The patch titled
Subject: mm: multi-gen LRU: clarify scan_control flags
has been added to the -mm mm-unstable branch. Its filename is
mm-multi-gen-lru-clarify-scan_control-flags.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-multi-gen-lru-clarify-scan_control-flags.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yu Zhao <yuzhao@xxxxxxxxxx>
Subject: mm: multi-gen LRU: clarify scan_control flags
Date: Wed, 21 Dec 2022 21:19:05 -0700
Among the flags in scan_control:
1. sc->may_swap, which indicates swap constraint due to memsw.max, is
supported as usual.
2. sc->proactive, which indicates reclaim by memory.reclaim, may not
opportunistically skip the aging path, since it is considered less
latency sensitive.
3. !(sc->gfp_mask & __GFP_IO), which indicates IO constraint, lowers
swappiness to prioritize file LRU, since clean file folios are more
likely to exist.
4. sc->may_writepage and sc->may_unmap, which indicates opportunistic
reclaim, are rejected, since unmapped clean folios are already
prioritized. Scanning for more of them is likely futile and can
cause high reclaim latency when there is a large number of memcgs.
The rest are handled by the existing code.
Link: https://lkml.kernel.org/r/20221222041905.2431096-8-yuzhao@xxxxxxxxxx
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Michael Larabel <Michael@xxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/vmscan.c~mm-multi-gen-lru-clarify-scan_control-flags
+++ a/mm/vmscan.c
@@ -3210,6 +3210,9 @@ static int get_swappiness(struct lruvec
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+ if (!sc->may_swap)
+ return 0;
+
if (!can_demote(pgdat->node_id, sc) &&
mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH)
return 0;
@@ -4236,7 +4239,7 @@ static void walk_mm(struct lruvec *lruve
} while (err == -EAGAIN);
}
-static struct lru_gen_mm_walk *set_mm_walk(struct pglist_data *pgdat)
+static struct lru_gen_mm_walk *set_mm_walk(struct pglist_data *pgdat, bool force_alloc)
{
struct lru_gen_mm_walk *walk = current->reclaim_state->mm_walk;
@@ -4244,7 +4247,7 @@ static struct lru_gen_mm_walk *set_mm_wa
VM_WARN_ON_ONCE(walk);
walk = &pgdat->mm_walk;
- } else if (!pgdat && !walk) {
+ } else if (!walk && force_alloc) {
VM_WARN_ON_ONCE(current_is_kswapd());
walk = kzalloc(sizeof(*walk), __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN);
@@ -4430,7 +4433,7 @@ static bool try_to_inc_max_seq(struct lr
goto done;
}
- walk = set_mm_walk(NULL);
+ walk = set_mm_walk(NULL, true);
if (!walk) {
success = iterate_mm_list_nowalk(lruvec, max_seq);
goto done;
@@ -4499,8 +4502,6 @@ static bool lruvec_is_reclaimable(struct
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MIN_SEQ(lruvec);
- VM_WARN_ON_ONCE(sc->memcg_low_reclaim);
-
/* see the comment on lru_gen_folio */
gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
@@ -4756,12 +4757,8 @@ static bool isolate_folio(struct lruvec
{
bool success;
- /* unmapping inhibited */
- if (!sc->may_unmap && folio_mapped(folio))
- return false;
-
/* swapping inhibited */
- if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) &&
+ if (!(sc->gfp_mask & __GFP_IO) &&
(folio_test_dirty(folio) ||
(folio_test_anon(folio) && !folio_test_swapcache(folio))))
return false;
@@ -4858,9 +4855,8 @@ static int scan_folios(struct lruvec *lr
__count_vm_events(PGSCAN_ANON + type, isolated);
/*
- * There might not be eligible pages due to reclaim_idx, may_unmap and
- * may_writepage. Check the remaining to prevent livelock if it's not
- * making progress.
+ * There might not be eligible folios due to reclaim_idx. Check the
+ * remaining to prevent livelock if it's not making progress.
*/
return isolated || !remaining ? scanned : 0;
}
@@ -5120,9 +5116,7 @@ static long get_nr_to_scan(struct lruvec
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MAX_SEQ(lruvec);
- if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg) ||
- (mem_cgroup_below_low(sc->target_mem_cgroup, memcg) &&
- !sc->memcg_low_reclaim))
+ if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
return 0;
if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan))
@@ -5150,17 +5144,14 @@ static bool try_to_shrink_lruvec(struct
long nr_to_scan;
unsigned long scanned = 0;
unsigned long nr_to_reclaim = get_nr_to_reclaim(sc);
+ int swappiness = get_swappiness(lruvec, sc);
+
+ /* clean file folios are more likely to exist */
+ if (swappiness && !(sc->gfp_mask & __GFP_IO))
+ swappiness = 1;
while (true) {
int delta;
- int swappiness;
-
- if (sc->may_swap)
- swappiness = get_swappiness(lruvec, sc);
- else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc))
- swappiness = 1;
- else
- swappiness = 0;
nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness);
if (nr_to_scan <= 0)
@@ -5291,12 +5282,13 @@ static void lru_gen_shrink_lruvec(struct
struct blk_plug plug;
VM_WARN_ON_ONCE(global_reclaim(sc));
+ VM_WARN_ON_ONCE(!sc->may_writepage || !sc->may_unmap);
lru_add_drain();
blk_start_plug(&plug);
- set_mm_walk(lruvec_pgdat(lruvec));
+ set_mm_walk(NULL, sc->proactive);
if (try_to_shrink_lruvec(lruvec, sc))
lru_gen_rotate_memcg(lruvec, MEMCG_LRU_YOUNG);
@@ -5352,11 +5344,19 @@ static void lru_gen_shrink_node(struct p
VM_WARN_ON_ONCE(!global_reclaim(sc));
+ /*
+ * Unmapped clean folios are already prioritized. Scanning for more of
+ * them is likely futile and can cause high reclaim latency when there
+ * is a large number of memcgs.
+ */
+ if (!sc->may_writepage || !sc->may_unmap)
+ goto done;
+
lru_add_drain();
blk_start_plug(&plug);
- set_mm_walk(pgdat);
+ set_mm_walk(pgdat, sc->proactive);
set_initial_priority(pgdat, sc);
@@ -5374,7 +5374,7 @@ static void lru_gen_shrink_node(struct p
clear_mm_walk();
blk_finish_plug(&plug);
-
+done:
/* kswapd should never fail */
pgdat->kswapd_failures = 0;
}
@@ -5943,7 +5943,7 @@ static ssize_t lru_gen_seq_write(struct
set_task_reclaim_state(current, &sc.reclaim_state);
flags = memalloc_noreclaim_save();
blk_start_plug(&plug);
- if (!set_mm_walk(NULL)) {
+ if (!set_mm_walk(NULL, true)) {
err = -ENOMEM;
goto done;
}
_
Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are
mm-multi-gen-lru-rename-lru_gen_struct-to-lru_gen_folio.patch
mm-multi-gen-lru-rename-lrugen-lists-to-lrugen-folios.patch
mm-multi-gen-lru-remove-eviction-fairness-safeguard.patch
mm-multi-gen-lru-remove-aging-fairness-safeguard.patch
mm-multi-gen-lru-shuffle-should_run_aging.patch
mm-multi-gen-lru-per-node-lru_gen_folio-lists.patch
mm-multi-gen-lru-clarify-scan_control-flags.patch
mm-multi-gen-lru-simplify-arch_has_hw_pte_young-check.patch
