier (N=0,1) is marked by PG_referenced unless it was faulted in through page
+ * tables or read ahead. A folio in the last tier (MAX_NR_TIERS-1) is marked by
+ * PG_workingset. A folio in any other tier (1<N<5) between the first and last
+ * is marked by additional bits of LRU_REFS_WIDTH in folio->flags.
*
* In contrast to moving across generations which requires the LRU lock, moving
* across tiers only involves atomic operations on folio->flags and therefore
* has a negligible cost in the buffered access path. In the eviction path,
- * comparisons of refaulted/(evicted+protected) from the first tier and the
- * rest infer whether pages accessed multiple times through file descriptors
- * are statistically hot and thus worth protecting.
+ * comparisons of refaulted/(evicted+protected) from the first tier and the rest
+ * infer whether folios accessed multiple times through file descriptors are
+ * statistically hot and thus worth protecting.
*
* MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice the
* number of categories of the active/inactive LRU when keeping track of
* accesses through file descriptors. This uses MAX_NR_TIERS-2 spare bits in
- * folio->flags.
+ * folio->flags, masked by LRU_REFS_MASK.
*/
#define MAX_NR_TIERS 4U
#ifndef __GENERATING_BOUNDS_H
-struct lruvec;
-struct page_vma_mapped_walk;
-
#define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
#define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF)
+/*
+ * For folios accessed multiple times through file descriptors,
+ * lru_gen_inc_refs() sets additional bits of LRU_REFS_WIDTH in folio->flags
+ * after PG_referenced, then PG_workingset after LRU_REFS_WIDTH. After all its
+ * bits are set, i.e., LRU_REFS_FLAGS|BIT(PG_workingset), a folio is lazily
+ * promoted into the second oldest generation in the eviction path. And when
+ * folio_inc_gen() does that, it clears LRU_REFS_FLAGS so that
+ * lru_gen_inc_refs() can start over. Note that for this case, LRU_REFS_MASK is
+ * only valid when PG_referenced is set.
+ *
+ * For folios accessed multiple times through page tables, folio_update_gen()
+ * from a page table walk or lru_gen_set_refs() from a rmap walk sets
+ * PG_referenced after the accessed bit is cleared for the first time.
+ * Thereafter, those two paths set PG_workingset and promote folios to the
+ * youngest generation. Like folio_inc_gen(), folio_update_gen() also clears
+ * PG_referenced. Note that for this case, LRU_REFS_MASK is not used.
+ *
+ * For both cases above, after PG_workingset is set on a folio, it remains until
+ * this folio is either reclaimed, or "deactivated" by lru_gen_clear_refs(). It
+ * can be set again if lru_gen_test_recent() returns true upon a refault.
+ */
+#define LRU_REFS_FLAGS (LRU_REFS_MASK | BIT(PG_referenced))
+
+struct lruvec;
+struct page_vma_mapped_walk;
+
#ifdef CONFIG_LRU_GEN
enum {
@@ -406,8 +428,6 @@ enum {
NR_LRU_GEN_CAPS
};
-#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset))
-
#define MIN_LRU_BATCH BITS_PER_LONG
#define MAX_LRU_BATCH (MIN_LRU_BATCH * 64)
@@ -387,24 +387,19 @@ static void lru_gen_inc_refs(struct folio *folio)
if (!folio_test_lru(folio) || folio_test_unevictable(folio))
return;
+ /* see the comment on LRU_REFS_FLAGS */
if (!folio_test_referenced(folio)) {
- folio_set_referenced(folio);
+ set_mask_bits(&folio->flags, LRU_REFS_MASK, BIT(PG_referenced));
return;
}
- if (!folio_test_workingset(folio)) {
- folio_set_workingset(folio);
- return;
- }
-
- /* see the comment on MAX_NR_TIERS */
do {
- new_flags = old_flags & LRU_REFS_MASK;
- if (new_flags == LRU_REFS_MASK)
- break;
+ if ((old_flags & LRU_REFS_MASK) == LRU_REFS_MASK) {
+ folio_set_workingset(folio);
+ return;
+ }
- new_flags += BIT(LRU_REFS_PGOFF);
- new_flags |= old_flags & ~LRU_REFS_MASK;
+ new_flags = old_flags + BIT(LRU_REFS_PGOFF);
} while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
}
@@ -416,7 +411,7 @@ static bool lru_gen_clear_refs(struct folio *folio)
if (!folio_test_lru(folio) || folio_test_unevictable(folio))
return true;
- set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS, 0);
+ set_mask_bits(&folio->flags, LRU_REFS_FLAGS | BIT(PG_workingset), 0);
lrugen = &folio_lruvec(folio)->lrugen;
/* whether can do without shuffling under the LRU lock */
@@ -498,7 +493,7 @@ void folio_add_lru(struct folio *folio)
folio_test_unevictable(folio), folio);
VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
- /* see the comment in lru_gen_add_folio() */
+ /* see the comment in lru_gen_distance() */
if (lru_gen_enabled() && !folio_test_unevictable(folio) &&
lru_gen_in_fault() && !(current->flags & PF_MEMALLOC))
folio_set_active(folio);
@@ -862,6 +862,31 @@ enum folio_references {
FOLIOREF_ACTIVATE,
};
+#ifdef CONFIG_LRU_GEN
+/*
+ * Only used on a mapped folio in the eviction (rmap walk) path, where promotion
+ * needs to be done by taking the folio off the LRU list and then adding it back
+ * with PG_active set. In contrast, the aging (page table walk) path uses
+ * folio_update_gen().
+ */
+static bool lru_gen_set_refs(struct folio *folio)
+{
+ /* see the comment on LRU_REFS_FLAGS */
+ if (!folio_test_referenced(folio) && !folio_test_workingset(folio)) {
+ set_mask_bits(&folio->flags, LRU_REFS_MASK, BIT(PG_referenced));
+ return false;
+ }
+
+ set_mask_bits(&folio->flags, LRU_REFS_FLAGS, BIT(PG_workingset));
+ return true;
+}
+#else
+static bool lru_gen_set_refs(struct folio *folio)
+{
+ return false;
+}
+#endif /* CONFIG_LRU_GEN */
+
static enum folio_references folio_check_references(struct folio *folio,
struct scan_control *sc)
{
@@ -870,7 +895,6 @@ static enum folio_references folio_check_references(struct folio *folio,
referenced_ptes = folio_referenced(folio, 1, sc->target_mem_cgroup,
&vm_flags);
- referenced_folio = folio_test_clear_referenced(folio);
/*
* The supposedly reclaimable folio was found to be in a VM_LOCKED vma.
@@ -888,6 +912,15 @@ static enum folio_references folio_check_references(struct folio *folio,
if (referenced_ptes == -1)
return FOLIOREF_KEEP;
+ if (lru_gen_enabled()) {
+ if (!referenced_ptes)
+ return FOLIOREF_RECLAIM;
+
+ return lru_gen_set_refs(folio) ? FOLIOREF_ACTIVATE : FOLIOREF_KEEP;
+ }
+
+ referenced_folio = folio_test_clear_referenced(folio);
+
if (referenced_ptes) {
/*
* All mapped folios start out with page table
@@ -1092,11 +1125,6 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
if (!sc->may_unmap && folio_mapped(folio))
goto keep_locked;
- /* folio_update_gen() tried to promote this page? */
- if (lru_gen_enabled() && !ignore_references &&
- folio_mapped(folio) && folio_test_referenced(folio))
- goto keep_locked;
-
/*
* The number of dirty pages determines if a node is marked
* reclaim_congested. kswapd will stall and start writing
@@ -3163,16 +3191,19 @@ static int folio_update_gen(struct folio *folio, int gen)
VM_WARN_ON_ONCE(gen >= MAX_NR_GENS);
+ /* see the comment on LRU_REFS_FLAGS */
+ if (!folio_test_referenced(folio) && !folio_test_workingset(folio)) {
+ set_mask_bits(&folio->flags, LRU_REFS_MASK, BIT(PG_referenced));
+ return -1;
+ }
+
do {
/* lru_gen_del_folio() has isolated this page? */
- if (!(old_flags & LRU_GEN_MASK)) {
- /* for shrink_folio_list() */
- new_flags = old_flags | BIT(PG_referenced);
- continue;
- }
+ if (!(old_flags & LRU_GEN_MASK))
+ return -1;
- new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_MASK | LRU_REFS_FLAGS);
- new_flags |= (gen + 1UL) << LRU_GEN_PGOFF;
+ new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_FLAGS);
+ new_flags |= ((gen + 1UL) << LRU_GEN_PGOFF) | BIT(PG_workingset);
} while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
return ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
@@ -3196,7 +3227,7 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclai
new_gen = (old_gen + 1) % MAX_NR_GENS;
- new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_MASK | LRU_REFS_FLAGS);
+ new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_FLAGS);
new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
/* for folio_end_writeback() */
if (reclaiming)
@@ -3374,9 +3405,11 @@ static unsigned long get_pmd_pfn(pmd_t pmd, struct vm_area_struct *vma, unsigned
static struct folio *get_pfn_folio(unsigned long pfn, struct mem_cgroup *memcg,
struct pglist_data *pgdat)
{
- struct folio *folio;
+ struct folio *folio = pfn_folio(pfn);
+
+ if (folio_lru_gen(folio) < 0)
+ return NULL;
- folio = pfn_folio(pfn);
if (folio_nid(folio) != pgdat->node_id)
return NULL;
@@ -3753,8 +3786,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
while (!list_empty(head)) {
struct folio *folio = lru_to_folio(head);
int refs = folio_lru_refs(folio);
- int tier = lru_tier_from_refs(refs);
- int delta = folio_nr_pages(folio);
+ bool workingset = folio_test_workingset(folio);
VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
@@ -3764,8 +3796,14 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
new_gen = folio_inc_gen(lruvec, folio, false);
list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
- WRITE_ONCE(lrugen->protected[hist][type][tier],
- lrugen->protected[hist][type][tier] + delta);
+ /* don't count the workingset being lazily promoted */
+ if (refs + workingset != BIT(LRU_REFS_WIDTH) + 1) {
+ int tier = lru_tier_from_refs(refs, workingset);
+ int delta = folio_nr_pages(folio);
+
+ WRITE_ONCE(lrugen->protected[hist][type][tier],
+ lrugen->protected[hist][type][tier] + delta);
+ }
if (!--remaining)
return false;
@@ -4134,16 +4172,10 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
old_gen = folio_update_gen(folio, new_gen);
if (old_gen >= 0 && old_gen != new_gen)
update_batch_size(walk, folio, old_gen, new_gen);
-
- continue;
- }
-
- old_gen = folio_lru_gen(folio);
- if (old_gen < 0)
- folio_set_referenced(folio);
- else if (old_gen != new_gen) {
- folio_clear_lru_refs(folio);
- folio_activate(folio);
+ } else if (lru_gen_set_refs(folio)) {
+ old_gen = folio_lru_gen(folio);
+ if (old_gen >= 0 && old_gen != new_gen)
+ folio_activate(folio);
}
}
@@ -4304,7 +4336,8 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
int zone = folio_zonenum(folio);
int delta = folio_nr_pages(folio);
int refs = folio_lru_refs(folio);
- int tier = lru_tier_from_refs(refs);
+ bool workingset = folio_test_workingset(folio);
+ int tier = lru_tier_from_refs(refs, workingset);
struct lru_gen_folio *lrugen = &lruvec->lrugen;
VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
@@ -4326,14 +4359,17 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
}
/* protected */
- if (tier > tier_idx || refs == BIT(LRU_REFS_WIDTH)) {
- int hist = lru_hist_from_seq(lrugen->min_seq[type]);
-
+ if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) {
gen = folio_inc_gen(lruvec, folio, false);
- list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
+ list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
- WRITE_ONCE(lrugen->protected[hist][type][tier],
- lrugen->protected[hist][type][tier] + delta);
+ /* don't count the workingset being lazily promoted */
+ if (refs + workingset != BIT(LRU_REFS_WIDTH) + 1) {
+ int hist = lru_hist_from_seq(lrugen->min_seq[type]);
+
+ WRITE_ONCE(lrugen->protected[hist][type][tier],
+ lrugen->protected[hist][type][tier] + delta);
+ }
return true;
}
@@ -4353,8 +4389,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
}
/* waiting for writeback */
- if (folio_test_locked(folio) || writeback ||
- (type == LRU_GEN_FILE && dirty)) {
+ if (writeback || (type == LRU_GEN_FILE && dirty)) {
gen = folio_inc_gen(lruvec, folio, true);
list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
return true;
@@ -4383,13 +4418,12 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
return false;
}
- /* see the comment on MAX_NR_TIERS */
+ /* see the comment on LRU_REFS_FLAGS */
if (!folio_test_referenced(folio))
- folio_clear_lru_refs(folio);
+ set_mask_bits(&folio->flags, LRU_REFS_MASK, 0);
/* for shrink_folio_list() */
folio_clear_reclaim(folio);
- folio_clear_referenced(folio);
success = lru_gen_del_folio(lruvec, folio, true);
VM_WARN_ON_ONCE_FOLIO(!success, folio);
@@ -4585,25 +4619,16 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
continue;
}
- if (folio_test_reclaim(folio) &&
- (folio_test_dirty(folio) || folio_test_writeback(folio))) {
- /* restore LRU_REFS_FLAGS cleared by isolate_folio() */
- if (folio_test_workingset(folio))
- folio_set_referenced(folio);
- continue;
- }
-
- if (skip_retry || folio_test_active(folio) || folio_test_referenced(folio) ||
- folio_mapped(folio) || folio_test_locked(folio) ||
- folio_test_dirty(folio) || folio_test_writeback(folio)) {
- /* don't add rejected folios to the oldest generation */
- set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS,
- BIT(PG_active));
- continue;
- }
-
/* retry folios that may have missed folio_rotate_reclaimable() */
- list_move(&folio->lru, &clean);
+ if (!skip_retry && !folio_test_active(folio) && !folio_mapped(folio) &&
+ !folio_test_dirty(folio) && !folio_test_writeback(folio)) {
+ list_move(&folio->lru, &clean);
+ continue;
+ }
+
+ /* don't add rejected folios to the oldest generation */
+ if (!lru_gen_distance(folio, false))
+ set_mask_bits(&folio->flags, LRU_REFS_FLAGS, BIT(PG_active));
}
spin_lock_irq(&lruvec->lru_lock);
@@ -239,7 +239,8 @@ static void *lru_gen_eviction(struct folio *folio)
int type = folio_is_file_lru(folio);
int delta = folio_nr_pages(folio);
int refs = folio_lru_refs(folio);
- int tier = lru_tier_from_refs(refs);
+ bool workingset = folio_test_workingset(folio);
+ int tier = lru_tier_from_refs(refs, workingset);
struct mem_cgroup *memcg = folio_memcg(folio);
struct pglist_data *pgdat = folio_pgdat(folio);
@@ -253,7 +254,7 @@ static void *lru_gen_eviction(struct folio *folio)
hist = lru_hist_from_seq(min_seq);
atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
- return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
+ return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset);
}
/*
@@ -304,24 +305,20 @@ static void lru_gen_refault(struct folio *folio, void *shadow)
lrugen = &lruvec->lrugen;
hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type]));
- /* see the comment in folio_lru_refs() */
- refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset;
- tier = lru_tier_from_refs(refs);
+ refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + 1;
+ tier = lru_tier_from_refs(refs, workingset);
atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
- mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
- /*
- * Count the following two cases as stalls:
- * 1. For pages accessed through page tables, hotter pages pushed out
- * hot pages which refaulted immediately.
- * 2. For pages accessed multiple times through file descriptors,
- * they would have been protected by sort_folio().
- */
- if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) {
- set_mask_bits(&folio->flags, 0, LRU_REFS_MASK | BIT(PG_workingset));
+ /* see folio_add_lru() where folio_set_active() happens */
+ if (lru_gen_in_fault())
+ mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
+
+ if (workingset) {
+ folio_set_workingset(folio);
mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
- }
+ } else
+ set_mask_bits(&folio->flags, LRU_REFS_MASK, (refs - 1UL) << LRU_REFS_PGOFF);
unlock:
rcu_read_unlock();
}
With the aging feedback no longer considering the distribution of folios in each generation, rework workingset protection to better distribute folios across MAX_NR_GENS. This is achieved by reusing PG_workingset and PG_referenced/LRU_REFS_FLAGS in a slightly different way. For folios accessed multiple times through file descriptors, make lru_gen_inc_refs() set additional bits of LRU_REFS_WIDTH in folio->flags after PG_referenced, then PG_workingset after LRU_REFS_WIDTH. After all its bits are set, i.e., LRU_REFS_FLAGS|BIT(PG_workingset), a folio is lazily promoted into the second oldest generation in the eviction path. And when folio_inc_gen() does that, it clears LRU_REFS_FLAGS so that lru_gen_inc_refs() can start over. For this case, LRU_REFS_MASK is only valid when PG_referenced is set. For folios accessed multiple times through page tables, folio_update_gen() from a page table walk or lru_gen_set_refs() from a rmap walk sets PG_referenced after the accessed bit is cleared for the first time. Thereafter, those two paths set PG_workingset and promote folios to the youngest generation. Like folio_inc_gen(), when folio_update_gen() does that, it also clears PG_referenced. For this case, LRU_REFS_MASK is not used. For both of the cases, after PG_workingset is set on a folio, it remains until this folio is either reclaimed, or "deactivated" by lru_gen_clear_refs(). It can be set again if lru_gen_test_recent() returns true upon a refault. When adding folios to the LRU lists, lru_gen_distance() distributes them as follows: +---------------------------------+---------------------------------+ | Accessed thru page tables | Accessed thru file descriptors | +---------------------------------+---------------------------------+ | PG_active (set while isolated) | | +----------------+----------------+----------------+----------------+ | PG_workingset | PG_referenced | PG_workingset | LRU_REFS_FLAGS | +---------------------------------+---------------------------------+ |<--------- MIN_NR_GENS --------->| | |<-------------------------- MAX_NR_GENS -------------------------->| After this patch, some typical client and server workloads showed improvements under heavy memory pressure. For example, Python TPC-C, which was used to benchmark a different approach [1] to better detect refault distances, showed a significant decrease in total refaults: Before After Change Time (seconds) 10801 10801 0% Executed (transactions) 41472 43663 +5% workingset_nodes 109070 120244 +10% workingset_refault_anon 5019627 7281831 +45% workingset_refault_file 1294678786 554855564 -57% workingset_refault_total 1299698413 562137395 -57% [1] https://lore.kernel.org/20230920190244.16839-1-ryncsn@gmail.com/ Reported-by: Kairui Song <kasong@tencent.com> Closes: https://lore.kernel.org/CAOUHufahuWcKf5f1Sg3emnqX+cODuR=2TQo7T4Gr-QYLujn4RA@mail.gmail.com/ Signed-off-by: Yu Zhao <yuzhao@google.com> Tested-by: Kalesh Singh <kaleshsingh@google.com> --- include/linux/mm_inline.h | 94 ++++++++++++------------ include/linux/mmzone.h | 82 +++++++++++++-------- mm/swap.c | 23 +++--- mm/vmscan.c | 145 ++++++++++++++++++++++---------------- mm/workingset.c | 29 ++++---- 5 files changed, 208 insertions(+), 165 deletions(-)