[PATCH v6 15/15] mm/mglru: Avoid scan anon while swapcache is low for GFP_NOIO allocation
From: Barry Song (Xiaomi)
Date: Tue Nov 10 2026 - 17:23:48 EST
From: Bo Zhang <zhangbo56@xxxxxxxxxx>
With GFP_NOIO, we cannot reclaim anon folios unless they are in
the swap cache. CLRU skips anon reclaim when the swap cache is
very low by commit 74d9aa0d8e98 ("mm: vmscan: avoid anon scanning
for GFP_NOIO with low swapcache"). Apply the same logic to MGLRU.
The new scan-budget-based mechanism makes this straightforward to
implement. Thanks also to Xiang Liu, who previously attempted to fix
this before we had the scan-budget-based model [1].
[1] https://lore.kernel.org/linux-mm/179248830836.1744016.8424217811286616919.noio-mglru-rfc-v2@xxxxxxxxxxxxx/
Cc: Xiang Liu <liuxiang.277@xxxxxxxxxxxxx>
Signed-off-by: Bo Zhang <zhangbo56@xxxxxxxxxx>
Co-developed-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
Reviewed-by: Kunwu Chan <chentao@xxxxxxxxxx>
---
mm/vmscan.c | 44 ++++++++++++++++++++++----------------------
1 file changed, 22 insertions(+), 22 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 379339220878..fa0245a07caa 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -272,13 +272,6 @@ static inline bool reclaimable_anon_is_low(struct mem_cgroup *memcg,
if (!sc || (sc->gfp_mask & __GFP_IO))
return false;
- /*
- * FIXME: MGLRU doesn't fully respect can_reclaim_anon_pages() for the
- * scanning type, so only apply this to the traditional LRU for now.
- */
- if (lru_gen_enabled())
- return false;
-
if (memcg) {
struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
@@ -4206,12 +4199,14 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
}
-static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
- unsigned long nr[])
+static void lruvec_evictable_size(struct lruvec *lruvec, struct scan_control *sc,
+ int swappiness, unsigned long nr[])
{
int type;
unsigned long seq;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+ int nid = lruvec_pgdat(lruvec)->node_id;
DEFINE_MAX_SEQ(lruvec);
DEFINE_MIN_SEQ(lruvec);
@@ -4219,6 +4214,8 @@ static void lruvec_evictable_size(struct lruvec *lruvec, int swappiness,
nr[LRU_GEN_FILE] = 0;
for_each_evictable_type(type, swappiness) {
+ if (type == LRU_GEN_ANON && !can_reclaim_anon_pages(memcg, nid, sc))
+ continue;
for (seq = min_seq[type]; seq <= max_seq; seq++)
nr[type] += lruvec_gen_size(lrugen, type, seq, sc->reclaim_idx + 1);
}
@@ -4229,7 +4226,7 @@ static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
unsigned long total, sizes[ANON_AND_FILE];
int swappiness = get_swappiness(lruvec, sc);
- lruvec_evictable_size(lruvec, swappiness, sizes);
+ lruvec_evictable_size(lruvec, sc, swappiness, sizes);
total = sizes[LRU_GEN_ANON] + sizes[LRU_GEN_FILE];
/* whether the size is big enough to be helpful */
@@ -4893,23 +4890,19 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
{
struct lru_gen_folio *lrugen = &lruvec->lrugen;
u64 refault_rate[ANON_AND_FILE], anon_factor, file_factor;
- u64 anon_scan, file_scan, total;
+ u64 anon_scan, file_scan;
u64 anon_weight, file_weight;
int size_bias;
- total = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE];
- if (!total)
- return;
-
- if (swappiness <= MIN_SWAPPINESS) {
+ if (swappiness <= MIN_SWAPPINESS)
nr[LRU_GEN_ANON] = 0;
- nr[LRU_GEN_FILE] = min_t(u64, total_scan, nr[LRU_GEN_FILE]);
- return;
- }
- if (swappiness == SWAPPINESS_ANON_ONLY) {
+ if (swappiness == SWAPPINESS_ANON_ONLY)
nr[LRU_GEN_FILE] = 0;
+
+ if (!nr[LRU_GEN_ANON] || !nr[LRU_GEN_FILE]) {
nr[LRU_GEN_ANON] = min_t(u64, total_scan, nr[LRU_GEN_ANON]);
+ nr[LRU_GEN_FILE] = min_t(u64, total_scan, nr[LRU_GEN_FILE]);
return;
}
@@ -5113,12 +5106,19 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
struct scan_control *sc, int swappiness,
bool do_balance)
{
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MIN_SEQ(lruvec);
/* have to run aging, since eviction is not possible anymore */
if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
return true;
+ /* run aging when GFP_NOIO limits anon reclaim with few swapcache folios */
+ if (swappiness && min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq &&
+ reclaimable_anon_is_low(memcg, pgdat->node_id, sc))
+ return true;
+
/* try to avoid aging, do gentle reclaim at the default priority */
if (sc->priority == DEF_PRIORITY)
return false;
@@ -5137,7 +5137,7 @@ static void lru_gen_prepare_scan(struct lruvec *lruvec, struct scan_control *sc,
{
unsigned long total;
- lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+ lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
total = nr_to_scan[LRU_GEN_ANON] + nr_to_scan[LRU_GEN_FILE];
/* Just scrape all pages calculated above if this memcg was deleted */
@@ -5888,7 +5888,7 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
if (sc->nr_reclaimed >= nr_to_reclaim)
return 0;
- lruvec_evictable_size(lruvec, swappiness, nr_to_scan);
+ lruvec_evictable_size(lruvec, sc, swappiness, nr_to_scan);
lru_gen_balance_scan(lruvec, sc, swappiness,
nr_to_reclaim - sc->nr_reclaimed, nr_to_scan);
--
2.34.1