mm/damon/schemes: add 'LRU_DEPRIO' action

This commit adds a new DAMON-based operation scheme action called
'LRU_DEPRIO' for physical address space.  The action deprioritizes pages
in the memory area of the target access pattern on their LRU lists.  This
is hence supposed to be used for rarely accessed (cold) memory regions so
that cold pages could be more likely reclaimed first under memory
pressure.  Internally, it simply calls 'lru_deactivate()'.

Using this with 'LRU_PRIO' action for hot pages, users can proactively
sort LRU lists based on the access pattern.  That is, it can make the LRU
lists somewhat more trustworthy source of access temperature.  As a
result, efficiency of LRU-lists based mechanisms including the reclamation
target selection could be improved.

Link: https://lkml.kernel.org/r/20220613192301.8817-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/damon.h

@@ -87,6 +87,7 @@ struct damon_target {
  * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
  * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
  * @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.
  * @NR_DAMOS_ACTIONS:	Total number of DAMOS actions
  */
@@ -97,6 +98,7 @@ enum damos_action {
 	DAMOS_HUGEPAGE,
 	DAMOS_NOHUGEPAGE,
 	DAMOS_LRU_PRIO,
+	DAMOS_LRU_DEPRIO,
 	DAMOS_STAT,		/* Do nothing but only record the stat */
 	NR_DAMOS_ACTIONS,
 };

mm/damon/paddr.c

@@ -249,6 +249,22 @@ static unsigned long damon_pa_mark_accessed(struct damon_region *r)
 	return applied * PAGE_SIZE;
 }
 
+static unsigned long damon_pa_deactivate_pages(struct damon_region *r)
+{
+	unsigned long addr, applied = 0;
+
+	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
+		struct page *page = damon_get_page(PHYS_PFN(addr));
+
+		if (!page)
+			continue;
+		deactivate_page(page);
+		put_page(page);
+		applied++;
+	}
+	return applied * PAGE_SIZE;
+}
+
 static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 		struct damon_target *t, struct damon_region *r,
 		struct damos *scheme)
@@ -258,6 +274,8 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 		return damon_pa_pageout(r);
 	case DAMOS_LRU_PRIO:
 		return damon_pa_mark_accessed(r);
+	case DAMOS_LRU_DEPRIO:
+		return damon_pa_deactivate_pages(r);
 	default:
 		break;
 	}
@@ -273,6 +291,8 @@ static int damon_pa_scheme_score(struct damon_ctx *context,
 		return damon_pageout_score(context, r, scheme);
 	case DAMOS_LRU_PRIO:
 		return damon_hot_score(context, r, scheme);
+	case DAMOS_LRU_DEPRIO:
+		return damon_pageout_score(context, r, scheme);
 	default:
 		break;
 	}

mm/damon/sysfs.c

@@ -763,6 +763,7 @@ static const char * const damon_sysfs_damos_action_strs[] = {
 	"hugepage",
 	"nohugepage",
 	"lru_prio",
+	"lru_deprio",
 	"stat",
 };