[RFC PATCH 2/4] mm/damon: introduce DAMOS_DEMOTE action for demotion

Honggyu Kim
2024-01-15T04:53:07Z

This patch introduces DAMOS_DEMOTE action, which is similar to
DAMOS_PAGEOUT, but demote folios instead of swapping them out.

Since there are some common routines with pageout, many functions have
similar logics between pageout and demote.

The execution sequence of DAMOS_PAGEOUT and DAMOS_DEMOTE look as follows.

DAMOS_PAGEOUT action
damo_pa_apply_scheme
-> damon_pa_reclaim
-> reclaim_pages
-> reclaim_folio_list
-> shrink_folio_list

DAMOS_DEMOTE action
damo_pa_apply_scheme
-> damon_pa_reclaim
-> demote_pages
-> do_demote_folio_list
-> __demote_folio_list
-> demote_folio_list

__demote_folio_list() is a minimized version of shrink_folio_list(), but
it's minified only for demotion.

Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
---
include/linux/damon.h | 2 +
mm/damon/paddr.c | 17 +++++---
mm/damon/sysfs-schemes.c | 1 +
mm/internal.h | 1 +
mm/vmscan.c | 84 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 99 insertions(+), 6 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index e00ddf1ed39c..4c0a0fef09c5 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -106,6 +106,7 @@ struct damon_target {
* @DAMOS_LRU_PRIO: Prioritize the region on its LRU lists.
* @DAMOS_LRU_DEPRIO: Deprioritize the region on its LRU lists.
* @DAMOS_STAT: Do nothing but count the stat.
+ * @DAMOS_DEMOTE: Do demotion for the current region.
* @NR_DAMOS_ACTIONS: Total number of DAMOS actions
*
* The support of each action is up to running &struct damon_operations.
@@ -123,6 +124,7 @@ enum damos_action {
DAMOS_LRU_PRIO,
DAMOS_LRU_DEPRIO,
DAMOS_STAT, /* Do nothing but only record the stat */
+ DAMOS_DEMOTE,
NR_DAMOS_ACTIONS,
};

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 081e2a325778..d3e3f077cd00 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -224,7 +224,7 @@ static bool damos_pa_filter_out(struct damos *scheme, struct folio *folio)
return false;
}

-static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
+static unsigned long damon_pa_reclaim(struct damon_region *r, struct damos *s, bool is_demote)
{
unsigned long addr, applied;
LIST_HEAD(folio_list);
@@ -242,14 +242,17 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
folio_test_clear_young(folio);
if (!folio_isolate_lru(folio))
goto put_folio;
- if (folio_test_unevictable(folio))
+ if (folio_test_unevictable(folio) && !is_demote)
folio_putback_lru(folio);
else
list_add(&folio->lru, &folio_list);
put_folio:
folio_put(folio);
}
- applied = reclaim_pages(&folio_list);
+ if (is_demote)
+ applied = demote_pages(&folio_list);
+ else
+ applied = reclaim_pages(&folio_list);
cond_resched();
return applied * PAGE_SIZE;
}
@@ -297,13 +300,15 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
{
switch (scheme->action) {
case DAMOS_PAGEOUT:
- return damon_pa_pageout(r, scheme);
+ return damon_pa_reclaim(r, scheme, false);
case DAMOS_LRU_PRIO:
return damon_pa_mark_accessed(r, scheme);
case DAMOS_LRU_DEPRIO:
return damon_pa_deactivate_pages(r, scheme);
case DAMOS_STAT:
break;
+ case DAMOS_DEMOTE:
+ return damon_pa_reclaim(r, scheme, true);
default:
/* DAMOS actions that not yet supported by 'paddr'. */
break;
@@ -317,11 +322,11 @@ static int damon_pa_scheme_score(struct damon_ctx *context,
{
switch (scheme->action) {
case DAMOS_PAGEOUT:
+ case DAMOS_LRU_DEPRIO:
+ case DAMOS_DEMOTE:
return damon_cold_score(context, r, scheme);
case DAMOS_LRU_PRIO:
return damon_hot_score(context, r, scheme);
- case DAMOS_LRU_DEPRIO:
- return damon_cold_score(context, r, scheme);
default:
break;
}
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index fe0fe2562000..ac7cd3f17b12 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1187,6 +1187,7 @@ static const char * const damon_sysfs_damos_action_strs[] = {
"lru_prio",
"lru_deprio",
"stat",
+ "demote",
};

static struct damon_sysfs_scheme *damon_sysfs_scheme_alloc(
diff --git a/mm/internal.h b/mm/internal.h
index b61034bd50f5..2380397ec2f3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -869,6 +869,7 @@ extern void set_pageblock_order(void);
unsigned long reclaim_pages(struct list_head *folio_list);
unsigned int reclaim_clean_pages_from_list(struct zone *zone,
struct list_head *folio_list);
+unsigned long demote_pages(struct list_head *folio_list);
/* The ALLOC_WMARK bits are used as an index to zone->watermark */
#define ALLOC_WMARK_MIN WMARK_MIN
#define ALLOC_WMARK_LOW WMARK_LOW
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7ca2396ccc3b..eaa3dd6b7562 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -998,6 +998,66 @@ static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)
return !data_race(folio_swap_flags(folio) & SWP_FS_OPS);
}

+/*
+ * __demote_folio_list() returns the number of demoted pages
+ */
+static unsigned int __demote_folio_list(struct list_head *folio_list,
+ struct pglist_data *pgdat, struct scan_control *sc)
+{
+ LIST_HEAD(ret_folios);
+ LIST_HEAD(demote_folios);
+ unsigned int nr_demoted = 0;
+
+ if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
+ return 0;
+
+ cond_resched();
+
+ while (!list_empty(folio_list)) {
+ struct folio *folio;
+ enum folio_references references;
+
+ cond_resched();
+
+ folio = lru_to_folio(folio_list);
+ list_del(&folio->lru);
+
+ if (!folio_trylock(folio))
+ goto keep;
+
+ VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
+
+ references = folio_check_references(folio, sc);
+ if (references == FOLIOREF_KEEP)
+ goto keep_locked;
+
+ /* Relocate its contents to another node. */
+ list_add(&folio->lru, &demote_folios);
+ folio_unlock(folio);
+ continue;
+keep_locked:
+ folio_unlock(folio);
+keep:
+ list_add(&folio->lru, &ret_folios);
+ VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
+ }
+ /* 'folio_list' is always empty here */
+
+ /* Migrate folios selected for demotion */
+ nr_demoted += demote_folio_list(&demote_folios, pgdat);
+ /* Folios that could not be demoted are still in @demote_folios */
+ if (!list_empty(&demote_folios)) {
+ /* Folios which weren't demoted go back on @folio_list */
+ list_splice_init(&demote_folios, folio_list);
+ }
+
+ try_to_unmap_flush();
+
+ list_splice(&ret_folios, folio_list);
+
+ return nr_demoted;
+}
+
/*
* shrink_folio_list() returns the number of reclaimed pages
*/
@@ -2107,6 +2167,25 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
return nr_reclaimed;
}

+static unsigned int do_demote_folio_list(struct list_head *folio_list,
+ struct pglist_data *pgdat)
+{
+ unsigned int nr_demoted;
+ struct folio *folio;
+ struct scan_control sc = {
+ .gfp_mask = GFP_KERNEL,
+ };
+
+ nr_demoted = __demote_folio_list(folio_list, pgdat, &sc);
+ while (!list_empty(folio_list)) {
+ folio = lru_to_folio(folio_list);
+ list_del(&folio->lru);
+ folio_putback_lru(folio);
+ }
+
+ return nr_demoted;
+}
+
static unsigned long reclaim_or_migrate_folios(struct list_head *folio_list,
unsigned int (*handler)(struct list_head *, struct pglist_data *))
{
@@ -2146,6 +2225,11 @@ unsigned long reclaim_pages(struct list_head *folio_list)
return reclaim_or_migrate_folios(folio_list, reclaim_folio_list);
}

+unsigned long demote_pages(struct list_head *folio_list)
+{
+ return reclaim_or_migrate_folios(folio_list, do_demote_folio_list);
+}
+
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
struct lruvec *lruvec, struct scan_control *sc)
{
--
2.34.1